EP1839304A1 - Device for recording data, comprising a peripheral support membrane, and method for producing the same - Google Patents

Abstract

The invention relates to a device for recording data, said device comprising a two-dimensional network of microdots (2) with nanometric dimensions, facing a storage medium. The storage medium comprises a sensitive area preferably provided with a membrane (4) which is flexible and extended at the periphery thereof by a flexible fixing membrane (6). The sensitive area of the storage medium is thus elastically fixed to an external frame (3), authorising a displacement of the sensitive area in the plane thereof and perpendicularly to the plane thereof. The microdots (2) are preferably formed on a front convex face of a substrate (8), enabling the contact between each of the microdots and the sensitive area to be ensured at all times. The curve radius of the convex surface is preferably between 0.5m and 5m.

Description

Data recording device comprising a peripheral support membrane and method of manufacture

Technical field of the invention

The invention relates to a data recording device comprising a two-dimensional network of micro-tips, of nanometric dimensions, arranged facing a memory medium and means for elastic fastening of a sensitive area of the memory medium on an external frame. , allowing a displacement of said sensitive zone in its plane.

The invention also relates to a method of manufacturing such a device.

State of the art

In the field of data recording, very large storage capacities have recently been obtained by implementing networks of micro-points, whose apex is of nanometric dimension. An actuator, which may be electromechanical, allows a monolithic relative displacement of the entire micro-tip array with respect to the surface of a media constituting the memory medium.

In such a data recording device, with spike effect, it is necessary to ensure perfect contact of all microdots with a sensitive area (recording area) of the memory medium. For reasons of complexity of the system, it is not possible to control the position of each microtip individually. However, micro-tips are manufactured collectively, by techniques derived from those of microelectronics, and there is always a dispersion, due to the manufacture, of the height of the microtips. Although this dispersion is minimal, typically of the order of 100 nm, the longest microtip of a network supports more than the others on the memory medium.

To overcome this difficulty, each microtip is cantilevered by one end of a cantilever, analogous to microtip arrays used in local probe microscopy. The flexibility of the cantilever then makes it possible to absorb the constraint of a support.

The article "" Filling the Memory Access Gap: A Case for On-Chip Magnetic Storage "by Steven W. Schlosser et al., Technical Report CMU-CS-99-174, Carnegie Mellon University School of Computer Science, November 1999 describes the cooperation of a cantilever micro-tip array with a memory carrier connected by elastic fasteners to a frame integral with the microtip-supporting substrate, whereby the sensitive area of the memory medium can be moved in its own right. plane by actuators acting in two perpendicular directions By way of example, the displacement of the memory medium may be of the order of 100 μm in each direction, it is then necessary to align millimeter-sized elements (memory medium and microtip network) with nanometric precision, while controlling the contact forces, which are of the order of a few nanoNewtons.But the flatness and parallelism of the surfaces in rega rd imply tolerances respectively less than 50nm and a microradiant. In the aforementioned article, this is made possible by the use of cantilevers and an expensive dynamic alignment process. Moreover, the elastic fasteners represented in this article, of the complex articulated parallelogram type, require numerous technological steps and are therefore expensive. Such a structure may not be sufficiently robust because of the significant mechanical stresses, which are exerted on the joints. Other solutions have been proposed by the Applicant, based on the use of a memory medium comprising a membrane whose flexibility makes it possible to compensate for dispersions in the height of the microtips. The microtips can then be formed directly, without cantilever, on the same base substrate, in which can also be integrated the addressing circuit and control. This monolithic manufacture of the addressing and control circuit and micro-tips reduces the cost of the device.

Thus, WO-A-2004/032132 discloses a memory medium comprising a flexible membrane carried by a frame forming a plurality of cells, each cell being associated with at least one microtip. To eliminate edge effects, which reduce the occupancy rate, the memory medium can be a double membrane with nested frames.

In the document WO-A-2005/013270, the memory medium comprises a deformable memory layer, for example constituted by a flexible layer of polymer, absorbing the dispersion of height of the micro-tips.

