WO1999026264A1

WO1999026264A1 - Microrelay

Info

Publication number: WO1999026264A1
Application number: PCT/DE1998/003407
Authority: WO
Inventors: Ralf Schnupp
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1997-11-14
Filing date: 1998-11-13
Publication date: 1999-05-27
Also published as: EP1031161B1; ATE213565T1; DE19750559C1; EP1031161A1; DE59803149D1

Abstract

A microrelay manufactured by microsystem technology and a process for manufacturing the same are disclosed. In the claimed microrelay, the excitation coil has a conical form. This conical arrangement of the coil windings induces a magnetic field which is substantially more homogeneous than in planar coils. Due to this more homogeneous magnetic field, the relay contact elements are pressed more strongly onto the contact surfaces and an electromagnetic relay with higher wear resistance and longer service life is obtained. The conical arrangement of the coil windings can be obtained by metal deposition and structuring on the walls of a pit anisotropically etched in a silicon chip.

Description

Micro relay

description

The present invention relates to a microsystem-manufactured micro relay and a method for its production. Particularly in the areas of telecommunications, medical technology, data processing, measurement technology and in the automotive sector, there is a great need for miniaturized relays.

So far, mainly electrostatic relays have been used for a variety of applications. However, these relays require high voltages (typically in the range of 100 V), so that specially designed control devices and isolation measures are necessary for operation. However, this increases the system costs.

In H. Hosaka, et al. , Sensors and Actuators A, 40 (1994), pp. 41-47 therefore discuss the advantages of electromagnetic microrelays. The presented there

Microrelay consists of one or more conventional small electromagnets, over which a flat contact spring is moved. Hosaka examined in particular the influence of the contact force on the contact resistance, the dependence of the size of the

Breakdown voltage of the width of the electrode gap and the behavior of different

Contact spring geometries. The Hosaka microrelay enables high switching speeds (around 1 kHz) to be achieved. However, this microrelay cannot be manufactured using semiconductor technology. Micro-relays manufactured using microsystems technology are also known. These consist of a planar coil for generating the magnetic field and separate contact arms of the working circuit, which were generated by suitable etching techniques.

However, the use of planar coils has a number of disadvantages. Planar coils are very susceptible to magnetic fields (see e.g. H. Meinke et al., Taschenbuch der Hochfrequenztechnik, Springer-Verlag Berlin (1968), p. 19). The magnetic field generated with planar coils is also very inhomogeneous and the maximum field strength density is limited. The latter is due in particular to the small line cross section

(with the consequence of a low current flow), which results from the necessary limitation of the large area requirement of planar coils.

For these reasons, the force acting on the contact arms (spring contacts) is relatively small, so that the contact pressure of the spring contacts on the contact surfaces, for example in the event of vibrations, is not sufficient. This results in wear of the contact points and the life of the component is shortened. Furthermore, the maximum adjustable distance of the contact arms and thus also the maximum switchable voltage in the working circuit are limited.

In Y. Watanabe et al. , Sensors and Actuators A 54 (1996), pp. 733-738, describes a manufacturing process for a planar coil that works with higher current densities and can therefore generate higher field strengths. However, this coil also has the above problems due to the inhomogeneity of the magnetic field. The object of the present invention is to provide a microrelay and a method for producing the same, which has a longer service life and less wear than known microrelays with a planar coil, and is simple to produce by means of semiconductor technology.

This object is achieved with the features of the applicable claims 1 and 13, respectively. Advantageous developments of the invention are the subject of the dependent claims.

The microrelay according to the invention, like the known microrelays, consists of an excitation coil for generating a magnetic field and one or more contact elements. The contact elements can be, for example, free-standing contact arms or contact springs clamped on one side. Elastic contact bridges clamped on two sides or comparable contact elements clamped on several sides are also suitable. These contact elements are made by

Action of the magnetic field of the coil pressed against a contact surface or detached therefrom, so that thereby a contact in a working circuit is closed or opened. According to the invention, the microrelay has a coil with a conical shape.

This conical arrangement of the coil turns induces a much more homogeneous magnetic field than in the case of planar coils. Due to this more homogeneous magnetic field, a higher contact pressure of the contact elements on the contact surfaces is generated, so that a higher wear resistance and longer life of the electromagnetic relay can be achieved. Switching times are also shortened. A larger conductor cross section of the excitation coils, which due to the smaller area requirement of the conical coil can be generated allows the use of higher currents and thus the generation of stronger magnetic fields. This makes it possible to maintain larger distances between the contact arms, so that the switchable voltage in the working circuit can be increased.

