Patent Application
20050128927
Contact probe storage technology provides a method for ultrahigh density storage at a high speed. Most contact probe storage devices utilize arrays of cantilever beams with heated tips. The tips of the probes are kept in contact with a polymer media with a load determined by the bending of a cantilever beam on which the probe is supported. When heated sufficiently the probe can write data by locally fusing and forming pits in the media. Reading is carried out electrically by sensing a change in the impedance between the probe tip and a conducting layer below the media, or thermally by the change in the heat transfer characteristics when the probe tip is in a pit. The media is placed on a platform that can be moved in the x and y directions with respect to the tip or probe by a precision micromover.
One problem with cantilever devices of this type is the force needed to overcome the frictional forces resulting from all the cantilevers in continuous contact with the media. In addition, keeping the probe tips in continuous contact with the media results in tip wear.
The various aspects and features of the exemplary embodiment of the invention will become more clearly appreciated as a description of thereof is given with reference to the following drawings.
The embodiments of the invention relate to an actuator for contact probe storage device which is configured to undergo electrostatic actuation, so the probe tip can be drawn away from a medium and allowed to contact the media only when needed. The ability to selectively disengage the probe tip from the media when not reading or writing data substantially reduces the force required from the mover. If the probe tips are disengaged from the media when not in use, wear is significantly reduced.
In addition to actuation, the parallel plate electrodes which enable the electrostatic attraction also allow capacitive sensing of data.
Although only one probe actuator is shown in the drawings it will be understood that a plurality of these arrangements can be placed in an array with a 40 μm (for example) pitch, with multiplexing used to address specific probes.
An aluminum layer 118 is formed over the TaAl layer 116 to complete the heater 112. A recess is formed in the Al layer 118 to expose a portion of the TaAl layer 116. A probe 120 is formed on the TaAl layer in the illustrated manner.
As shown in
The flexures 104 and 108 also provide part of a circuit whereby the upper electrode 100, the lower electrode 102 and an air gap 122 therebetween, forms a capacitor which enables the change in distance between the upper and lower electrodes 100 and 102, which is induced by the probe 120 engaging a data indicative topographical feature, to be sensed.
The areas of the upper and lower electrodes 100, 102 are selected to minimize the mass, while providing adequate area for the parallel plate capacitor arrangement just mentioned. The gap between the fixed lower electrode 102 and the actuating upper electrode 100 is small to maximize the capacitance, but large enough to provide adequate displacement without pulling down when a voltage is applied across the upper and lower electrodes 100, 102.
As will be appreciated, although the upper and lower electrodes 100, 102 constitute an essential part of an actuator arrangement, they also constitute a part of a sensing arrangement which enables the change in distance to be detected during the periods the actuating voltage is not applied.
A spacer arrangement comprising spacers 124 are provided on the mounting portions 126 which support the free ends of the flexures 104-110. These spacers 124 have dimensions which are selected allow the probe 120 to protrude, when the flexures 104-110 are fully relaxed, above the upper level of the spacers 124 to a degree that disposition of a medium 128 (supported on a substrate or die 129) on the spacers 124 (in the manner shown in
This embodiment provides a high resonant frequency for fast operation. The stiffness of the flexures 104-110 are low enough to allow adequate z-axis displacement of the probe platform 100/112 at a reasonable voltage (e.g. 16 volt), while the load on the media from the suspension restoring force provided by the flexures 104-110 is within allowable limits. A suitable load is, merely by way of example, is 100 nN. This is based on current CPS devices is merely an example and in no way limiting as to load which can be selectively exerted.
An optimized device exhibits parameters which are summarized in the table below. The load on the probe tip when writing to media is near the desired target of 100 nN if the gap is set so that the probe tip is deflected 200 nm from the relaxed position. The voltage needed to pull down the probe tip ⅓ of the 900 nm gap is 16 volts.
The nominal capacitance is 1.3 fF. The difference in capacitance 0.2 fF is produced assuming a media film of 150 nm. Although small, this capacitance is of a detectable magnitude.
The fundamental frequency of the device is 300 kHz. However, this design could be optimized for a higher frequency by increasing the stiffness of the flexures and enable a target of 1 Mhz for example, to be achieved. Nevertheless, this would involve a tradeoff wherein increased load on the media and/or increased voltage needed to withdraw the probe 120 from contact with the medium 128.
Lowering the mass of the device could also increase the frequency. This, however, tends to lower capacitance and raise actuation voltage.
In
Next, as depicted in
This results in the arrangement illustrated in
In the event that the surface of the medium 128 is not smooth or free of data indicative topographical features as in the case illustrated in
This change in deflection can be detected through the change in capacitance between the upper and lower electrodes 100, 102. As shown in the above table, this change can be about 0.2 fF, which while being small is measurable and the change in deflection can be detected.
Although this invention has been described with reference to only a single embodiment, it will be understood that variants and modifications of the invention, which is limited only by the appended claims, will be readily envisaged by the person skilled in the art to which this invention pertains or most closely pertains, given the preceding disclosure. For example, as shown in
In the above type of arrangement, it is additionally possible for the heater/probe arrangement to carry out both imaging and reading using a thermomechanical sensing concept. The heater 112 can be used for writing and thermal readback sensing by exploiting a temperature-dependent resistance function. For writing the heater can be elevated to a temperature of 500-700° C. (for example).
For sensing, the heater 112 can be operated at about 200° C. This temperature is not high enough to soften the polymer medium which can consist of one more polymer layers including an upper layer of polycarbonate or polymethylmethacrylate (PMMA), but allows the molecular energy transfer between the structure on which the probe is carried, and the medium, to remove heat and thus provide a parameter which allows the presence/absence of a data indicative topographical feature to be detected.
