Patent Application
20070292652
This invention relates the utilization of ferroelectric materials in a disk drive, in particular to a ferroelectric disk, the slider, head gimbal assembly, head stack assembly, and a ferroelectric disk drive accessing the ferroelectric disk.
The invention's ferroelectric disk 12 is for use in at least a ferroelectric disk drive 10 and includes a first disk surface 120-1 and a second disk surface 120-2. The first disk surface includes at least one ferroelectric film 126 electrically coupled to a probe surface 124 facing away from the ferroelectric disk and sharing an electrode sheet 128 with a ground coupling 136. The ground coupling may preferably be presented to a disk clamp 131 and/or a disk mount 129 and/or a disk spacer 134 to provide a coupling to a ground shared with the slider 90, as shown in
The invention includes the following method of accessing data 122 stored on a disk surface, for example, the first disk surface 120-1. A first voltage is provided between a probe site 132 on the probe surface 124 and the ground coupling 136, causing a ferroelectric cell 130 approximating the vertical footprint of the probe site to sustain a first electric field direction E1, as shown in
The ferroelectric film 126 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 first disk surface 120-1 of the ferroelectric disk 12 includes at least two instances of the ferroelectric cell 130, for example as shown in
The ferroelectric disk 12 including the first disk surface 120-1 preferably provides multiple tracks of ferroelectric cells, each track 122 organized as multiple sectors, with each sector including at least one ferroelectric cell 130, 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 132 on the ferroelectric film 126.
The ferroelectric disk 12 operates as follows: for each ferroelectric cell 130, providing a first voltage between said probe site 132 and said ground coupling 136 causes said ferroelectric cell to sustain a first electric field direction E1. Providing a second voltage between said probe site and said ground coupling causes said ferroelectric cell to sustain the second electric field direction E2 essentially opposite said first electric field direction, where said second voltage is opposite said first voltage in sign. The ferroelectric cell sustains its electric field in a non-volatile manner, where the cell does not have to receive energy or power to sustain its electric field direction. Applying a third voltage between the probe site and the ground coupling to measure a memory current Im indicates whether the ferroelectric cell sustains the first electric field direction, or sustains the second electric field direction.
The invention's head gimbal assembly 60 includes a slider 90 including a resistive probe 94 capable of sensing the electric field near the probe site 132 of the ferroelectric cell 130 of a track 122 on a disk surface with respect to a ground shared through the ground coupling 136 with the invention's ferroelectric disk 12 to create the memory current Im provided to an amplifier 96, which provides an amplified read signal Ar0 when used to read the data contained in the track. The amplifier acts to increase the sensitivity of the probe and reduce the transmission noise effects on the amplified read signal. The head gimbal assembly preferably includes a micro-actuator assembly 80 coupled to the resistive probe to aid in laterally positioning Lp the resistive probe close to the track.
The resistive probe 94 is preferably conical in shape, as shown in
The resistive probe 94 operates as follows. The resistive region 94-3 is much higher in resistance than the highly doped regions 94-1, 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 E1 from the negative surface charges as shown in
Alternatively, the majority carriers are accumulated in the resistive region by the second electric field E2 from the positive surface charges as shown in
As used herein, a micro-actuator assembly 80 may use a piezoelectric effect PZT as shown in
The ferroelectric disk drive 10 may include more than one ferroelectric disk, as shown in
In certain embodiments, the ground coupling 136 of the first disk surface 120-1 may be shared with the second disk surface 120-2 and/or both disk surfaces may have a ground coupling shared with the other disk surface.
The invention includes an actuator arm 52 coupling to a first head gimbal assembly 60 for access to the first disk surface 120-1 as shown in
The invention includes a head stack assembly 54 with an actuator arm 52 coupling to a first head gimbal assembly 60 for access to the first disk surface 120-1. The head stack assembly may further couple to a second head gimbal assembly 60-2 for access to the second disk surface 120-2 as shown in
The slider 90 and/or the head gimbal assembly 60 may further preferably include a vertical micro-actuator 98 for altering the vertical position VP of the resistive probe 94 off the disk surface. The ferroelectric disk drive 10 may operate by stimulating the vertical micro-actuator to decrease the vertical position of the resistive probe over the sector and increase the vertical position over the shared contact gap.
