WO1996035212A1

WO1996035212A1 - Micromechanically manufactured read/write head for charge coupled devices

Info

Publication number: WO1996035212A1
Application number: PCT/EP1995/001640
Authority: WO
Inventors: Thomas Bayer; Johann Greschner; Helga Weiss
Original assignee: International Business Machines Corporation
Priority date: 1995-04-29
Filing date: 1995-04-29
Publication date: 1996-11-07
Also published as: DE19614072A1; EP0772876A1

Abstract

A micromechanically manufactured read/write head (1) for charge coupled devices has a holder (2), a bearing arm (3) and a point (4) with a shaft (4a) and a front end (4b). The holder (2), the bearing arm (3) and the point form an integrated part (5) made of conductive material. The front end (4b) of the point (4) can directly contact the surface of a charge coupled device to read and write information. The shaft (4a) of the point (4) has a small diameter and is surrounded by a reinforcing sheath (6).

Description

DESCRIPTION

Micromechanically manufactured read / write head for charge storage elements

The present invention relates to a read / write head for charge storage elements, which is manufactured micromechanically, and to a method for its production.

Based on scanning tunneling or scanning force microscopy, a number of new storage methods have been proposed, such as a nitride oxide silicon (NOS) storage element consisting of a silicon substrate and applied thin layers of oxide and nitride. In such a case, charge is written into the thin nitride film using a fine tip. When an electrical pulse is applied between the tip and the silicon substrate, charge will flow through the thin oxide layer into the nitride and be held there. This can be called a write operation. With the same tip, the information can also be read out or deleted. With such storage elements, storage densities of 30 Gbit / in ^{2 were} achieved with charge area units of approximately 150 nm in diameter. The structures available for writing and reading and also used have actually been developed as an inductive magnetic read / write head and are therefore not optimally suited for use with NOS memory elements. Their complex structure hardly allows any further reduction of the active read / write area. Because of the big lateral dimensions of approximately 12 mm × 600 μm, an arrangement with several read / write heads cannot be implemented, but this is desirable in view of an improved data rate due to parallel processing.

A memory element with an arrangement of a plurality of read / write heads is described in US Pat. No. 5,307,311. The storage element consists of several support arms that store bits, and the read / write heads are arranged opposite the support arms. The structure of the read / write heads is very similar to the known tips for scanning tunneling or atomic force microscopy. With this tip shape, the frequent direct contact with the surface of a charge storage element in long-term operation leads to signs of wear at the tip, which leads to a changed contact surface, so that the worn tip, compared to a perfect new tip, has a different force on the surface of a tip Charge storage element presses.

The object of the invention is to provide a micromechanically manufactured read / write head for charge storage elements, the tip of which is designed such that it can come into direct contact with the surface of a charge storage element for writing and reading information and also works reliably in long-term operation.

This object is achieved by the micromechanically manufactured read / write head according to claim 1 and a method for its manufacture according to claim 8. The micromechanically manufactured read / write head for charge storage elements consists of a holding part, a support arm and a tip with shaft and front end. The holding part, support arm and tip are formed as an integrated part made of conductive material. The front end of the tip is formed so that it can come into direct contact with the surface of a charge storage element for writing and reading information. The shaft of the tip has a small diameter and is surrounded by a reinforcing sheath.

The method for producing read / write heads for charge storage elements comprises the following steps:

Providing a silicon substrate, applying a mask layer on the substrate, forming a mask pattern by means of photolithographic processes, producing the shaft of a tip by transferring the mask pattern into the substrate by reactive ion etching, forming a support arm and a holding part from the substrate, thinning the shaft and removing the Mask layer.

The shaft is thinned by thermal oxidation, in which an oxide layer completely enveloping these two parts grows simultaneously on the support arm and the holding part and the mask layer prevents oxidation at the front end of the tip. This ensures that the active surface and thus the contact surface pressure always remain the same when abrasion or abrasion cannot be completely excluded in the operating state. The size of the the charge area unit representing information written in therefore always remains constant.

In the following the invention and particularly advantageous embodiments are described in more detail with reference to the drawings, wherein

1 shows the micromechanically produced read / write head for charge storage elements schematically in cross section;

Figure 2 is a schematic cross-sectional representation of a read / write head with a two-layer reinforcing sheath;

3 shows an arrangement with several read / write heads in top view;

Fig. 4 is a representation of the arrangement with several read / write heads in a schematic cross section and

5A, B and C illustrate the most important process steps for the production of the read / write heads.