A further increase in the field strength can be achieved in a simple manner by filling the interior of the conical coil with ferromagnetic material. Filling the interior completely is an advantage.

Another advantage of the microrelay according to the invention is that it can be easily integrated into one

Semiconductor substrate, as is the case with the invention

Procedure is carried out. The method also has the advantage that all components of the microrelay can be produced together on one semiconductor wafer in one process run. The semiconductor compatibility of the microrelay is particularly advantageous.

In a special embodiment, the electromagnetic microrelay is composed of two parts produced by microsystem technology, a component with the excitation coil and a component with contact elements.

The component with the excitation coil consists of a trench etched anisotropically in a silicon wafer, the bottom surface of which is electrically connected to the opposite side of the wafer (hereinafter referred to as the front side) via a highly doped diffusion region. On an insulation layer on the

A metal layer is deposited on the trench walls. By The intended coil structure is produced by lithography of a galvanic photoresist applied thereon. In the same process step, the contact surfaces and the lead-out of a coil connection are formed on the rear of the pane. The second coil connection is led through the via (the highly doped diffusion region) to the front of the disk.

Then in this embodiment, the

Conductor cross sections increased by galvanic metallization. Finally, after an insulation layer has been deposited, the interior of the coil is filled with a ferromagnetic material.

The contact elements are also produced by anisotropically etching a trench in a silicon substrate using the etching stop on highly doped layers. In this way, free-standing cantilevers or tongues (as contact arms) are formed, onto which a ferromagnetic and the contact metal have been previously deposited and structured. By applying a system of layers braced against one another, the bend and thus the distance between the tongues and the contact surfaces on the coil unit can also be adjusted. These are layers with different coefficients of thermal expansion. In the last manufacturing step, the two components are placed on top of each other, whereby different bonding techniques can be used. Furthermore, the connections to the housing are made.

A preferred production method for a micro relay according to the invention is described below with reference to the drawings. Here show: Fig. 1 shows an example of the design of the

Coil unit of the microrelay according to the invention;

Fig. 2 shows an example of the unit with the

Contact elements of the microrelay according to the invention;

3 to 11 different manufacturing steps of the units of the invention

Micro relay according to Figures 1 and 2. and

12 and 13 a further embodiment of the

Coil unit and the unit with the contact elements of an inventive

Micro relay.

Fig. 1 shows a coil unit of a microrelay according to the invention with contacts for a two-pole relay. In the following, the side of the coil unit visible in FIG. 1 is referred to as the rear side. The coil unit is formed from a silicon substrate 4 which has an anisotropically etched trench 6. The coil turns of the excitation coil 1 are located on the trench walls. One coil end is connected in an electrically conductive manner to the coil contact 10 on the front side of the substrate 4 via the highly doped silicon region 7 at the bottom of the trench 6. The coil contact 10 is separated from the silicon substrate 4 by an insulation layer 13 (Si0 ₂ ). Likewise, the coil turns of the coil 1 and the further connection surfaces on the back of the substrate are insulated from it by a layer 22. The input poles 3a and the output poles 3b forming the contact surfaces are also arranged on the back of the substrate 4. By connecting the input to the output poles via the contact springs Component (Fig. 2), a working circuit is closed. Furthermore, the coil contact 11 and solder contacts 9 are located on the back of the substrate.

FIG. 2 shows a unit with spring contacts 2 which, together with the coil unit from FIG. 1, form a microrelay according to the invention. The visible surface of this unit is referred to below as the front. The unit with the spring contacts consists of a silicon substrate 5 with an anisotropically etched trench 8, through which the spring contacts are exposed. On the front of the substrate 5 there are solder contacts 9 within an Si0 ₂ / Si ₃ N ₄ layer 13, 14. The spring contacts 2 themselves consist of a layer sequence of highly doped n ⁺⁺ silicon, Si0 ₂ / Si ₃ N ₄ , chromium , Nickel and gold.

A preferred manufacturing process for the relay according to FIGS. 1 and 2 will now be described with reference to FIGS. 3 to 11. When the individual process steps are shown, the cleaning steps customary in semiconductor technology are not listed, although they are of course carried out. The front side of the silicon substrates corresponds to the top side in the following figures. to

To simplify matters, the coil unit with the coil component and the unit with the spring contacts with the spring contact component are named.

Low-resistance, p-doped silicon wafers are used as the starting material for the manufacture of the micro relay. Typical slice thicknesses are between 300 μm and 700 μm. Disc diameters of 100 mm or 150 mm are currently customary, on which a large number of micro-relays according to the invention can be produced. The microrelay consists of two micromechanically made parts made of silicon (coil component and spring contact component), which at the end of the

Manufacturing process are put on top of each other. Unless otherwise described, the following manufacturing steps relate to both sub-elements. Different process steps are identified by separate figures.

