Memory device and method for sensing and fixing margin cells

Abstract
A programmable resistance memory device with a margin cell detection and refresh resources. Margin cell detection and refresh can include reading a selected cell, measuring a time interval which correlates with resistance of the selected cell during said reading, and enabling a refresh process if the measured time falls within a pre-specified range. The refresh process includes determining a data value stored in the selected cell, using for example a destructive read process, and refreshing the data value in the selected cell. The time interval can be measured by detecting timing within the sensing interval of a transition of voltage or current on a bit line across a threshold.
Description
PARTIES TO A JOINT RESEARCH AGREEMENT

International Business Machines Corporation, a New York corporation, and Macronix International Corporation, Ltd., a Taiwan corporation, are parties to a Joint Research Agreement.


BACKGROUND OF THE INVENTION

1. Field of the Invention


The present invention relates to programmable resistance memory devices, including phase change memory devices, and to refresh techniques associated with maintaining data values stored in such devices.


2. Description of Related Art


Phase change based memory materials, like chalcogenide based materials and similar materials, can be caused to change phase in active regions of a memory element between an amorphous phase and a crystalline phase by application of electrical current at levels suitable for implementation in integrated circuits. The amorphous phase is characterized by higher electrical resistivity than the crystalline phase, and the difference in resistance can be readily sensed to indicate data.


In order to achieve high density memory, smaller memory cell structures are needed. However, attempts to reduce the size of the phase change material element and/or the electrodes can result in data retention issues. For example, in a memory cell programmed to a high resistance state having amorphous phase material in an active region of the memory element, environmental conditions can result in drift in the resistance due to re-crystallization of small portions of the active region. When the resistance drifts out of the sensing margin specified for the programmed data value, then the data is lost. Similar issues can arise in other types of programmable resistance memory materials.


Thus, methods to improve data retention for phase change memory devices based on refresh operations like those encountered in dynamic random access memory have been investigated. See, United States Patent Application Publication No. US 2006/0158948 A1, by Fuji.


However, the need remains for efficient technologies to detect cells that need refresh (called margin cells herein), and to refresh such cells with correct data values.


SUMMARY

A method for operating a memory device with a margin cell detection and refresh process, where the memory device includes an array of programmable resistance memory cells such as cells having phase change memory elements, and a set of sense amplifiers coupled to the array which sense changes of voltage or current on bit lines coupled to selected memory cells. The method for margin cell detection and refresh comprises reading a selected cell, measuring a time interval which correlates with resistance of the selected cell during said reading, and enabling a refresh process if the measured time falls within a pre-specified range. The refresh process includes determining a data value stored in the selected cell, and refreshing the data value in the selected cell. The time interval can be measured by detecting timing within a sensing interval with which the sense amplifier operates, of a transition of voltage or current on a bit line across a threshold.


The data value stored in the selected cell can be determined by storing a first parameter indicating length of the measured time interval for the selected cell, writing a reference data value to the selected cell, measuring a second time interval which correlates with resistance of the selected cell after writing the reference data value, storing a second parameter indicating length of the second time interval, and comparing the first parameter to the second parameter.


In embodiments in which the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, the reference data value can be either the first data value or the second data value. In the case in which the first data value (set state) is used, then the process indicates the data value of the selected cell is the second data value (reset state) if the first parameter is greater than the second parameter by more than a predetermined amount, else the data value of the selected cell is the first data value. If the data value of the selected cell is indicated to be the second data value, then a process is executed to write the second data value to the selected cell. In the case in which the second data value (reset state) is used as said reference data value, then the process indicates the data value of the selected cell is the first data value (set state) if the first parameter is less than the second parameter by more than a predetermined amount. If the data value of the selected cell is indicated to be the first data value, then a process is executed to write the first data value to the selected cell.


In some embodiments, where the memory device includes logic which executes write processes for writing data values in the array, the write processes including a set process to store a first data value(set state) in a selected cell and a reset process to store a second data value (reset state)in a selected cell. The set and reset processes for normal write operations are characterized by a set biasing arrangement and a reset biasing arrangement. The refresh set process to refresh the first data value in a selected cell can include applying a refresh set biasing arrangement that is different than the set biasing arrangement applied in normal write mode. Likewise, the refresh reset process to refresh the second data value in a selected cell can include applying a refresh reset biasing arrangement that is different than the reset biasing arrangement applied in normal write mode. Different biasing arrangements for refresh reset and set can be applied that have higher power, or longer pulses, in order to enable resetting or setting cells that are hard to program using normal write mode biasing arrangements.


In one embodiment described herein, a controller determines the data value stored in the selected cell by executing a process including storing an initial resistance of the margin cell, setting the selected cell to the set state, measuring a set state resistance, resetting the selected cell to the reset state, measuring a reset state resistance, and indicating that the data value of the selected cell is the first data value if the initial resistance is closer to the set state resistance than to the reset state resistance, else that the data value of the selected cell is the second data value. The set and reset steps can be executed in any order.


In addition, a memory device is disclosed including circuitry adapted to carry out the processes described above. The memory device includes an array of programmable resistance memory cells, a set of sense amplifiers coupled to the array which sense within sensing intervals changes of voltage or current on bit lines coupled to selected memory cells, timer circuitry coupled to the array which measures time intervals which correlate with resistance of a corresponding selected cell, logic responsive to the measured time for a selected cell to enable refresh logic if the measured time falls within a pre-specified range. As described above, the refresh logic includes logic to determine a data value stored in the selected cell, and to refresh the data value in the selected cell.


Other aspects and advantages of the present invention can be seen on review of the drawings, the detailed description and the claims, which follow.





BRIEF DESCRIPTION OF THE DRAWINGS


FIG. 1 is a simplified block diagram of an integrated circuit, programmable resistance memory device having logic to execute a margin cell detection and refresh process.



FIG. 2 is a simplified diagram of a prior art, programmable resistance memory cell, having a phase change memory element suitable for use in a device as shown in FIG. 1.



FIG. 3 is a graph showing probability distributions for resistance for high resistance and low resistance states for a programmable resistance memory cell for an ideal case, without margin cells.



FIG. 4 is a graph showing probability distributions for resistance for high resistance and low resistance states for a programmable resistance memory cell for a case in which margin cells exist.



FIG. 5 is a circuit diagram of a prior art sense amplifier circuit, suitable for use in devices as described herein.



FIG. 6 is a graph showing probability distributions for sensing time for high resistance and low resistance states for a programmable resistance memory cell.



FIG. 7 is a block diagram of a memory device including circuitry for margin cell detection and refresh.



FIG. 8 is a flow chart of a first alternative process for margin cell detection and refresh.



FIG. 9 is a flow chart of a second alternative process for margin cell detection and refresh.



FIG. 10 is a flow chart of a third alternative process for margin cell detection and refresh.



FIG. 11 is a flow chart of a fourth alternative process for margin cell detection and refresh.





DETAILED DESCRIPTION

A detailed description of embodiments of the present invention is provided with reference to the FIGS. 1-11.



FIG. 1 is a simplified block diagram of an integrated circuit 110 including a memory array 112 implemented using programmable resistance memory cells, such as memory cells having phase change memory elements. A word line decoder 114 is coupled to and in electrical communication with a plurality of word lines 116 arranged along rows in the memory array 112. A bit line (column) decoder 118 is in electrical communication with a plurality of bit lines 120 arranged along columns in the array 112 for coupling selected memory cells in array 112 to sense amplifiers in sense circuitry 124. Addresses are supplied on bus 122 to word line decoder 114 and bit line decoder 118. Sense circuitry 124, including sense amplifiers and data-in structures, is coupled to bit line decoder 118 via data bus 126. Data is supplied via a data-in line 128 from input/output ports on integrated circuit 110, or from other data sources internal or external to integrated circuit 110, to data-in structures in sense circuitry 124. Other circuitry 130 may be included on integrated circuit 110, such as a general-purpose processor or special purpose application circuitry, or a combination of modules providing system-on-a-chip functionality supported by array 112. Data is supplied via a data-out line 132 from the sense amplifiers in circuitry 124 to input/output ports on integrated circuit 110, or to other data destinations internal or external to integrated circuit 110. Margin cell detection circuitry 125 is coupled with the sense circuitry 124 in this example.


A controller 134 is implemented in this example using a state machine to execute processes described below, and controls the bias circuitry voltage and current sources 136 for the application of bias arrangements for a read mode with margin detection, a write mode and a refresh write mode. Controller 134 may be implemented using special-purpose logic circuitry as known in the art. In alternative embodiments, controller 134 comprises a general-purpose processor, which may be implemented on the same integrated circuit to execute a computer program to control the operations of the device. In yet other embodiments, a combination of special-purpose logic circuitry and a general-purpose processor may be utilized for implementation of controller 134.


