Patent Application
20080310052
This invention relates to the utilization of ferroelectric materials in a disk drive, in particular to a ferroelectric disk, a ferroelectric disk drive accessing the ferroelectric disk, and a slider electrically coupled to the ferroelectric disk.
The invention involves a new material used for a disk in a new disk drive, based upon the ferroelectric effect. Before summarizing the invention, this section will review two primary memory storage architectures and then review the most current research pointing to the invention. A third primary memory architecture involving tape drives is not discussed because it is not seen as relevant to this invention.
A hard disk drive implements the first memory architecture, which stems from the inventions of Thomas Edison, and involves a rotating surface, over which an actuator positions a sensor, which may also include a writing device. Starting with the gramophone in the late nineteenth century, it has evolved into the modern optical disk drive, removable media disk drives, as well as the hard disk drive, which collectively hold the record for the greatest density of information at the lowest cost per bit, and have throughout most of their history. This architecture tends to support access of data in long strings, often arranged as closed tracks on the rotating surface. Conventional hard disk drives currently operate at a storage density of 133 gigabits per square inch using ferromagnetic memory cells.
The second memory architecture stems from the invention of arrays of memory cells arranged to be accessed in a much smaller unit, often called a byte or word. It was implemented with ferromagnetic core memories by mid twentieth century, and evolved into today's flash memory, dynamic and static RAM devices. These tend to serve computers as random access devices or serve as media storage devices emulating disk drives. They have been at the forefront in providing rapid access of data in essentially random addressing patterns.
By way of comparison memory cell arrays emulating disk drives have tended to have smaller overhead, in that typically a column is accessed at a time. The columns tend to be a fixed length string of bits used like a sector on a disk drive.
Finally, there is considerable interest in using ferroelectric materials for memory applications, known as ferroelectric memory devices. These devices are known for being non-volatile with very high write-erase cycling before failure. Ferroelectric memory cells on the order of nanometers are believed feasible. Today, the typical application of this memory technology is in a Ferroelectric Random Access Memories, or FRAMs, a memory cell array. Typically, the FRAM is an array of ferroelectric capacitors arranged in cells similar to Dynamic RAM (DRAM) cells, except that the dielectric layer of the DRAM cell is replaced with a ferroelectric film, often composed of ferroelectric material such as lead zirconate titanate. While in general similar to the capacitors used in DRAM cells, the ferroelectric film retains an electric field after the charge in the capacitor drains, making it non-volatile. These cells can be written in under 100 nanoseconds (ns), making them as fast to write as to read and much faster to write than other contemporary non-volatile semiconductor memory cells. Their manufacturing process typically involves two additional masking steps when compared to normal semiconductor manufacturing processes.
An article entitled “Scanning resistive probe microscopy: Imaging ferroelectric domains” by Park, et. al. in the Applied Physics Letters Volume 84, number 10, pages 1734-1736 reports verifying a resistive probe that could detect a ferroelectric domain at high speed and be used as a read-write head in a resistive probe data storage system, which is incorporated herein by reference. While this research is fundamental and necessary, there remain significant problems to be solved.
The reported current sensitivity of the resistive probe “[IR(VG=1 V)-IR(VG=0 V)]/IR(VG=0 V)” was measured to be 0.3% to 0.5%. The resistive probe signal will need to travel on the order of 4 centimeters (cm), making it necessary to deal with transmission noise at its destination. Methods and apparatus are needed that strengthen resistive probe sensitivity before transmission.
The article reports asserting 30 volts between the resistive probe site and the electrode on the other side of the ferroelectric film to alter the electric field in a first direction and asserting −30 volts to alter the electric field in a second, opposite direction. This poses a second problem, suppose that the bits to be written on a ferroelectric disk were 5 nanometers (nm) apart, that the ferroelectric disk was 75 millimeters wide and rotates at 6000 revolutions per minute. Assume that a track has a diameter of 75 mm and is written with data for every bit it can hold in one revolution. This works out to roughly 47 Million bits written in 1 part of 6000 of a minute, or one hundredth of a second. Put another way, an alternating current signal at a frequency of over one Gigahertz with amplitude of 30 Volts needs to be provided, again transmitted over the 4 centimeters. This may pose serious problems with inductive coupling and noise. Methods and apparatus are needed to minimize the inductive effects associated with writing data to a track on a ferroelectric disk.