A scatter oxide 13 is first thermally grown on the silicon wafer 4, 5 for the subsequent implantation step (see FIG. 3). The typical thickness of the scatter oxide layer 13 here is in the range of 20 nm. The oxide grows on both sides of the pane.

An approximately 500 to 1500 nm thick photoresist layer 15 is then applied and photolithographically removed at the locations to be implanted (cf. FIG. 3). The dimensioning and arrangement of these

Areas are selected in the case of the excitation coil so that the implanted area forms the bottom of the trench 6 which is subsequently etched (cf. FIG. 1). It represents the through contact to the front of the substrate 4. In the case of the spring contact component, the area to be implanted corresponds to the shape and area of the spring contacts (cf. FIG. 2).

High dose ion implantation follows to produce highly doped n regions 7, 16. Typical elements for n ⁺⁺ implantation are phosphorus and arsenic.

The scatter oxide 13 is then removed by wet chemistry at the exposed locations on the front side and on the entire rear side. The lacquer layer 15 is then removed. After a thermal diffusion step at temperatures around 1000 ° C., a relatively homogeneously distributed n "layer 7, 16 forms in the p-doped silicon substrate 4, 5 (see FIG. 4). This highly doped region is necessary for the electrochemical etching stop during the following anisotropic etching step, and as an electrical contact area 7 for the excitation coil 7. Furthermore, these highly doped areas are not attacked by the anisotropic etching solution, so that free-standing cantilevers or tongues 2 are formed for the spring contacts μm.

In order to protect the front of the pane from scratching during the subsequent nitride deposition and in the dry etching process, it is provided with a coating 17 over the entire surface (see FIG. 4). Silicon nitride 18 is deposited on the back of the substrate 4, 5 as a mask for the anisotropic etching by means of cathode sputtering (see FIG. 4).

This is followed by lacquering 19 of the rear side and the photolithographic exposure of the region to be etched anisotropically (cf. FIG. 4).

By dry etching in the plasma

Silicon nitride layer 18 removed at the free locations on the back. This defines the later etchable area of the silicon substrate. The areas to be etched are selected so that the disk component cannot be completely etched through in the coil component, ie the etching process stops at the highly doped n-region 7 (see FIGS. 5A and 1). The exposed area of the spring contact component, on the other hand, extends beyond the n-regions 16 in such a way that the etching solution penetrates to the front of the pane and free-standing arms are formed (see FIGS. 5B and 2). Then the lacquer 17, 19 is peeled off on both sides.

A combination of silicon oxide and silicon nitride is deposited on the spring contact component in order to produce spring contacts bent downwards. 5B shows this layer 14. Silicon oxide has a lower coefficient of thermal expansion than silicon, silicon nitride a higher one. When the discs cool down after the deposition processes, tensile or compressive stress acts on the contact arms depending on the thickness of the two layers. As soon as the contact arms are free, they consequently bend upwards or downwards (cf. FIG. 2). In this way, the production of relays is possible, the working circuit of which is open or closed in the idle state. This process step is omitted for the coil component.

To determine the conductor tracks and contact areas of both components using the layer lift-off process, the front is now lacquered and photolithographically structured. Here, a negative varnish 20 with thicknesses between 2 and 5 μm should be selected.

Next, a thin (20 to 50 nm is sufficient) chrome layer for adhesion and a 1 to 3 μm thick nickel layer as the basis for the galvanic gold plating of the conductor tracks.

This layer combination 21 can be seen in FIGS. 5A and 5B. Nickel is ferromagnetic and therefore also serves as a magnet for attracting or repelling the spring contact arms. The thicker the layer, the better the switching behavior of the relay.

When the lacquer is removed, the metals deposited on the lacquered areas are also removed, so that the desired conductor pattern is formed on the front side (see FIGS. 6A, 6B and 2). To increase the Mechanical stability of the microrelay, small solder contact surfaces 9 are attached to several points of the spring contact component (cf. FIG. 2).