The bias circuitry voltage and current sources in block 136 can be implemented using power supply inputs with voltage dividers and charge pumps, current source circuitry, pulse shaping circuitry, timing circuitry and voltage and current switches as are standard in the art.


In operation each of the memory cells in the array 112 stores data represented by the resistance of the corresponding memory element. The data value may be determined, for example, by comparison of voltage or current on a bit line for a selected memory cell to that of a suitable reference current or voltage by sense amplifiers in sense circuitry 124. The reference voltage or current can be established to between a predetermined range corresponding to a data value such as logical “0”, and a different predetermined range corresponding to a data value such as logical “1”.


Reading or writing to a memory cell of array 112, therefore, can be achieved by applying biasing arrangements including a suitable voltage to one of word lines and coupling one of bit lines to a voltage source so that current flows through the selected memory cell.


The write mode includes set and reset process for phase change memory. In biasing arrangements for a reset operation for a phase change memory cell, word line decoder 114 facilitates providing a word line with a suitable voltage pulse to turn on an access transistor of the memory cell. Bit line decoder 118 facilitates supplying a voltage pulse to a bit line of suitable amplitude and duration to induce a current to flow though the memory element, the current raising the temperature of the active region of the memory element above the transition temperature of the phase change material and also above the melting temperature to place the phase change material of the active region in a liquid state. The current is then terminated, for example, by terminating the voltage pulses on the bit line and on the word line, resulting in a relatively quick quenching time as the active region cools to a high resistance generally amorphous phase to establish a high resistance reset state in the memory cell. The reset operation can also comprise more than one pulse, for example using a pair of pulses.


In biasing arrangements for a set operation for a phase change memory cell, word line decoder 114 facilitates providing a word line with a suitable voltage pulse to turn on the access transistor of the memory cell. Bit line decoder 118 facilitates supplying a voltage pulse to a bit line of suitable amplitude and duration to induce a current to flow through the memory element, the current pulse sufficient to raise the temperature of the active region above the transition temperature and cause a transition in the active region from the high resistance generally amorphous phase into a low resistance generally crystalline phase, this transition lowering the resistance of all of the memory element and setting the memory cell to the low resistance state.


In a read mode for the memory cell, word line decoder 114 facilitates providing a word line with a suitable voltage pulse to turn on the access transistor of the memory cell. Bit line decoder 118 facilitates supplying a voltage to a bit line of suitable amplitude and duration to induce current to flow through the memory element that does not result in the memory element undergoing a change in resistive state. The current on the bit line and through the memory cell is dependent upon the resistance of, and therefore the data state associated with, the memory cell. Thus, the data state of the memory cell may be determined by detecting whether the resistance of the memory cell corresponds to the high resistance state or the low resistance state, for example by comparison of a voltage or a current on the corresponding bit line with a suitable reference voltage or current by sense amplifiers of sense circuitry 124. The margin cell detection circuitry 125 operates in coordination with the read mode in the examples described herein.


In a refresh mode, the control circuitry in controller 134 executes a procedure described in more detail below.



FIG. 2 illustrates a representative prior art programmable resistance memory cell having phase change memory element. The example structure shown in FIG. 2 is referred to as a “mushroom type” memory cell 10, having a first electrode 11 extending through dielectric 12, a memory element 13 comprising a body of phase change material, and a second electrode 14 on the memory element 13. The first electrode 11 is coupled to a terminal of an access device (not shown) such as a diode or transistor, while the second electrode 14 is coupled to a bit line and can be part of the bit line (not shown). The first electrode 11 has a width less than the width of the second electrode 14 and memory element 13, establishing a small contact area between the body of phase change material and the first electrode 11 and a relatively larger contact area between the body of phase change material and the second electrode 14, so that higher current densities are achieved with small absolute current values through the memory element 13. Because of this smaller contact area at the first electrode 11, the current density is largest in operation in the region adjacent the first electrode 11, resulting in the active region 15 having a “mushroom” shape as shown in the Figure. Other types of phase change memory elements, such as pore type elements, bridge type elements, in-via type elements and so on, can be utilized in devices described herein.


Memory cells having phase change memory elements can suffer drift in resistance, as the active region composition shifts from amorphous phase to crystalline phase, or vice versa, in small increments or in filaments through the active region, depending on environmental factors. The rate of the drift in resistance depends on a number of factors, including variations in structure across an array, manufacturing defects in the cells and environmental conditions to which the device is exposed.


The phase change material used in a representative embodiment can consist of silicon oxide doped G2S2T5. Other phase change alloys including chalcogenides may be used as well. Chalcogens include any of the four elements oxygen (0), sulfur (S), selenium (Se), and tellurium (Te), forming part of group VIA of the periodic table. Chalcogenides comprise compounds of a chalcogen with a more electropositive element or radical. Chalcogenide alloys comprise combinations of chalcogenides with other materials such as transition metals. A chalcogenide alloy usually contains one or more elements from group IVA of the periodic table of elements, such as germanium (Ge) and tin (Sn). Often, chalcogenide alloys include combinations including one or more of antimony (Sb), gallium (Ga), indium (In), and silver (Ag). Many phase change based memory materials have been described in technical literature, including alloys of: Ga/Sb, In/Sb, In/Se, Sb/Te, Ge/Te, Ge/Sb/Te, In/Sb/Te, Ga/Se/Te, Sn/Sb/Te, In/Sb/Ge, Ag/In/Sb/Te, Ge/Sn/Sb/Te, Ge/Sb/Se/Te and Te/Ge/Sb/S. In the family of Ge/Sb/Te alloys, a wide range of alloy compositions may be workable. The compositions can be characterized as TeaGebSb100-(a-b). One researcher has described the most useful alloys as having an average concentration of Te in the deposited materials well below 70%, typically below about 60% and ranged in general from as low as about 23% up to about 58% Te and most preferably about 48% to 58% Te. Concentrations of Ge were above about 5% and ranged from a low of about 8% to about 30% average in the material, remaining generally below 50%. Most preferably, concentrations of Ge ranged from about 8% to about 40%. The remainder of the principal constituent elements in this composition was Sb. These percentages are atomic percentages that total 100% of the atoms of the constituent elements. (Ovshinsky U.S. Pat. No. 5,687,112 patent, cols. 10-11.) Particular alloys evaluated by another researcher include Ge2Sb2Te5, GeSb2Te4 and GeSb4Te7 (Noboru Yamada, “Potential of Ge—Sb—Te Phase-Change Optical Disks for High-Data-Rate Recording”, SPIE v.3109, pp. 28-37 (1997).) More generally, a transition metal such as chromium (Cr), iron (Fe), nickel (Ni), niobium (Nb), palladium (Pd), platinum (Pt) and mixtures or alloys thereof may be combined with Ge/Sb/Te to form a phase change alloy that has programmable resistive properties. Specific examples of memory materials that may be useful are given in Ovshinsky '112 at columns 11-13, which examples are hereby incorporated by reference. Chalcogenides and other phase change materials are doped with impurities in some embodiments to modify conductivity, transition temperature, melting temperature, and other properties of memory elements using the doped chalcogenides. Representative impurities used for doping chalcogenides include nitrogen, silicon, oxygen, silicon dioxide, silicon nitride, copper, silver, gold, aluminum, aluminum oxide, tantalum, tantalum oxide, tantalum nitride, titanium and titanium oxide. See, e.g. U.S. Pat. No. 6,800,504, and U.S. Patent Application Publication No. US 2005/0029502.


Representative chalcogenide material can have a bulk stoichiometry characterized as follows: GexSbyTez, where x:y:z=2:2:5. Other compositions can be used with x: 0˜5; y: 0˜5; z: 0˜10. GeSbTe with doping, such as N—, Si—, Ti—, or other element doping, may also be used. These materials can be formed by PVD sputtering or magnetron-sputtering with reactive gases of Ar, N2, and/or He, etc. and chalcogenide at the pressure of 1 mtorr˜100 mtorr. The deposition is usually done at room temperature. A collimator with an aspect ratio of 1˜5 can be used to improve the fill-in performance. To improve the fill-in performance, the DC bias of several tens of volts to several hundreds of volts is also used. Also, the combination of DC bias and the collimator can be used simultaneously. A post deposition annealing treatment with vacuum or N2 ambient is sometimes needed to improve the crystallized state of chalcogenide material. The annealing temperature typically ranges 100° C. to 400° C. with an anneal time of less than 30 minutes.


The thickness of the chalcogenide material depends on the design of the cell structure. In general, a chalcogenide material with thickness of higher than 8 nm can have a phase change characterization such that the material exhibits at least two stable resistance states, although thinner layers may be suitable for some embodiments.