Also in the article, there is a discussion of how the resistive probe was used to polarize the ferroelectric domain. A voltage was applied between the resistive tip of the resistive probe and an electrode of the ferroelectric film to polarize the ferroelectric domain. Applying the voltage to an electrode of a ferroelectric domain measuring 37 cm in radius may bring with it problems. The ferroelectric film is essentially a capacitor, as mentioned earlier. Methods and apparatus are needed for sharing the electrode and/or supporting ferroelectric domains of limited surface area.
U.S. Pat. No. 6,515,957 “Ferroelectric drive for data storage,” discloses a ferroelectric disk drive using two transducers, one for reading and one for writing operations. The write transducer is a sharp, electrically conductive tip, closely spaced adjacent to the magnetic medium for the write operation. The read transducer is a field effect transducer, which also must be spaced close to the media to resolve the written ferroelectric domains. It is unclear at this time whether the read transducer may not suffer similar limitations to the read head of conventional hard disk drives, which may well limit their usefulness with ferroelectric cells at or below 50 nm pitch.
Conventional hard disk drives operate at storage density 133 Gigabits per square inch. One future goal is to record at one thousand gigabits per square inch or 1 Terabit (Tb) per square inch. This density may be achieved, for example, if bits are recorded in a square matrix at a 50 nanometer pitch, which appears beyond the capabilities of the ferromagnetic cells used in these hard disk drives. A new disk drive is needed to reach this target storage density.
One embodiment of the invention is a ferroelectric disk drive including at least one embodiment of a ferroelectric disk attached by at least one disk mounting component to a spindle motor. The ferroelectric disk includes at least one electrode sheet buried beneath a resistive probe surface with an electrode coupling through the disk mounting component to create an electrode path to a slider in the head stack assembly. The electrode path forms an electrical circuit between the electrode sheet and a resistive probe in the slider accessing the state of a ferroelectric cell retained by a ferroelectric film situated between the resistive probe surface and the electrode sheet. The disk mounting components may include a disk mount, a disk clamp, and/or possibly one or more disk spacers. The resistive probe surface may preferably include a layer of lubricant over a layer of Diamond Like Carbon (DLC) over the ferroelectric film. The resistive probe may preferably make contact with the lubricant without penetrating it, thereby avoiding solid-to-solid contact with the DLC layer.
A method of the invention accesses data on the disk surface of the ferroelectric disk, through reading and writing a track on the disk surface by providing voltages between resistive probe sites through the electrode path between the slider and the electrode sheet, for the ferroelectric cell of each bit in the track. The invention includes the bit values of the bits in the track, as a product of the access process.
Another embodiment of the invention is a slider including an electrical coupling to the electrode path to the electrode sheet, a resistive probe contacting the resistive probe surface to provide a voltage to the probe site of the ferroelectric cell with respect to the electrode sheet and an amplifier sensing the current through the resistive probe to create an amplified read signal. The amplifier acts to increase the sensitivity of the resistive probe and reduce the transmission noise effects on the amplified read signal.
Three other embodiments of the invention are assemblies of the slider: a head gimbal assembly, a head stack assembly and a ferroelectric disk drive, each include an embodiment of the slider and provide the electrode path between at least one electrode sheet to the amplifier in the slider for accessing data stored in ferroelectric cells on at least one disk surface of a ferroelectric disk.
This invention relates the utilization of ferroelectric materials in a disk drive, in particular to a ferroelectric disk, a ferroelectric disk drive accessing the ferroelectric disk, and a slider receiving an electrode path electrically coupled the electrode sheet of the ferroelectric disk and using an amplifier to sense a current between a resistive probe and the electrode path.