The schematic cross-sectional view in Fig. ^"1 illustrates an embodiment of the fabricated by micromechanical methods read / write head according to the invention for charge storage elements. The head 1 is composed of a holding member 2, a bracket 3 and a tip 4 with the shaft 4a and the front end 4b. Holding part 2, support arm 3 and tip 4 have been produced as an integrated part 5 made of conductive material. Highly doped silicon, which can be processed well with the known micromechanical methods, is particularly suitable for this.

The shaft 4a has a very small diameter and is surrounded by a reinforcing sheath 6. The front end 4b of the tip, which is intended to read and read information in direct contact with the charge storage element, must in no case be covered by the reinforcing sheath 6.

Since the tip shaft 4a and the actually active surface of the front tip end 4b are made as thin as possible, the tip would very easily bend or even break off without the reinforcing sheath 6 surrounding the shaft when writing or reading in contact with the charge storage element. In any case, a significant abrasion or abrasion would soon be expected.

The electrically conductive core or tip shank 4a should have no cross-sectional fluctuations over its entire length. Only then is it ensured that, in the event of abrasion or abrasion which cannot be completely excluded, the active surface and thus the contact surface pressure always remain the same. This also ensures that the size of the cargo area unit representing the inscribed information always remains constant. This means that the shaft 4a of the tip 4 should have side flanks which are as vertical as possible. With extremely small shaft diameters of less than 50 nm, at Ultrafine peaks have reached values below 20 nm, and for shaft lengths of approximately 20 μm this corresponds to a ratio of tip length to active tip diameter in the range of approximately 10,000.

It is important for the tip 4 that its geometrical specifications are adhered to exactly, the geometry to be maintained and the manufacturing technology being closely linked.

The most important process steps for the production of the read / write heads are shown in FIGS. 5A, B and C. Many of the required process steps have already been described in detail in European Patent 0 413 040.

A mask layer is applied to a silicon substrate and the mask layer is structured using photolithographic processes to form a mask pattern 9. The mask pattern is then transferred into the substrate to form the shaft 4a of a tip 4. Reactive ion etching is particularly suitable for this process step. The result of this process step can be seen in Fig. 5A. Simultaneously with the formation of the pointed shank or subsequently, the support arm 3 and a holding part 2 are formed from the same substrate.

The shaft 4a is thinned, the thinning in contrast to the thinning step in European Patent 0 413 040, where it is carried out by isotropic wet etching, here by thermal oxidation. This thinning of the shaft 4a by thermal oxidation lets a silicon dioxide layer grow out of and on the previously formed shaft of the tip. As a result of the material conversion from silicon to silicon dioxide taking place, the shaft diameter on the one hand shrinks and on the other hand the thickness of the sheath 6 reinforcing the shaft increases accordingly. The finer the active shaft area, the more stable the surrounding oxide shell becomes. The oxide shell can be up to several µm thick. Since thermal oxidation is one of the most controllable processes in micromechanics and microelectronics, this process step can achieve shaft diameters that are significantly smaller than 50 nm, and even less than approximately 20 nm.

In addition to the mechanical support function for the tip shaft 4a, the thick oxide sheath 6 also takes on the task of slowing down or even preventing material removal of the tip by abrasion or grinding when the surface of charge storage elements contacts.

The contact force is set primarily by the rigidity of the support arm 3. The largest possible contact area therefore means less pressure and thus slower removal, abrasion or sanding. The contact forces are, as in scanning tunneling or atomic force microscopy, around 10 ^-7 to 10 ^{~ 9} N. In scanning tunneling or atomic force microscopy, however, the pressure on the tip is much higher than in the read / write heads described here, whose front tip end is designed so that it can come into direct contact with the surfaces of charge storage. A short calculation example should prove this. The pressing force is 10 ^"8 N and the tip cross-section (10 x 10) nm. This leads to a surface pressure of 10 ² N / mm ^2. The read / write head described here has a cross-sectional area of 3 x 3 μm. This leads to a Surface pressure of about 10 ^"3 N / mm ² . The surface pressure is thus 10 ⁵ times lower than with the tips for scanning tunneling or atomic force microscopy.

In the case of thermal oxidation, an oxide layer 6 completely enveloping these two parts also grows out of / on the support arm 3 and the holding part 2, as shown in FIG. 5B.

During this oxidation step, in which an oxide shell is formed with a possibly greater thickness than the mask layer itself, the mask layer 9 has to ensure that no oxidation takes place at the front end 4b of the tip 4 and is removed after the oxidation, FIG. 5C. It is therefore necessary to choose a very dense material that is impenetrable to oxygen molecules for the mask layer. Silicon nitride is particularly suitable.