Although this approach is effective in absorbing local micro-tip height dispersions, it does not always make it possible to ensure the contact of all micro-tips with the memory medium, while controlling the contact forces. This type of problem occurs in particular when the front face of the substrate carrying the microtips is partially concave, following its deformation during assembly of the device or due to thermal drifts.

Object of the invention The object of the invention is a data recording device which does not have these drawbacks and, more particularly, a less expensive device which makes it possible to ensure good contact between the microtips and the storage medium.

According to the invention, this object is achieved by a device according to the appended claims, more particularly by the fact that the elastic fixing means consist of a flexible fastening membrane extending the sensitive zone at its periphery and allowing a displacement of the zone. sensitive perpendicular to its plane.

The sensitive area of the memory medium preferably comprises a flexible membrane, extended at its periphery by the flexible attachment membrane.

The invention also relates to a method of manufacturing such a data recording device and more particularly to a manufacturing method in which, the sensitive area of the memory medium comprising a flexible membrane, the flexible membrane and the fixing membrane are formed simultaneously in one piece.

Brief description of the drawings

Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of non-limiting example and represented in the accompanying drawings, in which: Figure 1 schematically illustrates, in top view, a particular embodiment of a memory medium of a device according to the invention.

Figure 2 illustrates a device according to the invention, in section along A-A, with an associated actuator.

FIGS. 3 and 4 illustrate, in section, two alternative embodiments of the device according to FIG. 2.

FIG. 5 illustrates, in plan view, an alternative embodiment of the storage medium according to FIG. 1. FIGS. 6 and 7 schematically illustrate, in section, two variant embodiments of a data recording device according to FIG. in which the micro-tips are formed on a convex surface.

Description of particular embodiments

The data recording device conventionally comprises a memory medium 1 cooperating with a network of microtips 2. As in the aforementioned article, the sensitive zone of the memory medium 1 is elastically fixed on an external frame 3, allowing a moving the sensitive area in its plane.

In FIGS. 1 to 3 and 5, the sensitive zone of the memory medium comprises, as in document WO-A-2004/032132, a flexible membrane 4 delimited by an internal frame 5, forming at least one cell. For the sake of clarity, FIGS. 1 and 2 represent a single cell delimited at its periphery by the internal frame 5. In practice, the number of cells may be arbitrary, each cell preferably having a square, rectangular or hexagonal and the membrane can be a double diaphragm with nested frames. As illustrated in FIGS. 1 to 5, the sensitive zone of the memory support is elastically fixed to the outer frame 3 by a flexible attachment membrane 6 extending the sensitive zone, more particularly the flexible membrane 4, at its periphery. Memory layers 9, covering the flexible membrane 4 and, optionally, also the fixing membrane 6 (FIG. 3) on the front face of the storage medium (intended to come into contact with the microtips), complete the storage medium. . In FIGS. 1 to 3 and 5, the membrane 4 is simply delimited by the internal frame 5 and the microtips 2 can be formed directly on a substrate 8. On the other hand, in FIG. 4, the membrane 4 is covered on the rear face of the memory medium, by a support zone 10. In the latter case, the sensitive zone is semi-rigid, which may require the maintenance of flexible support elements of each of the micro-tips on the substrate 8 , for example in the form of cantilevers 11. To guarantee a minimum spacing between the memory layers 9 constituting the medium and its reading circuit, it may then be desirable to form spacing pads 12 on the substrate 8.

The membranes 4 and 6 may be formed simultaneously in one piece by any suitable method. It is thus possible to deposit, on a silicon wafer constituting the rear face of the storage medium (opposite its front face, a sensitive face intended to come into contact with the microtips), a plastic material, which is spread by centrifugal force. The plastics material used is preferably a polymer and, more particularly, a benzocyclobutene (BCB) based resin, such as CYCLOTENE ™.