Several embodiments of this invention act at different levels to create the claimed embodiments of a ferroelectric disk drive 10. Before entering a more detailed discussion, here is an outline of the components and their interactions: The ferroelectric disk drive includes at least one embodiment of a ferroelectric disk 12 as shown in
The voice coil motor 36 includes a voice coil 32 coupled to the head stack assembly 52, which is mounted by the actuator pivot 30 to the disk base 16 so that the head stack assembly rotates through the actuator pivot in response to the interaction between the voice coil and the fixed magnet assembly 34. The head stack assembly includes at least one actuator arm 28 coupled to at least one embodiment of a head gimbal assembly 26. The head gimbal assembly includes an embodiment of the slider 20, which is positioned near a track 22 on the rotating disk surface 4.
In many embodiments of the ferroelectric disk drive 10, a control circuit 50 stimulates the spindle motor to rotate the ferroelectric disk, creating the rotating disk surface 4. The control circuit may further stimulate the voice coil 32 to cause the voice coil motor 36 to position the slider 20 near the track 22. Some embodiments of the ferroelectric disk drive 10 may include a printed circuit board assembly 38, which may be driven by the control circuit to stimulate the voice coil and/or the spindle motor.
In some embodiments of the ferroelectric disk drive 10, the head stack assembly 52 may include one actuator arm 28 as shown in
Both embodiments of the ferroelectric disk drive 10, the head gimbal assembly 26 and the head stack assembly 52, provide the electrode path 80 between the electrode sheet 90 and the slider 20, which is also included in these embodiments.
Operating the ferroelectric disk drive 10 may include the following. The spindle motor 14 is directed by the control circuit 50 through a rotation control signal 42 to rotate the ferroelectric disk 12, preferably bringing it up to a nearly constant rotational velocity. The electrode coupling 90 of the disk surface 4 electrically couples through at least one of the disk mounting components to create the electrode path 80 provided to the slider 20. Accessing the data of the track 22 includes stimulating the voice coil 32 with a position control signal 40 delivered as a time varying electric signal to the voice coil, which interacts with the fixed magnet 34 to alter the lateral position of the slider until it is near the track. The control circuit may directly present the position control signal or stimulate a motor control interface to drive the voice coil motor. Once the slider is close to the track, the ferroelectric disk drive enters a track following mode. A micro-actuator assembly 70 may be employed during track following and possibly also during the track seek operation. During track following mode, the read-write signal bundle may stimulate a preamplifier included in the head stack assembly 52 to at least partly create the read-write signals received by the control circuit, in particular by a processor communicating through a channel interface to access the data in the track on the rotating disk surface.
Data stored on the disk surface 4 of the ferroelectric disk 12 may preferably be accessed through reading and writing the track 22 on the disk surface by providing voltages between resistive probe sites and the electrode sheet 90, for the ferroelectric cell of each bit in the track as shown in
The electrode sheet 90 may be deposited on a disk substrate 120. The disk substrate may include a glass disk substrate and or a metallic disk substrate similar to those used in contemporary ferromagnetic disks for hard disk drives. The electrode sheet may include at least one conductive metal. For the purpose of clarity, the application will speak of the electrode sheet and the disk substrate as distinct, however there may be embodiments where they are essentially the same.
The ferroelectric film 92 may include a concentration, essentially consisting of the group of elements in a mixture: lead (Pb), zirconium (Z), titanium (Ti), and oxygen (O). These elements may further form a compound, and the ferroelectric film may preferably include the Pb(Zr0.4Ti0.6)O3 compound. The concentration may preferably be at least ninety percent of the molecular weight of the ferroelectric film.