As shown in FIG. 2, the reinforcing sheath 6 can not only consist of an oxide layer, but can also be constructed from a plurality of dielectric layers 6a, 6b. Such a second or further covering layer prevents the tip from being abraded and worn even more reliably. Diamond-like carbon, which is the best of the known materials to be applied as a thin layer, is best suited for these second or further layers has abrasion-preventing properties. Likewise, the oxide layer or the plurality of dielectric layers can also be covered by a conductive layer, which is used, for example, for grounding purposes and allows improved electrical signal routing.

As can be seen in FIG. 1 or 2, the mechanical holding part 2 has regions 7 which are not covered by the reinforcing sheath 6. These areas are used for electrical contacting of the read / write head and, if necessary, hybrid or monolithic control and evaluation electronics 8 can be applied in these areas. For this purpose, it is necessary to create contact openings in the dielectric or conductive layer 6b and in the thermal oxide layer 6a in the provided areas 7 of the holding part 2 to the silicon substrate.

An important factor for usable storage concepts is not only the storage density, but also the data rate when writing and reading. Today's magnetic data storage devices have data rates of a few MBytes / sec. Such data rates can only be achieved with the read / write heads presented here through the targeted simultaneous use of a large number of heads working in parallel.

Since the read / write heads described here are manufactured micromechanically, arrangements with a plurality of read / write heads 10 can also be produced in a simple manner, for example as shown in FIG. 3. Fig. 4 shows a representation of the arrangement with several read / write heads in a schematic cross section.

Support arm 3 and tip 4 of an individual read / write head 10 are each formed as an integrated part 50 made of conductive material and insulated from the common holding part 20. The electrodes representing the individual read / write heads are insulated from the substrate, which can be achieved by means of a silicon-on-insulator (SOI) substrate in which two single-crystal silicon wafers are separated from one another by a thermal oxide.

Single heads as well as arrangements with several read / write heads can be manufactured extremely cheaply by batch fabrication.

Claims

PATENT CLAIMS

1. Micromechanically manufactured read / write head (1) for charge storage elements consisting of

a holding part (2),

a support arm (3) and

a tip (4) with shaft (4a) and front end (4b),

in which

Holding part (2), support arm (3) and tip (4) are formed as an integrated part (5) made of conductive material;

the front end (4b) of the tip (4) is designed such that it can come into direct contact with the surface of a charge storage element for writing and reading information; and

the shaft (4a) of the tip (4) has a small diameter and is surrounded by a reinforcing sheath (6).

2. Read / write head according to claim 1, wherein the shaft (4a) of the tip (4) has vertical side flanks and the ratio of tip length to tip diameter is in the range of approximately 10,000.

3. read / write head according to claim 1 or 2, wherein the holding part (2) and the support arm (3) are also surrounded by the reinforcing shell (6).

4. read / write head according to one of claims 1 to 3, wherein the reinforcing sheath (6) from one or more dielectric layers (6a, 6b) or from one or more dielectric layers and an overlying conductive layer is constructed.

5. read / write head according to claim 3 or 4, wherein the holding part (2) has areas (7) which are not covered by the reinforcing sheath (6) and to which hybrid or monolithic control and evaluation electronics (8) is applied.

6. read / write head according to claim 4 or 5, wherein the integrated part (5) consists of highly doped silicon and the dielectric layers of the reinforcing sheath (6) consist of silicon dioxide and diamond-like carbon.

7. An arrangement with a plurality of read / write heads (10) according to one of the preceding claims 1 to 6, wherein the support arm (3) and tip (4) of a single read / write head (10) each as an integrated part (50) made of conductive material formed and isolated from the common holding part (20).

8. A method for producing read / write heads for charge storage elements according to one of claims 1 to 6, comprising the following steps:

Providing a silicon substrate

Application of a mask layer on the substrate

Forming a mask pattern (9) by means of photolithographic processes

Production of a shaft (4a) of a tip (4) by transferring the mask pattern (9) into the substrate by reactive ion etching

Forming a support arm (3) and a holding part (2) from the substrate

Thinning the shaft (4a)

Removing the mask layer (9)

characterized in that the thinning of the shaft (4a) takes place by thermal oxidation, in which an oxide layer (6) completely enveloping these two parts grows on the support arm (3) and the holding part (2) and the mask layer (9) oxidizes front end (4b) of the tip (4) prevented.

9. The method according to claim 8, characterized in that the mask layer (9) consists of silicon nitride.

10. The method according to claim 8 or 9, characterized in that a further dielectric layer (6b) or a conductive layer (6b) is applied to the thermal oxide layer (6a).

11. The method according to claim 10, characterized in that in certain areas (7) of the holding part (2) to the silicon substrate through contact openings in the dielectric or conductive layer (6b) and in the thermal oxide layer (6a) are created.