After deposition of the plastic material constituting the membranes 4 and 6 and possibly memory layers 9, the outer frame 3 and the inner frame 5 or the support zone 10 can be obtained in a conventional manner (photolithography, dry etching or chemical etching). ). As for example, the frames 3 and 5 can be disengaged, in the silicon wafer, by chemical etching, anisotropic, from the back side of the storage medium, to the layer constituting the membranes 4 and 6. It is possibly possible to reverse the order of these steps (manufacture of membranes, memory layers and manufacture of frames) according to the process constraints related to the materials used.

The memory layers 9 formed on the plastic layer may be of any known type, in particular of the type described in document FR-A-2856184.

As represented in FIGS. 2 to 4, the fastening membrane 6 thus constitutes a kind of outer skin which serves as a support structure for the sensitive area of the memory medium comprising the flexible membrane 4, while allowing it freedom of movement on the vertically, to ensure the plating of the sensitive zone against microtips 2, and horizontally to allow an elastic displacement of the sensitive zone in its own plane, under the action of actuators 7 cooperating with the internal frame 5 or the support zone 10 (only one actuator 7 is shown in FIGS. 2 to 4). The dimensions of the peripheral fixing membrane 6 fix its stiffness. Its thickness is preferably of the order of a few microns and its width of the order of a few millimeters.

The fixing membrane 6 can be lightened to increase its flexibility. It is in particular possible to reduce the surface of this membrane in an etching step, so as to obtain a perforated attachment membrane 6 or in the form of flexible strips, for example curved as in FIG.

5. The etching of the fixing membrane 6 may be carried out by any conventional method and, in particular, by a plasma etching localized by means of a mask or a stencil. In the aforementioned documents, the micro-tips 2 are formed, with or without cantilevers on the front face of a planar substrate. However, deformations of the front face of the substrate are particularly likely to appear during the assembly of the device or due to thermal drifts. Such deformations, making the front face of the concave or saddle-shaped substrate, can lead to a lack of contact between the sensitive area of the memory medium 1 and some of the micro-tips 2.

As shown in FIGS. 2 to 7, this problem is solved by the use of a microtip support substrate 8 having a convex front face 8a. Indeed, the free ends of all the micro-tips 2 then come into contact with the sensitive area of the memory medium 1, the flexibility of which is sufficient to absorb at least a large part of the height variations of the micro-tips. The camber of the front face 8a of the substrate 8 remains small but sufficient to take account of the deformations likely to appear in the opposite direction during assembly of the device or due to thermal drifts. In practice, the radius of curvature of the convex surface can be between 1m and 5m. It is preferably of the order of two meters, which corresponds to a camber of the order of 10 nm over 100 μm.

Such a camber of the front face of the substrate 8 may in particular be obtained by chemical mechanical polishing (CMP) of the front face 8a before formation of the micro-tips. In this case, as illustrated in FIGS. 2 to 4 and 6, the rear face 8b of the substrate 8 remains substantially flat.

The camber of the front face 8a can also be obtained by applying a mechanical stress on the substrate 8. This mechanical stressing can, for example, be achieved by the deposition of a thin layer

(not shown), stress in compression, on the front face 8a or by deposition of a thin layer (not shown), voltage stress, on the rear face 8b. In both cases, the application of such a thin layer mechanically constrained, in compression or in tension, causes a substantially parallel deformation of the front faces 8a and 8b of the substrate 8, as shown in FIG. In particular embodiment, the thin layer is a layer of constrained silicon nitride or silica which is a few hundred nanometers thick, which can withstand without difficulty a stress of 1 GPa.

The strained layer may in particular be obtained by ion beam sputtering (IBS). It may also have been previously constrained by another substrate, said original substrate, and reported on the substrate 8 to arch by any appropriate transfer technique, for example by gluing and thinning of the original substrate. The thickness of the substrate 8 is advantageously chosen to facilitate the cambering step. By way of example, the substrate 8 may have a reduced thickness, of the order of 100 μm, for example.