The spring contacts and the conical coil space are now exposed by means of anisotropic etching in an alkaline solution (e.g. potassium hydroxide). The front of the pane must be protected from the solution by a suitable holder. Due to different removal rates of potassium hydroxide in different crystal directions of the silicon, the side walls are always inclined by 54.74 ° with respect to the surface of the pane (see FIGS. 6A, 6B, 1 and 2; not shown in the correct angle). In both components there are different effects for the automatic

Stop of the etching process exploited. In the coil component, the etching process is brought to a standstill about 5 μm before reaching the n-region 7 by applying a suitable voltage to the highly doped via 7 of the excitation coil (electrochemical etching stop, see FIG. 6A). In the spring contact component, use is made of the fact that potassium hydroxide attacks highly doped regions, oxides and nitrides only very slightly, so that the structure of the component shown in FIG. 6B is produced.

The rear silicon nitride 18 is then removed by dry etching on both components. Furthermore, the exposed combination layer of oxide 13 and nitride 14 is etched on the spring contact component, so that free-standing spring contacts clamped on one side are produced (see FIG. 7). With the exception of the galvanic gold plating of the metal areas, this component has now been completed and will therefore not be included in the next steps. The coil component is then coated on the front (not shown in the figures) in order to protect the surface from the subsequent processes.

In an isotropic etching step (e.g. in a dilute

Hydrofluoric acid) the edges formed during the anisotropic etching are rounded with an overhang of about 3 to 5 μm (cf. FIGS. 6A, 6B and 7). The result can be seen in FIG. 8.

A low-temperature oxide 22 is deposited on the etched rear side (e.g. with sputtering), which serves as an electrical insulator to the silicon substrate. Subsequently, a thin, preferably reflection-free metal layer 23 (for example titanium with a layer thickness of 50 nm) is deposited on the back (see FIG. 8).

Electrochemical varnish 24 with a thickness of 5 to 25 μm is deposited on this metal layer (for example electroplating varnish PEPR 2400, Shipley) and structured photolithographically so that the area above the via 7 is exposed (see FIG. 8). Then the titanium layer 23 and the oxide layer 22 are removed there by wet chemistry (see FIG. 9). In the next step, the galvanic lacquer 24 is removed.

This is followed by the deposition of a titanium layer with a thickness of some 100 nm, which is coated with a wafer-thin nickel layer of a few nanometers in thickness. This layer combination 25 is shown in FIG. 9. It serves as the basis for the subsequent galvanic gold plating.

Electrochemical lacquer 26 with a thickness of 5 to 25 μm is deposited on this layer (electroplated lacquer PEPR 2400) and structured photolithographically, so that the Coil geometry and the conductor tracks of the

Rear of the pane can be defined (see FIGS. 9 and 1). The solder contacts 9 provided on the spring contact component to increase the mechanical stability of the microrelay can also be found mirror-inverted (see FIG. 1).

Now the titanium / nickel layer 25 is removed wet-chemically at the open positions. The titanium / titanium / nickel layer is shown in Figure 10 as a layer. The electroplating lacquer 26 is removed.

To increase the conductor cross-sections (thicknesses from 1 to 20 μm), the metal areas on both components are now electroplated (see Fig. 10, layer 27). The components produced on the semiconductor wafer are then separated by sawing.

At the end of the manufacturing process, the two components are connected using a reflow soldering process. For this purpose, a fusible solder 28 is applied to the points to be joined and the second component is attached. A firm, conductive connection is achieved by tempering the parts. 11 shows the assembled components which form the microrelay according to the invention.

To increase the magnetic field and the associated benefits, i.e. Shortening the switching times, increasing the switchable voltages and currents,

Vibration resistance, lower contact resistance and consequently lower contact load, etc., the installation of a ferrite core in the coil space is possible. For this purpose, an insulation layer is applied to the coil tracks (for example lacquers with high viscosity or oxide). Then one ferromagnetic layer, a ferrite mass or a ferrite core introduced. Alloys of iron and nickel have proven themselves as materials.

1 and 2 show a two-pole relay, which has open contacts in the idle state. However, the above method can also be used to produce one or more poles relays which can have a contact which is open in the idle state or a contact which is closed in the idle state.

Furthermore, the use of bimetals on the spring contact arms is advantageous, since this allows the production of bimetallic relays, the states of which can be changed by short current pulses.

In the above description of the manufacture of a microrelay according to the invention, the spring contact component is placed with its front on the rear of the coil component. With a suitable arrangement of the conductor tracks, contact surfaces and solder contacts, however, it is also possible to connect both components on the front. Furthermore, of course, a different construction of the two components is permitted, as is the case, for example, in FIGS

12 and 13 is shown. Here, for example, the contact arms 2 are arranged on the rear side of the spring contact component, the trench, as with the coil component, only reaching up to a highly doped region 16 as the bottom of the trench. Also in this example are the

Input poles 3a and 3b output poles arranged on different components.