For memory cells implemented using GST or similar chalcogenides, suitable materials for implementing electrodes include TiN , TaN, W and doped Si. Alternatively, the electrodes are TiAlN or TaAlN, or comprise, for further examples, one or more elements selected from the group consisting of Ti, W, Mo, Al, Ta, Cu, Pt, Ir, La, Ni, and Ru and alloys thereof.


The technology described herein can also be applied to other types of programmable resistance materials, such as devices having metal oxide memory elements using NixOy; TixOy; AlxOy; WxOy; ZnxOy; ZrxOy; CuxOy (x: 0˜1; y: 0˜1), CMR (colossal magneto resistance) material like PrxCayMnO3 (x: 0˜1; y: 0˜1), polymer materials like TCNQ with doping of Cu, C60, Ag etc., and PCBM-TCNQ mixed polymers.



FIG. 3 is a heuristic graph showing ideal probability distributions for low resistance state 100 and high resistance state 102 in a programmable resistance memory device, such as that shown in FIG. 2. As shown, the maximum resistance R1 for the distribution for the low resistance state 100 is less than the minimum resistance R2 for the distribution for the high resistance state 102 by a significant margin. A reference level 103 can be used to reliably distinguish between the two states.



FIG. 4 is a heuristic graph showing more realistic probability distributions for the low resistance state 100′ and high resistance state 102′ and a phase change memory cell. As the resistance values drift, a number of cells in the low resistance state 100′ will have a resistance greater than R1 and a number of cells in the high resistance state 100′ will have a resistance less than R2. When cells in the low resistance state 100′ have resistance above the reference level 103, then the data value of the cell is lost. Likewise, when cells in the high resistance state 102′ have a resistance below the reference level 103, then the data is lost. It is desirable to detect margin cells that have resistances approaching the reference value, before the data is lost.



FIG. 5 illustrates a basic configuration for a prior art sense amplifier. The embodiment shown in FIG. 5 includes load transistor 40 and clamp transistor 41. A bias voltage VBIAS is produced by a reference voltage circuit, and applied to the gate of the clamp transistor 41. The source of the clamp transistor 41 is coupled to a selected memory cell through decoding circuitry not shown. The bit line capacitance is represented by the capacitor CBL. A selected memory cell 38 is coupled to the bit line 39. The sensing node between the load transistor 40 and the clamp transistor 41 is coupled to a sense amplifier 42. A sense enable signal SEN is applied to the sense amplifier 42, to define a sensing interval for a read operation for a selected cell. The sensing interval follows a precharge process in this example. As the voltage VBL on the bit line reaches a level that is about a threshold voltage drop across the clamp transistor 41 below the bias voltage VBIAS, the clamp transistor 41 begins to turn off and reduce current flow. The dynamic balance is achieved with the voltage at the sensing node VCELL settles on a target value. At this point, the pre-charge step is completed, and the bit line is ready for sensing. Upon accessing a memory cell, the cell data influences the voltage at the node VCELL, causing it to move downward more rapidly if the selected cell has a low resistance state, than if the selected cell has a high resistance state. The reference voltage VREF applied to the sense amplifier 42 is established at a value low enough that current through the selected memory cell during the sensing interval pulls the value at the sensing node VCELL below reference voltage VREF before the end of the sensing interval for memory cells in a low resistance state.


The sensing interval with which the sense amplifier in FIG. 5 operates can be timed in a variety of ways. In representative systems, the signal SEN has a leading edge 43 that is timed relative to detection of a transition of an address input during a read process using address transition detection ADT circuits. The trailing edge 44 of the signal SEN is selected based on the characteristics of the memory array, and defines the length of the sensing interval. The sensing interval must be long enough that the data value in the selected cells can be reliably sensed. Thus, the sensing interval must be long enough for the voltage at the sensing node VCELL to fall below the reference voltage VREF for all memory cells having a resistance within the window for the low resistance state, plus some margin. There is a large variety of sense amplifier designs usable with the present invention, of which the sense amplifier in FIG. 5 is one basic example. There are current mode sense amplifiers, differential sense amplifiers, latching sense amplifiers and so on, all which can be adapted for use with the present invention. Also, a variety of bit line precharge and biasing circuits can be applied as known in the art.



FIG. 6 is a heuristic graph showing probability distributions for sensing time corresponding to the low resistance state 100″ and high resistance state 102″ for a phase change memory cell. As can be seen by comparison with FIG. 4, the time required for the voltage on the sensing node to reach the reference voltage VREF, and trigger a transition in the sense amplifier output correlates with the resistance of the selected memory cell. Using a sense amplifier such that shown in FIG. 5, the time that it takes for the voltage or current on the bit line to fall below the reference voltage and cause a transition in the output of the sense amplifier correlates with the resistance of the cell. Thus, for memory cells in the low resistance state 100″, there is a specified maximum time TA (corresponding with R1 of FIG. 3) within which a sense amplifier transition should occur. For memory cells in the high resistance state 102″, there is a specified minimum time TB (corresponding with R2 of FIG. 3) within which a sense amplifier transition should occur. As described herein, measuring a time that it takes for a sense amplifier transition to occur can be used to detect memory cells operating in the margin between R1 (time TA) and R2 (time TB).



FIG. 7 illustrates circuitry on the integrated circuit, corresponding with the margin cell detection circuitry 125 on the integrated circuit of FIG. 1, which can be used to detect the margin cells, and in addition to determine a data value for them and refresh the data value. In this embodiment, the memory array 50 is coupled by bit line 51 through a decoder 52 to a sense amplifier 53. The reference voltage 54 is also coupled to the sense amplifier 53. A sense enable signal SEN is coupled to the sense amplifier 53, and during a read operation, enables the sense amplifier 53 to provide output data DOUT to a latch 55. In this embodiment, a counter 56 or other timing circuitry is coupled to the sense enable signal SEN and to the output of the sense amplifier 53. A clock is applied to the counter that enables high-speed counting relative to the length of the sensing interval. For example, for a sensing interval that is 50 nanoseconds wide, a counter operating in a range of 100 megahertz to one gigahertz could be provided. The counter begins counting upon the leading edge of the enable signal SEN and stops upon detection of a transition on the output of the sense amplifier 53. The value stored in counter indicates a time interval for sensing the data value in the selected cell, and also indicates a resistance value for the cell. The value stored in the counter can then be decoded and supplied to controller 57, such as the controller 134 of FIG. 1, to indicate valid data VLD or margin cell data MRG. For example, if the counter value, which indicates a measured time interval for the selected cell, exceeds a pre-specified minimum, then the output of the counter indicates a margin cell. For example, valid data for a low resistance state can be specified as causing a transition within the first 30 nanoseconds of the 50 nanosecond long sensing interval. Margin cell data is indicated when the transition occurs within the last 20 nanoseconds of the 50 nanosecond sensing interval. Valid data for a high resistance state can be specified as the case in which no transition is detected in the sensing interval. Also, other types of circuits for measuring the time interval which correlates with resistance of the selected cell can be used, including analog timers such as timers based on integration circuits with sample and hold circuits for results storage. When analog timers are used, the controller 57 may include analog comparators.


The circuitry shown in FIG. 7 also includes register set 58. In the event that the controller 57 detects that a selected memory cell is a margin cell, then it executes a process to determine the data value stored in the selected memory cell, representatives of which are described below with reference to FIGS. 8-10. As part of the processes described below, the register set 58 stores a parameter RI which represents the initial resistance, such as by storing the output of the counter, detected during the read. Register set 58 is used to store a parameter RP which represents the measured resistance of the selected cell that was programmed during the processes described below, to a pre-specified state such as the high resistance state or the low resistance state. The parameters RI, RP are used by the controller 57 to determine a data value for the margin cell for the refresh operation. Other parameters may also be stored in the register set.



FIG. 8 illustrates a first example process bases on a destructive read of the margin cell, which can be executed by the controller 57 upon detection of a margin cell using circuitry of FIG. 7. The process executed by the controller 57 first determines whether a margin cell is detected (200). If no margin cell is detected, the process loops to wait for such detection. If a margin cell is detected, then the controller causes a process to determine an initial resistance RI of the selected cell (201), such as by running a second read process, and storing a parameter indicating the resistance, such as output of the counter in the register set 58 (202). Alternatively, the initial read process in which the margin cell is detected can be utilized to supply the parameter RI. Next, the controller 57 causes the process to reset the cell, applying a reset bias arrangement (203). The reset bias arrangement can be a bias arrangement used for resetting the cell in normal write operations. After resetting cell, the cell resistance is again read (204). This process can be executed using a normal reading process, or an alternative reading process in which the sensing interval is extended to allow reading of higher timing values to extend the margin closer to the high resistance state range. The parameter RP can be a time within the sensing interval, or can saturate at a maximum value indicating no transition detection in the sensing interval. The parameter RP indicating resistance of the reset cell is stored in the register set 58 (205). Next, the parameters RI and RP are compared (206). If RI is much less than RP, which can be detected by determining whether the difference between the parameters is greater than a pre-specified value, then the data value of the margin cell is determined to be the value corresponding to a set state, or low resistance state (207). In this case, the controller 57 causes a process to set the cell, establishing a refreshed data value in the cell (208). At that point, the refresh process is completed (209) for the set state cell. If at block 206, it is detected that RI is not much less than RP, then the data value of the margin cell is determined to be the value corresponding to a reset state or high resistance state (210). At that point, the refresh process is completed (209) for the reset state cell.