In further detail, a head gimbal assembly 60 preferably includes a load beam 74 mechanically coupling through a hinge 70 to a base plate 72, which is coupled to an actuator arm 52, often using a swaging process. The slider 90 is mechanically coupled to the micro-actuator assembly 80, both of which coupled to a flexure finger 20. The flexure finger preferably provides the read-write signal bundle rw between the slider and its amplifier 96, which acts as an interface to the resistive probe 94. The flexure finger is typically coupled to the load beam.
The head stack assembly 50 includes the head stack 54 containing at least one actuator arm 52, as shown in
The head stack assembly 50 further includes a voice coil 32 rigidly coupled through the head stack 54 and its actuator arm 52 to the head gimbal assembly 60. The ferroelectric disk drive 10 further includes the head stack assembly 50 rotatably coupled through an actuator pivot 58 to the disk base 14 and positioned near at least one fixed magnet 34 and aligned so that the head gimbal assembly can be laterally positioned LP over the disk surface, shown in the Figures as the first disk surface 120-1 of the ferroelectric disk 12. The voice coil motor 18 includes the head stack assembly, fixed magnet and disk mounted to the spindle shaft 40 of the spindle motor 270.
Operating the ferroelectric disk drive includes the following. The spindle motor 270 is directed by the embedded circuit 500 to rotate the ferroelectric disk 12, preferably bringing it up to a nearly constant rotational velocity. The ground coupling 136 of the first disk surface 120-1 electrically couples through at least one of the disk mount 129, the disk clamp 131 and/or a disk spacer 134 sharing a ground provided to the slider 90 and its amplifier 96. Accessing the data of a track 122 includes stimulating the voice coil 32 with a voice coil control signal 22 delivering a time varying electric signal to the voice coil, which interacts with the fixed magnet to alter the lateral position LP of the slider until it is near the track. The voice coil control signal is provided by a voice coil driver 30 included in the embedded circuit. While the micro-actuator assembly may be employed during this track seek operation, it most significant once the slider is close to the track, which is often referred to as the track following mode. During track following mode, the read-write signal bundle rw stimulates a preamplifier 24 to at least partly create the read-write signals 25, in particular the read signal 25-R, which is received by the channel interface 26. The channel interface may preferably provides a Position Error Signal 650 to a servo controller 600, which may preferably be responsible for stimulating the voice coil motor and the micro-actuator assembly 80 to control the lateral position of the resistive probe to keep it near the track.
The servo controller 600 may preferably include a servo computer 610 accessibly coupled 612 a servo memory 620, in which a program system 1000 resides as a collection of program steps.
Consider the second problem posed by the prior art. Again 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 for the sake of discussion that a track has a circumference of 75 mm. The high voltage swings in certain embodiments may be handled by writing at a lower speed than reading. By way of example, providing the third voltage between the probe site 132 and the ground coupling 136 to read the bit value from the bit may be performed at a read-rate and providing the voltage to write the bit value into the bit may be performed at a fraction of the read-rate, where the fraction is less than one. By way of a further example, writing the track 122 may be performed in more than one revolution, say K revolutions. This works out to roughly 150 Million bits written in K parts of 6000 of a minute, or K hundredths of a second. Put another way, an alternating current signal at a frequency of over one Gigaherz divided by K with an amplitude of 30 Volts needs to be provided, again transmitted over the 10 to 30 centimeters. K may be preferred to be essentially an integer, for example, perhaps 2, 3, 4, and so on.
The preceding embodiments provide examples of the invention and are not meant to constrain the scope of the following claims.