The disk surface 4 of the ferroelectric disk 12 may include at least two instances of the ferroelectric cell 100 in the track 22, as shown in
At least two ferroelectric cells 100 may share an electrode sheet 90. In certain embodiments, the ferroelectric cells of a sector may share a single electrode sheet, which may or may not be shared with other sectors in a track 22. The electrode sheet may be shared by all the sectors of a track but not with all tracks of a disk surface 4. In other embodiments, all the ferroelectric cells of all the bits accessed through the tracks of one disk surface may share a single electrode sheet as shown in
Some of the embodiments of the ferroelectric disks 12 include at least one electrode sheet 90 buried beneath a resistive probe surface with one or more electrode couplings 122 through the disk mounting component 82, 84 and/or 86 to create an electrode path 80 through the ferroelectric disk drive 10 to a slider 20 in the head stack assembly 52.
The ferroelectric disk 12 including the first disk surface 4 preferably provides multiple tracks of ferroelectric cells, each track 22 organized as multiple sectors, with each sector including at least one ferroelectric cell 100, preferably arranged as a payload of N ferroelectric cells and an envelope of M ferroelectric cells, where N is typically a power of two, often at least 2̂8=256, and M is sufficient for the envelope to function as the coding overhead for an error correcting/detecting coding scheme. Each ferroelectric cell includes a probe site 102 on the ferroelectric film 92.
A ferroelectric domain preferably includes at least two ferroelectric cells 100 sharing an electrode sheet 90. Each ferroelectric cell may sustain its electric field direction in a non-volatile manner. There may be more than one ferroelectric domain on a disk surface. To simplify the discussion, only a single ferroelectric domain will be shown and discussed hereafter. This is being done to simplify the discussion and not to limit the scope of the invention.
Another embodiment of the invention is a head gimbal assembly 26 including one of these sliders 20, providing the electrode path 80 to the slider as shown in
The amplifier 170 of
The resistive probe 24 preferably operates as follows. The resistive region 114 is much higher in resistance than the highly doped regions 110, it acts as a small resistor at the tip of the resistive probe. When the tip approaches the ferroelectric material, electrons, as the majority carriers in the resistive region are depleted by the electric field from the negative surface charges. The depletion of the majority carriers alters the volume of the conducting path of the resistive region, resulting in a resistance change.
Alternatively, the majority carriers may be accumulated in the resistive region by the second electric field 118 from the positive surface charges as shown in
These changes in resistance in the resistive probe 24 may alter the sensed current 174 in the slider 20. This sensed current is then amplified offset by the electrical coupling of the electrode path 80 to generate the amplified read signal 184.
Accessing data stored on a disk surface 4 will be discussed by an example using a track 22 on the disk surface 4 as shown in
In certain embodiments of the invention, the slider 20 may further include a vertical micro-actuator 190 at least partly controlling the contact pressure of the resistive probe 20 on the rotating disk surface 4. The vertical micro-actuator may employ a thermal mechanical effect, a piezoelectric effect and/or an electro-static effect.
The resistive probe 24 is preferably conical in shape and includes the resistive region 114 composed of the low doped n+ type material electrically coupled to the p-type region 112 and in certain embodiments, preferably connected to metal pads on a cantilever 72 through highly doped n-type regions 110 on the incline, which electrically couples the resistive probe to the amplifier 170.
In certain embodiments, a Position Error Signal may be provided to the control circuit 50 of
Manufacturing the ferroelectric disk drive 10 may include assembling a ferroelectric disk stack including the spindle motor 14, at least one of the disk mounting components 82, 84, and 86 with, at least one of the ferroelectric disks 12, assembling a head stack assembly 52, mounting the ferroelectric disk stack onto a disk base 14, rotatably coupling the head stack assembly through the actuator pivot 58 to the disk base and aligning it with the fixed magnets 34 to create the voice coil motor 30, coupling the control circuit 50 to the voice coil motor and the disk base, and to the ferroelectric disk stack to create a partly assembled ferroelectric disk drive. The disk cover 16 may be mounted over the partly assembled ferroelectric disk drive to create the ferroelectric disk drive 10.
The preceding embodiments provide examples of the invention and are not meant to constrain the scope of the following claims.
This application claims priority to U.S. Provisional Patent Application No. 60/934,853, filed Jun. 15, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60934853 | Jun 2007 | US |