When the sensitive area of the memory medium is sufficiently flexible, the micro-tips 2 can be formed directly, without cantilever, on the base substrate 8, in which the addressing and control circuit can also be integrated.

As indicated above, the flexibility of the sensitive area of the memory medium 1 comprising the membrane 4 cooperates with the convex surface substrate to ensure contact between the microtips 2 and the sensitive zone and absorb most of the height variations. micro-tips. The combination of a memory medium according to FIGS. 1 to 5 with a substrate 8 whose front face 8a carrying the microtips 2 is convex makes it possible to guarantee a good redistribution of the assembly force between all the micrometers. tips. Indeed, during assembly, the external frame 3 may be secured to the substrate 8, while maintaining the freedom of movement of the sensitive zone in its plane. The outer frame 3 can in particular be fixed to the substrate 8 by conventional methods, such as gluing, thermofusion or any adhesion process between the walls. The assembly force then plates the storage medium, more particularly its sensitive area comprising the flexible membrane 4, on the microtip array 2. The elementary force exerted by each microtip 2 may be of the order of 0.1. nN at 1OnN. It depends on the chosen radius of curvature. By way of example, the assembly force can then be greater than 1 mN.

The data recording device generally comprises means (in particular the actuators 7) allowing a relative displacement of the sensitive area of the storage medium 1 and microtips 2 in the substantially horizontal plane of the sensitive area. It may also comprise displacement means substantially perpendicular to the microtip support substrate 8 (vertically) to bring the microtips in contact with the sensitive zone.

By way of example, the respective dimensions of the various elements represented in FIG. 1 can be as follows: of the order of 15 mm for the side d of the storage medium 1, of the order of 9.5 mm for the c2 side of the membrane 4, of the order of 0.25 mm for the width 11 of the inner frame 5, - of the order of 0.5 mm for the width 12 of the outer frame 3 and of the order of 2 mm for the width 13 of the fixing membrane 6.

Claims

claims A data recording device comprising a two-dimensional array of micro-tips (2), of nanometric dimensions, arranged facing a memory medium (1) and means for elastic fastening of a sensitive area of the memory medium ( 1) on an outer frame (3), allowing a displacement of said sensitive area in its plane, characterized in that the elastic fixing means are constituted by a flexible fixing membrane (6), extending the sensitive area to its periphery and allowing a displacement of the sensitive area perpendicular to its plane. 2.. Device according to claim 1, characterized in that the sensitive area of the storage medium comprises a flexible membrane (4) extended at its periphery by the flexible fixing membrane (6). 3. Device according to claim 2, characterized in that Ia flexible membrane (4) and the fixing membrane (6) are plastic. 4. Device according to claim 3, characterized in that the plastic material is a benzocyclobutene-based resin. 5. Device according to any one of claims 1 to 4, characterized in that the fixing membrane (6) is lightened. 6. Device according to any one of claims 1 to 5, characterized in that the micro-tips (2) are formed directly on a convex front face (8a) of a substrate (8). 7. Device according to claim 6, characterized in that the convex front face (8a) has a radius of curvature of between 1 m and 5m. 8. Device according to one of claims 6 and 7, characterized in that electronic means (5) for addressing and control microdots are integrated in said substrate (8). 9. A method of manufacturing a device according to any one of claims 1 to 8, characterized in that the sensitive area of the memory medium comprising a flexible membrane (4), the flexible membrane (4) and the fixing membrane (6) are formed simultaneously in one piece. 10. Method according to claim 9, characterized in that the flexible membrane (4) and the fixing membrane (6) are formed by spin coating a plastic material on a silicon wafer constituting a rear face of the support of memory (1). 11. The method of claim 10, characterized in that it comprises an etching step to lighten the fixing membrane (6). 12. Method according to one of claims 10 and 11, characterized in that the outer frame (3) and an inner frame (5) defining the flexible membrane are made by etching in said silicon wafer. 13. Method according to one of claims 10 and 11, characterized in that the outer frame (3) and a zone (10) for supporting the flexible membrane are made by etching in said silicon wafer.