This application claims the benefit of Taiwan Patent Application No. 100124192, filed on Jul. 8, 2011, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of Disclosure
The present disclosure relates to a type of resistance random access memory and more particularly to a resistance random access memory featuring the characteristics of variable resistor and diode rectification by adjusting and controlling the energy barrier through voltage.
2. Related Art
Referring to
Generally, memory is often structured to form memory array.
Therefore, a resistor element 10 is often used with a transistor 13 to form a 1T1R structure as shown in
The present disclosure of a type of resistance random access memory (RRAM) structure having the function of diode rectification includes a first electrode, a second electrode and a resistance conversion layer. The resistance conversion layer is disposed between the first electrode and the second electrode; and it includes a first oxidized insulating layer which is adjacently connected to the first electrode; a second oxidized insulating layer which is adjacently connected to the second electrode; as well as an energy barrier turning layer disposing between the first oxidized insulating layer and the second oxidized insulating layer. Energy barrier high can be adjusted and controlled to change the resistance by voltage between the energy barrier turning layer and the first oxidized insulating layer A fixed energy barrier is formed between the second oxidized insulating layer and the energy barrier turning layer, so that the resistance random access memory element features the function of diode rectification.
The present disclosure will become more fully understood by reference to the following detailed description thereof when read in conjunction with the attached drawings.
Referring to
Wherein, the first electrode 21 can be a type of conductor or semi-conductor including the conducting materials of platinum, gold, aluminum, titanium, tungsten, ruthenium, tantalum, titanium nitride or silicon. The second electrode 22 is made of silicon-based material (N+ Si) with arsenium ions, or is a type of conductor or semi-conductor including the conducting materials of platinum, gold, aluminum, titanium, tungsten, ruthenium, tantalum, titanium nitride or silicon.
Oxide materials of the first oxidized insulating layer 31 including oxides of silicon, hafnium, aluminum, zirconium, niobium, titanium, tantalum and lanthanum, for examples, oxides in stoichiometric ratio such as SiO2, HfO2, Al2O3, ZrO2, NbO, TiO2, NiO, Ta2O5 and La2O3, or other similar oxides, but not limited to the above-mentioned oxides. The second oxidized insulating layer 32 adopts the same oxide elements as used in the first oxidized insulating layer 31, or different oxide elements as required by designers.
The energy barrier turning layer 33 adopts a silicon nitride layer (a chemical compound of silicon and nitrogen) in stoichiometric ratio with energy gaps which can be increased by increasing the oxygen ratio. The silicon nitride layer also includes silicon, germanium, germanium-oxygen compound (GeN), or metallic oxides with excess metals. In this embodiment, silicon nitride (Si3N4) is used as an example but is not limited to it, as required otherwise by designers.
According to the structure of the resistance conversion layer 30, an energy barrier is formed between the energy barrier turning layer 33 and the first oxidized insulating layer 31; a fixed energy barrier is formed between the energy barrier turning layer 33 and the second oxidized insulating layer 32.
It should be noted that the energy barrier mentioned here refers to the barrier in electron transport, but not the energy barrier of the combination of molecules. Wherein, when a bias voltage (Vb) is applied across the first electrode 21 and the second electrode 22, the resistance conversion layer 30 will feature the characteristics of a variable resistor or diode depending on the voltage polarity. When the resistance conversion layer 30 shows the characteristics of a variable resistor; the afore-mentioned energy barrier high can be adjusted by the interaction of the energy barrier turning layer 33 and the first oxidized insulating layer 31; so that the resistance of the resistance random access memory can be adjusted. The activation of generating process for resistance random access memory, and the operating of variable resistor characteristics and diode characteristics are explained below.
A formation voltage (Vf) is applied across the first electrode 21 and the second electrode 22, the second electrode 22 is grounded and a voltage of negative 30 volts (−0V) is applied to the first electrode 21. This operation process causes the soft breakdown of the first oxidized insulating layer 31 and a local conductive path 34 is formed. Wherein, the bonds of oxygen ions (O−2) 35 of the first oxidized insulating layer 31 are broken and are able to interact with the elements (Si and N) of the energy barrier turning layer 33 to form a local energy barrier turning layer (SiONx) 36.
A negative bias voltage (Vb) is applied across the first electrode 21 and the second electrode 22. Under the assistance of suitable electric field conditions and the local conductive path 34, the oxygen ions 35 of the first oxidized insulating layer 31 interact and combine with the elements of the energy barrier turning layer 33 (formation of SiONx) in the local interface of the first oxidized insulating layer 31 and the energy barrier turning layer 33. In the partial energy barrier turning layer 36, the oxygen level in SiONx formed with Si3N4 can affect the energy barrier high. Thus the energy barrier high between the first oxidized insulating layer 31 and the energy barrier turning layer 33 would different after applying the voltage. But the energy barrier high (for the fixed energy barrier) between the second oxidized insulating layer 32 and the energy barrier turning layer 33 remains the same.
In other words, the energy barrier high is controlled by the interaction intensity of combination and detachment of oxygen ions of the first oxidized insulating layer 31 and the elements of the energy barrier turning layer 33. Yet, the interaction intensity of combination and detachment is controlled by the volts of either a positive or a negative voltage. Therefore, the resistance of the resistance random access memory can be adjusted by changing the energy barrier high, in order to be applied in data memory.
A positive bias voltage Vb is applied across the first electrode 21 and the second electrode 22. An electron flows sequentially from the second electrode 22, the second oxidized insulating layer 32, the energy barrier turning layer 33, the first oxidized insulating layer 31 and then to the first electrode 21.
However, there are two problems related to energy for movement of the electron. Firstly, the energy barrier between the second oxidized insulating layer 32 and the second electrode 22. Secondly, the energy difference of conductive band between the energy barrier turning layer 33 and the second electrode 22. In other words, although the bias voltage Vb provides more energy for the electron e, the energy level of electron e must be equal to or higher than the afore-mentioned energy difference of conductive band, in order to have a chance to pass through the second oxidized insulating layer 32 and reaches the first electrode 21. In other words, the current in the resistance random access memory will be limited once the energy level of electron e is lower than the afore-mentioned energy difference of conductive band. This type of working mode is the mechanism of rectification. The bias voltage to enable electrons to possess more energy than the energy difference of conductive band is the cut-in voltage (shown as Vcut-in in
According to the ways of bias voltage supply as shown in
Note that the specifications relating to the above embodiments should be construed as exemplary rather than as limitative of the present disclosure, with many variations and modifications being readily attainable by a person of average skill in the art without departing from the spirit or scope thereof as defined by the appended claims and their legal equivalents.
Number | Date | Country | Kind |
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100124192 | Jul 2011 | TW | national |