FIG. 9 illustrates a second example process which can be executed by the controller 57 upon detection of a margin cell using a circuitry of FIG. 7, keying on a set process rather than a reset process as used in step 203 of FIG. 8. The process executed by the controller 57 first determines whether a margin cell is detected (210). If no margin cell is detected, the process loops to wait for such detection. If a margin cell is detected, then the controller causes the process to read the resistance RI of the selected cell (211), such as by running a read process, and storing a parameter indicating the resistance, such as output of the counter in the register set 58 (212). Alternatively, the initial read process in which the margin cell is detected can be utilized to supply the parameter RI. Next, the controller 57 causes a process to set the cell, applying a set bias arrangement (213). The set bias arrangement can be a bias arrangement used for setting the cell in normal operation. After setting cell, the cell resistance is again read (214). This process can be executed using a normal reading process, or an alternative reading process in which the sensing interval is extended to allow reading of higher timing values. The parameter RP indicating resistance of the set cell is stored in the register set 58 (215). Next, the parameters RI and RP are compared (216). If RI is much greater than RP, which can be detected by determining whether the difference between the parameters is greater than a pre-specified value, then the data value of the margin cell is determined to be the value corresponding to a reset state, or high resistance state (217). In this case, the controller 57 causes the process to reset the cell, establishing a refreshed data value in the cell (218). At that point, the refresh process is completed (219) for the reset state cell. If at block 206, it is detected that RI is not much greater than RP, then the data value of the margin cell is determined to be the value corresponding to a set state or low resistance state (210). At that point, the refresh process is completed (219) for the set state cell.



FIG. 10 illustrates a third example process which can be executed by the controller 57 upon detection of a margin cell using the circuitry of FIG. 7, in which the refresh operations use biasing arrangements for both the refresh set process and the refresh reset process which are different than the biasing arrangements used for normal mode set and reset processes. Alternative embodiments may use different biasing arrangements for only one of the set and refresh set pair of operations, and the reset and refresh reset pair of operations. The process executed by the controller 57 first determines whether a margin cell is detected (220). If no margin cell is detected, the process loops to wait for such detection. If a margin cell is detected, then the controller causes the process to read the resistance RI of the selected cell (221), such as by running a read process, and storing a parameter indicating the resistance, such as output of the counter in the register set 58 (222). Alternatively, the initial read process in which the margin cell is detected can be utilized to supply the parameter RI. Next, the controller 57 causes a process to reset the cell, applying a reset bias arrangement (223). The reset bias arrangement can be a bias arrangement used for resetting the cell in normal write operations. After resetting cell, the cell resistance is again read (224). This process can be executed using a normal reading process, or an alternative reading process in which the sensing interval is extended as explained above. The parameter RP indicating resistance of the set cell is stored in the register set 58 (225). Next, the parameters RI and RP are compared (226). If RI is much less than RP, which can be detected by determining whether the difference between the parameters is greater than a pre-specified value, then the data value of the margin cell is determined to be the value corresponding to a set state, or low resistance state (227). In this case, the controller 57 causes the process to cause a refresh set for the cell, establishing a refreshed data value in the cell (228). The refresh set process uses a bias arrangement different from that used in normal mode set process, such as by using a longer set pulse or higher power set pulse. At that point, the refresh process is completed (229) for the set state cell. If, at block 206, it is detected that RI is not much less than RP, then the data value of the margin cell is determined to be the value corresponding to a reset state or high resistance state (230). In this case, the controller 57 causes the process to cause a refresh reset for the cell, establishing a refreshed data value in the cell (231). The refresh reset process uses a bias arrangement different from that used in normal mode reset, such as by using a higher power reset pulse, or a reset pulse with a faster quench. At that point, the refresh process is completed (229) for the reset state cell.


The process of FIG. 10 can be adapted in an alternative to using the set state as the reference state, as is done in step 213 of FIG. 9.



FIG. 11 illustrates another example process bases on a destructive read of the margin cell, which can be executed by the controller 57 upon detection of a margin cell using circuitry of FIG. 7. In the process of FIG. 11, the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value. Logic executed by the controller to determine the data value stored in the selected cell executes a process including storing an initial resistance of the margin cell, setting the margin cell, measuring a set state resistance of the margin cell, resetting the margin cell, measuring a reset resistance of the margin cell, and indicating that the data value of the margin cell is the first data value if the first resistance is closer to the set state resistance than to the reset state resistance, else that the data value of the selected cell is the second data value. The set and reset steps can be executed in any order. In the illustrated example, the process executed by the controller 57 first determines whether a margin cell is detected (300). If no margin cell is detected, the process loops to wait for such detection. If a margin cell is detected, then the controller causes a process to determine an initial resistance RI of the selected cell (301), such as by running a second read process, and storing a parameter indicating the resistance, such as output of the counter in the register set 58 (302). Alternatively, the initial read process in which the margin cell is detected can be utilized to supply the parameter RI. Next, the controller 57 causes the process to reset the cell, applying a reset bias arrangement (303). The reset bias arrangement can be a bias arrangement used for resetting the cell in normal write operations. After resetting cell, the cell resistance R is again read (304). This process can be executed using a normal reading process, or an alternative reading process in which the sensing interval is extended to allow reading of higher timing values to extend the margin closer to the high resistance state range. The resistance R can be represented by a time within the sensing interval, or can saturate at a maximum value indicating no transition detection in the sensing interval. The difference between the reset cell resistance R and the initial resistance RI is stored as a parameter RPR (305). Next, the controller 57 causes a process to set the cell, applying a set bias arrangement (306). The set bias arrangement can be a bias arrangement used for setting the cell in normal operation. After setting cell, the cell resistance R is again read (307). This process can be executed using a normal reading process, or an alternative reading process in which the sensing interval is extended to allow reading of higher timing values. The difference between the initial resistance RI and the set cell resistance R is stored as a parameter RPS (308).


Next, the controller determines whether RPS is less than RPR (309). If it is determined that RPS is not less than RPR, (i.e. the initial resistance was closer to a reset resistance than to a set resistance), then the data value of the margin cell is determined to be the value corresponding to a reset state or high resistance state (310). At that point, the refresh process is completed (311) for the reset state cell. If at block 309, it is determined that RPS is less than RPR, (i.e. the initial resistance was closer to a set resistance than to a reset resistance) then the data value of the margin cell is determined to be the value corresponding to a set state, or low resistance state (312). In this case, the controller 57 causes a process to set the cell, establishing a refreshed data value in the cell (313). At that point, the refresh process is completed (311) for the set state cell.


In the case that RPS is equal to RPR, the system can issue an error signal, enabling the system to take corrective action, or can make a determination that the margin cell should be in one of the set and reset states, as suits the needs of the system. Also, as with the process of FIG. 10, after determining the expected state of the margin cell, then refresh set and refresh reset bias arrangements can be used to improve the likelihood that the margin cell will be successfully programmed, as explained above.


While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.