Because of the possibility of switching high voltages and with correspondingly large conductor cross-sections also high currents, the microrelay according to the invention is for the Particularly suitable for use in the field of power electronics. Characteristic of the relay are the small size and the low power requirement of the electromagnet as well as an ideal conductor path separation.

Due to the high vibration resistance, it can be used in the field of automotive electronics.

Claims

claims

1. Microrelay consisting of an excitation coil (1) for generating a magnetic field, and one or more contact elements (2) which open or close a contact (3) by the action of the magnetic field of the coil, characterized in that the coil (1 ) has a conical shape.

2. Microrelay according to claim 1, characterized in that the coil is integrated in a semiconductor substrate (4).

3. Microrelay according to claim 1 or 2, characterized in that the interior enclosed by the coil is filled with a ferromagnetic material.

4. Microrelay according to claim 1 or 2, characterized in that a ferrite core is arranged in the interior enclosed by the coil.

5. Microrelay according to one of claims 1 to 4, characterized in that the / the contact elements are designed in the form of free-standing contact arms.

6. Microrelay according to one of claims 1 to 5, characterized in that the / the contact elements are designed in the form of spring contacts.

7. Microrelay according to one of claims 1 to 6, characterized in that the relay is composed of two micromechanically manufactured parts, a coil unit (4) and a unit (5) with one or more contact elements.

8. Microrelay according to claim 7, characterized in that the coil unit consists of a silicon substrate (4) with a trench (6) anisotropically etched therein, on the side walls of which the coil windings are located.

9. Microrelay according to claim 8, characterized in that the bottom surface of the trench connects one end of the coil via a highly doped diffusion region (7) with the opposite side of the substrate in an electrically conductive manner.

10. Microrelay according to one of claims 7 to 9, characterized in that the unit with the contact elements consists of a silicon substrate (5) with a trench etched therein (8), above which, starting from an edge of the trench, one or more freestanding Tongues are arranged as contact elements.

11. Microrelay according to one of claims 1 to 10, characterized in that the / the contact elements are constructed from mutually braced layers.

12. Micro relay according to one of claims 1 to 10, characterized in that the / the contact elements have a bimetal layer.

13. A method for producing a microrelay according to one of the preceding claims, comprising the following method steps:

- Anisotropic etching of a trench (6) in a first silicon substrate (4) on a rear side of the substrate;

- depositing an insulation layer (22) in the trench;

- depositing a layer (23, 25) of a coil material on the insulation layer;

- depositing a galvanic photoresist (26) on the layer of the coil material;

- Photolithographic structuring of the photoresist in accordance with a coil structure to be produced on the side walls of the trench;

- removing the coil material (23, 25) from the exposed areas;

- Removing the photoresist (26);

- Manufacture of contact surfaces (3a, 3b) and connection surfaces (10, 11) for the coil turns on the front and back of the first substrate (4);

- Providing a second silicon substrate (5) with one or more contact elements (2) coated with an electrically conductive material;

- Connecting the two substrates so that the contact elements of the second substrate (5) open or close corresponding contacts to contact surfaces (3b) in the other substrate (4) when moving due to the magnetic field of the coil.

14. A method for producing a micro relay according to claim 13, characterized in that before the etching of the trench (6) in the first substrate on the front of the substrate (4) by ion implantation, a highly doped diffusion region (7) is generated, which is the bottom surface of the trench (6) forms and establishes the electrical connection of a coil end to the front of the substrate.

15. A method for producing a microrelay according to claim 13 or 14, characterized in that the contact elements (2) of the second silicon substrate (5) are produced by the following method steps:

- Generating a highly doped diffusion region (16), which has the lateral dimensions of the contact elements (2), on a free-standing contact arm front side of the second substrate (5) by ion implantation;

- depositing an electrically conductive layer (21) in this area;

- Anisotropic etching of a passage (8) or a trench in the second silicon substrate thereof Rear side, so that free-standing cantilevers are exposed as contact elements.

16. A method for producing a microrelay according to one of claims 13 to 15, characterized in that a system of braced layers (14) is applied to the contact elements before the etching step, by means of which a desired later bending of the contact elements is determined.

17. A method for producing a microrelay according to one of claims 13 to 16, characterized in that the cross sections of the coil turns are increased by galvanic metallization (27).

18. A method for producing a microrelay according to one of claims 13 to 17, characterized in that the coil turns are covered with an insulation layer and the trench of the first substrate is filled with ferromagnetic material;

19. A method for producing a microrelay according to one of claims 13 to 18, characterized in that the first (4) and second substrate (5) are present on a common semiconductor wafer and are processed simultaneously.