Claims
  • 1. A memory device, comprising: an array of programmable resistance memory cells;a sense amplifier coupled to the array, which senses changes of voltage or current on bit lines coupled to a selected memory cell;timer circuitry coupled to the array, which measures a time interval which correlates with resistance of the selected cell; andlogic responsive to the time interval for the selected cell, to enable refresh logic if the time interval has a duration that falls within a pre-specified range;said refresh logic including logic to determine a data value stored in the selected cell, and to refresh the data value in the selected cell, wherein said logic to determine a data value stored in the selected cell executes a process including storing a first parameter indicating length of the time interval for the selected cell, writing a reference data value to the selected cell, measuring a second time interval which correlates with resistance of the selected cell after said writing, storing a second parameter indicating length of the second time interval, and comparing the first parameter to the second parameter.
  • 2. The device of claim 1, wherein the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, and wherein said reference data value is the first data value, and including the step of indicating the data value of the selected cell is the second data value if the first parameter is greater than the second parameter by more than a predetermined amount, else the data value of the selected cell is the first data value.
  • 3. The device of claim 2, including if the data value of the selected cell is indicated to be the second data value, then writing the second data value to the selected cell.
  • 4. The device of claim 1, wherein the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, and wherein said reference data value is the second data value, and including the step of indicating the data value of the selected cell is the first data value if the first parameter is less than the second parameter by more than a predetermined amount.
  • 5. The device of claim 4, including if the data value of the selected cell is indicated to be the first data value, then writing the first data value to the selected cell.
  • 6. A memory device, comprising: an array of programmable resistance memory cells;a sense amplifier coupled to the array, which senses changes of voltage or current on bit lines coupled to a selected memory cell;timer circuitry coupled to the array, which measures a time interval which correlates with resistance of the selected cell; andlogic responsive to the time interval for the selected cell, to enable refresh logic if the time interval has a duration that falls within a pre-specified range;said refresh logic including logic to determine a data value stored in the selected cell, and to refresh the data value in the selected cell, wherein the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, and wherein said logic to determine the data value stored in the selected cell executes a process including storing a first resistance of the selected cell, setting the selected cell to the set state, measuring a set state resistance, resetting the selected cell to the reset state, measuring a reset state resistance, and indicating that the data value of the selected cell is the first data value if the first resistance is closer to the set state resistance than to the reset state resistance, else that the data value of the selected cell is the second data value.
  • 7. A method for operating a memory device including an array of programmable resistance memory cells, and a sense amplifier coupled to the array which senses changes of voltage or current on a bit line coupled to a selected memory cell; the method comprising: reading the selected cell;measuring a time interval which correlates with resistance of the selected cell during said reading; andenabling a refresh process if the time interval has a duration that falls within a pre-specified range;said refresh process including determining a data value stored in the selected cell, and refreshing the data value in the selected cell, wherein said determining a data value stored in the selected cell includes storing a first parameter indicating length of the time interval for the selected cell, writing a reference data value to the selected cell, measuring a second time interval which correlates with resistance of the selected cell after said writing, storing a second parameter indicating length of the second time interval, and comparing the first parameter to the second parameter.
  • 8. The method of claim 7, wherein the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, and wherein said reference data value is the first data value, and including the step of indicating the data value of the selected cell is the second data value if the first parameter is greater than the second parameter by more than a predetermined amount, else the data value of the selected cell is the first data value.
  • 9. The method of claim 8, including if the data value of the selected cell is indicated to be the second data value, then writing the second data value to the selected cell.
  • 10. The method of claim 7, wherein the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, and wherein said reference data value is the second data value, and including the step of indicating the data value of the selected cell is the first data value if the first parameter is less than the second parameter by more than a predetermined amount.
  • 11. The method of claim 10, including if the data value of the selected cell is indicated to be the first data value, then writing the first data value to the selected cell.
  • 12. A method for operating a memory device including an array of programmable resistance memory cells, and a sense amplifier coupled to the array which senses changes of voltage or current on a bit line coupled to a selected memory cell; the method comprising: reading the selected cell;measuring a time interval which correlates with resistance of the selected cell during said reading; andenabling a refresh process if the time interval has a duration that falls within a pre-specified range;said refresh process including determining a data value stored in the selected cell, and refreshing the data value in the selected cell, wherein the programmable resistance memory cells include phase change memory elements, having a set state corresponding to a first data value and a reset state corresponding to a second data value, and wherein said determining the data value stored in the selected cell includes storing a first resistance of the selected cell, setting the selected cell to the set state, measuring a set state resistance, resetting the selected cell to the reset state, measuring a reset state resistance, and indicating that the data value of the selected cell is the first data value if the first resistance is closer to the set state resistance than to the reset state resistance, else that the data value of the selected cell is the second data value.
US Referenced Citations (405)
Number Name Date Kind
3271591 Ovshinsky Sep 1966 A
3530441 Ovshinsky Sep 1970 A
3846767 Cohen Nov 1974 A
4452592 Tsai Jun 1984 A
4599705 Holmberg et al. Jul 1986 A
4719594 Young et al. Jan 1988 A
4769339 Ishii et al. Sep 1988 A
4876220 Mohsen et al. Oct 1989 A
4959812 Momodomi et al. Sep 1990 A
5106775 Kaga et al. Apr 1992 A
5166096 Cote et al. Nov 1992 A
5166758 Ovshinsky et al. Nov 1992 A
5177567 Klersy et al. Jan 1993 A
5332923 Takeuchi et al. Jul 1994 A
5391901 Tanabe et al. Feb 1995 A
5515488 Hoppe et al. May 1996 A
5534712 Ovshinsky et al. Jul 1996 A
5550396 Tsutsumi et al. Aug 1996 A
5687112 Ovshinsky Nov 1997 A
5688713 Linliu et al. Nov 1997 A
5716883 Tseng et al. Feb 1998 A
5754472 Sim et al. May 1998 A
5789277 Zahorik et al. Aug 1998 A
5789758 Reinberg Aug 1998 A
5814527 Wolstenholme et al. Sep 1998 A
5831276 Gonzalez et al. Nov 1998 A
5837564 Sandhu et al. Nov 1998 A
5869843 Harshfield Feb 1999 A
5879955 Gonzalez et al. Mar 1999 A
5902704 Schoenborn et al. May 1999 A
5920788 Reinberg Jul 1999 A
5933365 Klersy et al. Aug 1999 A
5952671 Reinberg et al. Sep 1999 A
5958358 Tenne et al. Sep 1999 A
5970336 Wolstenholme et al. Oct 1999 A
5985698 Gonzalez et al. Nov 1999 A
5998244 Wolstenholme et al. Dec 1999 A
6011725 Eitan Jan 2000 A
6025220 Sandhu Feb 2000 A
6031287 Harshfield Feb 2000 A
6034882 Johnson et al. Mar 2000 A
6046951 El Hajji et al. Apr 2000 A
6066870 Siek May 2000 A
6075719 Lowrey et al. Jun 2000 A
6077674 Schleifer et al. Jun 2000 A
6077729 Harshfield Jun 2000 A
6087269 Williams Jul 2000 A
6087674 Ovshinsky et al. Jul 2000 A
6104038 Gonzalez et al. Aug 2000 A
6111264 Wolstenholme et al. Aug 2000 A
6114713 Zahorik Sep 2000 A
6117720 Harshfield Sep 2000 A
6147395 Gilgen Nov 2000 A
6150253 Doan et al. Nov 2000 A
6153890 Wolstenholme et al. Nov 2000 A
6177317 Huang et al. Jan 2001 B1
6185122 Johnson et al. Feb 2001 B1
6188615 Perner et al. Feb 2001 B1
6189582 Reinberg et al. Feb 2001 B1
6236059 Wolstenholme et al. May 2001 B1
RE37259 Ovshinsky Jul 2001 E
6271090 Huang et al. Aug 2001 B1
6280684 Yamada et al. Aug 2001 B1
6287887 Gilgen Sep 2001 B1
6291137 Lyons et al. Sep 2001 B1
6314014 Lowrey et al. Nov 2001 B1
6316348 Fu et al. Nov 2001 B1
6320786 Chang et al. Nov 2001 B1
6326307 Lindley et al. Dec 2001 B1
6337266 Zahorik Jan 2002 B1
6339544 Chiang et al. Jan 2002 B1
6351406 Johnson et al. Feb 2002 B1
6372651 Yang et al. Apr 2002 B1
6380068 Jeng et al. Apr 2002 B2
6420215 Knall et al. Jul 2002 B1
6420216 Clevenger et al. Jul 2002 B1
6420725 Harshfield Jul 2002 B1
6423621 Doan et al. Jul 2002 B2
6429064 Wicker Aug 2002 B1
6438035 Yamamoto et al. Aug 2002 B2
6440837 Harshfield Aug 2002 B1
6462353 Gilgen Oct 2002 B1
6483736 Johnson et al. Nov 2002 B2
6487106 Kozicki Nov 2002 B1
6487114 Jong et al. Nov 2002 B2
6501111 Lowrey Dec 2002 B1
6511867 Lowrey et al. Jan 2003 B2
6512241 Lai Jan 2003 B1
6512263 Yuan et al. Jan 2003 B1
6514788 Quinn Feb 2003 B2
6514820 Ahn et al. Feb 2003 B2
6534781 Dennison Mar 2003 B2
6545903 Wu Apr 2003 B1
6551866 Maeda et al. Apr 2003 B1
6555860 Lowrey et al. Apr 2003 B2
6563156 Harshfield May 2003 B2
6566700 Xu May 2003 B2
6567293 Lowrey et al. May 2003 B1
6576546 Gilbert et al. Jun 2003 B2
6579760 Lung Jun 2003 B1
6584017 Maayan et al. Jun 2003 B2
6586761 Lowrey Jul 2003 B2
6589714 Maimon et al. Jul 2003 B2
6593176 Dennison Jul 2003 B2
6596589 Tseng et al. Jul 2003 B2
6597009 Wicker Jul 2003 B2
6605527 Dennison et al. Aug 2003 B2
6605821 Lee et al. Aug 2003 B1
6607974 Harshfield Aug 2003 B2
6613604 Maimon et al. Sep 2003 B2
6617192 Lowrey et al. Sep 2003 B1
6621095 Chiang et al. Sep 2003 B2
6627530 Li et al. Sep 2003 B2
6639849 Takahashi et al. Oct 2003 B2
6673700 Dennison et al. Jan 2004 B2
6674115 Hudgens et al. Jan 2004 B2
6677678 Biolsi et al. Jan 2004 B2
6744088 Dennison Jun 2004 B1
6750079 Lowrey et al. Jun 2004 B2
6750101 Lung et al. Jun 2004 B2
6762952 Munden et al. Jul 2004 B2
6768665 Parkinson et al. Jul 2004 B2
6781906 Perner et al. Aug 2004 B2
6791102 Johnson et al. Sep 2004 B2
6797979 Chiang et al. Sep 2004 B2
6800504 Li et al. Oct 2004 B2
6800563 Xu Oct 2004 B2
6815704 Chen Nov 2004 B1
6838692 Lung et al. Jan 2005 B1
6850432 Lu et al. Feb 2005 B2
6859389 Idehara Feb 2005 B2
6861267 Xu et al. Mar 2005 B2
6864500 Gilton Mar 2005 B2
6864503 Lung Mar 2005 B2
6867638 Saiki et al. Mar 2005 B2
6881603 Lai Apr 2005 B2
6888750 Walker et al. May 2005 B2
6894304 Moore May 2005 B2
6894305 Yi et al. May 2005 B2
6900517 Tanaka et al. May 2005 B2
6903362 Wyeth et al. Jun 2005 B2
6909107 Rodgers et al. Jun 2005 B2
6910907 Layadi et al. Jun 2005 B2
6927410 Chen Aug 2005 B2
6928022 Cho et al. Aug 2005 B2
6933516 Xu Aug 2005 B2
6936544 Huang et al. Aug 2005 B2
6936840 Sun et al. Aug 2005 B2
6937507 Chen Aug 2005 B2
6943365 Lowrey et al. Sep 2005 B2
6969866 Lowrey et al. Nov 2005 B1
6972428 Maimon Dec 2005 B2
6972430 Casagrande et al. Dec 2005 B2
6977181 Raberg et al. Dec 2005 B1
6992932 Cohen Jan 2006 B2
6998289 Hudgens et al. Feb 2006 B2
7023008 Happ Apr 2006 B1
7023009 Kostylev et al. Apr 2006 B2
7033856 Lung et al. Apr 2006 B2
7038230 Chen et al. May 2006 B2
7038938 Kang et al. May 2006 B2
7042001 Kim et al. May 2006 B2
7054183 Rinerson et al. May 2006 B2
7067837 Hwang et al. Jun 2006 B2
7067864 Nishida et al. Jun 2006 B2
7067865 Lung et al. Jun 2006 B2
7078273 Matsuoka et al. Jul 2006 B2
7085154 Cho et al. Aug 2006 B2
7099180 Dodge et al. Aug 2006 B1
7115927 Hideki et al. Oct 2006 B2
7122281 Pierrat Oct 2006 B2
7122824 Khouri et al. Oct 2006 B2
7126149 Iwasaki et al. Oct 2006 B2
7126847 Ha et al. Oct 2006 B2
7132675 Gilton Nov 2006 B2
7151273 Campbell et al. Dec 2006 B2
7154774 Bedeschi et al. Dec 2006 B2
7158411 Yeh et al. Jan 2007 B2
7164147 Lee et al. Jan 2007 B2
7166533 Happ Jan 2007 B2
7169635 Kozicki Jan 2007 B2
7190607 Cho et al. Mar 2007 B2
7202493 Lung et al. Apr 2007 B2
7208751 Ooishi et al. Apr 2007 B2
7214958 Happ May 2007 B2
7220983 Lung May 2007 B2
7229883 Wang et al. Jun 2007 B2
7238959 Chen Jul 2007 B2
7238994 Chen et al. Jul 2007 B2
7242618 Shappir et al. Jul 2007 B2
7248494 Oh et al. Jul 2007 B2
7251157 Osada et al. Jul 2007 B2
7253429 Klersy et al. Aug 2007 B2
7254059 Li et al. Aug 2007 B2
7262502 Chang Aug 2007 B2
7269052 Segal et al. Sep 2007 B2
7277317 Le Phan Oct 2007 B2
7291556 Choi et al. Nov 2007 B2
7309630 Fan et al. Dec 2007 B2
7314776 Johnson et al. Jan 2008 B2
7317201 Gutsche et al. Jan 2008 B2
7321130 Lung et al. Jan 2008 B2
7323708 Lee et al. Jan 2008 B2
7323734 Ha et al. Jan 2008 B2
7332370 Chang et al. Feb 2008 B2
7336526 Osada et al. Feb 2008 B2
7351648 Furukawa et al. Apr 2008 B2
7359231 Venkataraman et al. Apr 2008 B2
7364935 Lung et al. Apr 2008 B2
7365385 Abbott Apr 2008 B2
7379328 Osada et al. May 2008 B2
7385235 Lung et al. Jun 2008 B2
7388273 Burr et al. Jun 2008 B2
7394088 Lung Jul 2008 B2
7397060 Lung Jul 2008 B2
7400522 Toda et al. Jul 2008 B2
7423300 Lung et al. Sep 2008 B2
7426134 Happ et al. Sep 2008 B2
7440308 Jeong et al. Oct 2008 B2
7449710 Lung Nov 2008 B2
7473576 Lung Jan 2009 B2
7479649 Lung Jan 2009 B2
7485891 Hamann et al. Feb 2009 B2
7502252 Fuji et al. Mar 2009 B2
7505330 Pawlowski et al. Mar 2009 B2
7507986 Lung Mar 2009 B2
7514334 Chen et al. Apr 2009 B2
7514705 Breitwisch et al. Apr 2009 B2
7515461 Happ et al. Apr 2009 B2
7569844 Lung Aug 2009 B2
7764533 Breitwisch et al. Jul 2010 B2
7830701 Siau et al. Nov 2010 B2
20020017701 Klersy et al. Feb 2002 A1
20020070457 Sun et al. Jun 2002 A1
20020113273 Hwang et al. Aug 2002 A1
20020168852 Harshfield et al. Nov 2002 A1
20030072195 Mikolajick Apr 2003 A1
20030095426 Hush et al. May 2003 A1
20030116794 Lowrey Jun 2003 A1
20030186481 Lung Oct 2003 A1
20040026686 Lung Feb 2004 A1
20040051094 Ooishi Mar 2004 A1
20040113137 Lowrey Jun 2004 A1
20040165422 Hideki et al. Aug 2004 A1
20040248339 Lung Dec 2004 A1
20040256610 Lung Dec 2004 A1
20050018526 Lee Jan 2005 A1
20050029502 Hudgens Feb 2005 A1
20050052904 Cho et al. Mar 2005 A1
20050062087 Chen et al. Mar 2005 A1
20050093022 Lung May 2005 A1
20050127349 Horak et al. Jun 2005 A1
20050141261 Ahn Jun 2005 A1
20050145984 Chen et al. Jul 2005 A1
20050167656 Sun et al. Aug 2005 A1
20050191804 Lai et al. Sep 2005 A1
20050195633 Choi et al. Sep 2005 A1
20050201182 Osada et al. Sep 2005 A1
20050212024 Happ Sep 2005 A1
20050212026 Chung et al. Sep 2005 A1
20050215009 Cho Sep 2005 A1
20050263829 Song et al. Dec 2005 A1
20060006472 Jiang Jan 2006 A1
20060018156 Happ Jan 2006 A1
20060034112 Oh et al. Feb 2006 A1
20060038221 Lee et al. Feb 2006 A1
20060066156 Dong et al. Mar 2006 A1
20060073642 Yeh et al. Apr 2006 A1
20060091476 Pinnow et al. May 2006 A1
20060094154 Lung May 2006 A1
20060108667 Lung May 2006 A1
20060110878 Lung et al. May 2006 A1
20060110888 Cho et al. May 2006 A1
20060113520 Yamamoto et al. Jun 2006 A1
20060113521 Lung Jun 2006 A1
20060118913 Yi et al. Jun 2006 A1
20060124916 Lung Jun 2006 A1
20060126395 Chen et al. Jun 2006 A1
20060131555 Liu et al. Jun 2006 A1
20060138467 Lung Jun 2006 A1
20060154185 Ho et al. Jul 2006 A1
20060157680 Takaura et al. Jul 2006 A1
20060157681 Chen et al. Jul 2006 A1
20060158948 Fuji Jul 2006 A1
20060163554 Lankhorst et al. Jul 2006 A1
20060169968 Happ Aug 2006 A1
20060172067 Ovshinsky et al. Aug 2006 A1
20060175599 Happ Aug 2006 A1
20060192193 Lee et al. Aug 2006 A1
20060198183 Kawahara et al. Sep 2006 A1
20060202245 Zuliani et al. Sep 2006 A1
20060205108 Maimon et al. Sep 2006 A1
20060211165 Hwang et al. Sep 2006 A1
20060226409 Burr et al. Oct 2006 A1
20060234138 Fehlhaber et al. Oct 2006 A1
20060237756 Park et al. Oct 2006 A1
20060245236 Zaidi Nov 2006 A1
20060250885 Cho et al. Nov 2006 A1
20060261392 Lee et al. Nov 2006 A1
20060266993 Suh et al. Nov 2006 A1
20060284157 Chen et al. Dec 2006 A1
20060284158 Lung et al. Dec 2006 A1
20060284214 Chen Dec 2006 A1
20060284279 Lung et al. Dec 2006 A1
20060286709 Lung et al. Dec 2006 A1
20060286743 Lung et al. Dec 2006 A1
20060289847 Dodge Dec 2006 A1
20060289848 Dennison Dec 2006 A1
20070007613 Wang et al. Jan 2007 A1
20070008786 Scheuerlein Jan 2007 A1
20070030721 Segal et al. Feb 2007 A1
20070037101 Morioka Feb 2007 A1
20070040159 Wang Feb 2007 A1
20070051936 Pellizzer et al. Mar 2007 A1
20070096162 Happ et al. May 2007 A1
20070096248 Philipp et al. May 2007 A1
20070108077 Lung et al. May 2007 A1
20070108429 Lung May 2007 A1
20070108430 Lung May 2007 A1
20070108431 Chen et al. May 2007 A1
20070109836 Lung May 2007 A1
20070109843 Lung et al. May 2007 A1
20070111429 Lung May 2007 A1
20070115794 Lung May 2007 A1
20070117315 Lai et al. May 2007 A1
20070120104 Ahn et al. May 2007 A1
20070121363 Lung May 2007 A1
20070121374 Lung et al. May 2007 A1
20070126040 Lung Jun 2007 A1
20070131922 Lung Jun 2007 A1
20070138458 Lung Jun 2007 A1
20070140029 Kim et al. Jun 2007 A1
20070147105 Lung et al. Jun 2007 A1
20070153563 Nirschl Jul 2007 A1
20070154847 Chen et al. Jul 2007 A1
20070155172 Lai et al. Jul 2007 A1
20070156949 Rudelic et al. Jul 2007 A1
20070158632 Ho Jul 2007 A1
20070158633 Lai et al. Jul 2007 A1
20070158645 Lung Jul 2007 A1
20070158690 Ho et al. Jul 2007 A1
20070158862 Lung Jul 2007 A1
20070161186 Ho Jul 2007 A1
20070170881 Noh et al. Jul 2007 A1
20070173019 Ho et al. Jul 2007 A1
20070173063 Lung Jul 2007 A1
20070176261 Lung Aug 2007 A1
20070187664 Happ Aug 2007 A1
20070201267 Happ et al. Aug 2007 A1
20070215852 Lung Sep 2007 A1
20070224726 Chen et al. Sep 2007 A1
20070235811 Furukawa et al. Oct 2007 A1
20070236989 Lung Oct 2007 A1
20070246699 Lung Oct 2007 A1
20070249090 Philipp et al. Oct 2007 A1
20070252127 Arnold et al. Nov 2007 A1
20070257300 Ho et al. Nov 2007 A1
20070262388 Ho et al. Nov 2007 A1
20070267618 Zaidi et al. Nov 2007 A1
20070274121 Lung et al. Nov 2007 A1
20070285960 Lung et al. Dec 2007 A1
20070298535 Lung Dec 2007 A1
20080002464 Maayan Jan 2008 A1
20080006811 Philipp et al. Jan 2008 A1
20080012000 Harshfield Jan 2008 A1
20080014676 Lung et al. Jan 2008 A1
20080025089 Scheuerlein et al. Jan 2008 A1
20080043520 Chen Feb 2008 A1
20080094871 Parkinson Apr 2008 A1
20080101110 Happ et al. May 2008 A1
20080106923 Lung May 2008 A1
20080137400 Chen et al. Jun 2008 A1
20080138929 Lung Jun 2008 A1
20080138930 Lung Jun 2008 A1
20080138931 Lung Jun 2008 A1
20080164453 Breitwisch et al. Jul 2008 A1
20080165569 Chen et al. Jul 2008 A1
20080165570 Happ et al. Jul 2008 A1
20080165572 Lung Jul 2008 A1
20080166875 Lung Jul 2008 A1
20080179582 Burr et al. Jul 2008 A1
20080180990 Lung Jul 2008 A1
20080186755 Lung et al. Aug 2008 A1
20080191187 Lung et al. Aug 2008 A1
20080192534 Lung Aug 2008 A1
20080197334 Lung Aug 2008 A1
20080224119 Burr et al. Sep 2008 A1
20080225489 Cai et al. Sep 2008 A1
20080265234 Breitwisch et al. Oct 2008 A1
20080303014 Goux et al. Dec 2008 A1
20080310208 Daley Dec 2008 A1
20090001341 Breitwisch et al. Jan 2009 A1
20090014704 Chen et al. Jan 2009 A1
20090023242 Lung Jan 2009 A1
20090027950 Lam et al. Jan 2009 A1
20090042335 Lung Feb 2009 A1
20090057641 Lung Mar 2009 A1
20090072215 Lung et al. Mar 2009 A1
20090098678 Lung Apr 2009 A1
20090166603 Lung Jul 2009 A1
20090268507 Breitwisch et al. Oct 2009 A1
20090273968 Lamorey et al. Nov 2009 A1
20090289242 Breitwisch et al. Nov 2009 A1
20090294748 Breitwisch et al. Dec 2009 A1
20100214829 Breitwisch et al. Aug 2010 A1
Foreign Referenced Citations (1)
Number Date Country
2004025659 Mar 2004 WO
Non-Patent Literature Citations (55)
Entry
Wolf, Stanley, Excerpt from: Silicon Processing for the VLSI Era—vol. 4, pp. 674-679, 2004.
Wuttig, Matthias, “Towards a Universal Memory?” Nature Materials, Apr. 2005, pp. 265-266, vol. 4.
Yamada, Noboru, “Potential of Ge-Sb-Te phase-change optical disks for high-data-rate recording in the near future,” (Conference Proceedings Paper), Jul. 30, 1997, vol. 3109, 10 pages.
Yi, J. H. et al., “Novel Cell Structure of PRAM with Thin Metal Layer Inserted GeSbTe,” IEEE IEDM Dec. 10, 2003, 4 pages.
Yonehara, T. et al., “Control of Grain Boundary Location by Selective Nucleation Over Amorphous Substrates,” Mat. Res. Soc. Symp. Proc., vol. 106, 1998, pp. 21-26.
“Magnetic Bit Boost,” www.sciencenews.org, Dec. 18 & 25, 2004, p. 389, vol. 166.
“New Memories Tap Spin, Gird for Battle,” Science News, Apr. 3, 1999, p. 223, vol. 155.
“Optimized Thermal Capacitance in a Phase Change Memory Cell Design,” IPCOM000141986D, IP.com Prior Art Database, Oct. 18, 2006, 4pp.
“Remembering on the Cheap,” www.sciencenews.org, Mar. 19, 2005, p. 189, vol. 167.
“Thermal Conductivity of Crystalline Dielectrics” in CRC Handbook of Chemistry and Physics, Internet Version 2007, (87th edition), David R. Lide, ed. Taylor and Francis, Boca Raton, Fl, 2pp.
Adler, D. et al., “Threshold Switching in Chalcogenide-Glass Thin Films,” J. Appl/Phys 51(6), Jun. 1980, pp. 3289-3309.
Adler, David, “Amorphous-Semiconductor Devices,” Sci. Amer., vol. 236, pp. 36-48, May 1977.
Ahn, S. J. et al., “A Highly Manufacturable High Density Phase Change Memory of 64 Mb and Beyond,” IEEE IEDM Dec. 13-15, 2004, pp. 907-910.
Ahn, S. J. et al., “Highly Reliable 5nm Contact Cell Technology for 256Mb PRAM,” VLSI Technology, Digest of Technical Papers, Jun. 14-16, 2005, pp. 98-99.
Atwood, G, et al., “90 nm Phase Change Technology with u Trench and Lance Cell Elements,” VLSI Technology, Systems and Applications, Apr. 23-25, 2007, pp. 1-2.
Axon Technologies Corporation paper: Technology Description, published at least as early as Dec. 1997, pp. 1-6.
Bedeschi, F. et al., “4-MB MOSFET-Selected Phase-Change Memory Experimental Chip,” IEEE, Sep. 21 to 23, 2004, 4 PP.
Blake thesis, “Investigation of GeTeSb5 Chalcogenide Films for Use as an Analog Memory,” AFIT/GE/ENG/00M-04, Mar. 2000, 121 pages.
Chao, Der-Sheng, et al., “Low Programming Current Phase Change Memory Cell with Double GST Thermally Confined Structure,” Intl Symp on VLSI Technology, Systems and Applications, Apr. 23-25, 2007, pp. 1-2.
Chen, AN et al., “Non-Volatile Resistive Switching for Advanced Memory Applications,” IEEE IEDM, Dec. 5-7, 2005, 4 pp.
Cho, S. L. et al., “Highly Scalable On-axis Confined Cell Structure for High Density PRAM beyond 256Mb, ”Jun. 14-16, 2005 Symposium on VLSI Technology Digest of Technical Papers, pp. 96-97.
Gibson, G. A. et al., “Phase-change Recording Medium that Enables Ultrahigh-density Electron-beam Data Storage,” Applied Physics Letter, 2005, 3 pp., vol. 86.
Gill, Manzur et al., “A High-Performance Nonvolatile Memory Technology for Stand-Alone Memory and Embedded Applications,” Feb. 3-7, 2002 IEEE-ISSCC Technical Digest (TD 12.4), 7 pp.
Gleixner, “Phase Change Memory Reliability”, 22nd NVSMW, Aug. 26, 2007, 46 pages.
Ha, Y. H. et al., “An Edge Contact Type Cell for Phase Change RAM Featuring Very Low Power Consumption,” Jun. 10-12, 2003 Symposium on VLSI Technology Digest of Technical Papers, pp. 175-176.
Hanzawa, Satoru, et al., “A 512kB Embedded Phase Change Memory with 416kB/s Write Throughput at 100mA Cell Write Current,” ISSCC 2007, Session 26, Non-Volatile Memories/26.2, 3 pages.
Happ, T. D. et al., “Novel None-Mask Self-Heating Pillar Phase Change Memory,” 2006 Symposium on VLSI Technology, 2 pp.
Haring Bolivar, P. et al., “Lateral Design for Phase Change Random Access Memory Cells with Low-Current Consumption,” presented at 3rd E*PCOS 04 Symposium in Balzers, Principality of Liechtenstein, Sep. 4-7, 2004, 4pp.
Horii, H. et al., “A Novel Cell Technology Using N-doped GeSbTe Films for Phase Change RAM,” Jun. 10-12, 2003 Symposium on VLSI Technology Digest of Technical Papers, pp. 177-178.
Hudgens, S. et al., “Overview of Phase-Change Chalcogenide Nonvolatile Memory Technology,” MRS Bulletin, Nov. 2004, pp. 829-832.
Hwang, Y. N. et al., “Full Integration and Reliability Evaluation of Phase-change RAM Based on 0.24um-CMOS Technologies,” Jun. 10-12, 2003 Symposium on VLSI Technology Digest of Technical Papers, pp. 173-174.
Iwasaki, Hiroko et al., “Completely Erasable Phase Change Optical Disk,” Jpn. J. Appl. Phys., Feb. 1992, pp. 461-465, vol. 31.
Jeong, C. W. et al., “Switching Current Scaling and Reliability Evaluation in PRAM,” IEEE Non-Volatile Semiconductor Memory Workshop, Monterey, CA 2004, pp. 28-29 and workshop cover sheet.
Kim, Kinam et al., “Reliability Investigations for Manufacturable High Density PRAM,” IEEE 43rd Annual International Reliability Physics Symposium, San Jose, Apr. 17-21, 2005, pp. 157-162.
Kojima, Rie et al., “Ge-Sn-Sb-Te Phase-change Recording Material Having High Crystallization Speed,” Proceedings of PCOS 2000, pp. 36-41.
Lacita, A. L., “Electrothermal and Phase-change Dynamics in Chalcogenide-based Memories,” IEEE IEDM Dec. 13-15, 2004, 4 pp.
Lai, Stefan, “Current Status of the Phase Change Memory and Its Future,” IEEE IEDM Dec. 10, 2003, pp. 255-258.
Lai, Stephan et al., “OUM-A 180 nm Nonvolatile Memory Cell Element Technology for Stand Alone and Embedded Applications,” IEEE IEDM Dec. 2-5, 2001, pp. 803-806.
Lankhorst, Martijn H.R., et al; Low-Cost and Nanoscale Non-Volatile Memory Concept for Future Silicon Chips, Mar. 13, 2005, 6 pp., Nature Materials Advance Online Publication, www.nature.com/naturematerials.
Li, Yiming, “Temperature dependence on the contact size of GeSbTe films for phase change memories,” J. Comput Electron (2008) 7:138-141.
Mott, Nevill, “Electrons in Glass,” Nobel Lecture, Dec. 8, 1977, Physics, 1977, pp. 403-413.
Oh, Hyung-Rok, et al., “Enhanced Write Performance of a 64Mb Phase-Change Random Access Memory,” ISSCC 2005, Session 2, Non-Volatile Memory, 2.3, 3 pages.
Ovonyx Non-Confidential paper entitled “Ovonic Unified Memory,” Dec. 1999, pp. 1-80.
Ovshinsky, Sandford R., “Reversible Electrical Switching Phenomena in Disordered Structures,” Physical Review Letters, vol. 21, No. 20, Nov. 11, 1968, pp. 1450-1453.
Owen, Alan E. et al., “Electronic Conduction and Switching in Chalcogenide Glasses,” IEEE Transactions on Electron Devices, vol. Ed. 20, No. 2, Feb. 1973, pp. 105-122.
Pellizer, F. et al.,“Novel u Trench Phase-Change Memory Cell for Embedded and Stand-Alone Non-Volatile Memory Applications,” Jun. 15-17, 2004 Symposium on VLSI Technology Digest of Technical Papers, pp. 18-19.
Pirovano, Agostino et al.,“Reliability Study of Phase-Change Nonvolatile Memories,” IEEE Transactions on Device and Materials Reliability, Sep. 2004, pp. 422-427, vol. 4, No. 3.
Prakash, S. et al., “A guideline for Designing Chalcogenide-Based Glasses for Threshold Switching Characteristics,” IEEE Electron Device Letters, vol. 18, No. 2, Feb. 1997, pp. 45-47.
Radaelli, A. et al., “Electronic Switching Effect and Phase-Change Transition in Chalcogenide Materials,” IEEE Electron Device Letters, Oct. 2004, pp. 684-686, vol. 25, No. 10.
Rochefort, C. et al., “Manufacturing of High Aspect-Ration p-n Junctions Using Vapor Phase Doping for Application in Multi-Resurf Devices,” IEEE Jun. 4-7, 2002, pp. 237-240.
Schafft, Harry A. et al., “Thermal Conductivity Measurements of Thin Films Silicon Dioxide,” Proceedings of the IEEE 1989 International Conference on Microelectronic Test Structures vol. 2, No. 1, Mar. 1989, pp. 121-124.
Strauss, Karl F. et al., “Overview of Radiation Tolerant Unlimited Write Cycle Non-Volatile Memory,” IEEE Mar. 18-25, 2000, pp. 399-408.
Subramanian, Vivek et al., “Low Leakage Germanium-Seeded Laterally-Crystallized Single-Grain 100-nm TFT's for Vertical Integration Applications,” IEEE Electron Device Letters, vol. 20, No. 7, Jul. 1999, pp. 341-343.
Wicker, Guy et al., Nonvolatile, High Density, High Performance Phase Change Memory, 1999, http://klabs.org/richcontent/MAPLDCon99/Papers/P21—Tyson—P.PDF#search='nonvolatile%20high%20density%20high%20performance%20phase%20change%20memory', 8pages.
Wicker, Guy, “A Comprehensive Model of Submicron Chalcogenide Switching Devices,” Doctoral Dissertation, Wayne State University, Detroit, MI 1996, 137 pp.
Related Publications (1)
Number Date Country
20100321987 A1 Dec 2010 US