GB2247953A

GB2247953A - Pressure sensor

Info

Publication number: GB2247953A
Application number: GB9117531A
Authority: GB
Inventors: Jiri Marek; Dieter Seipler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-09-07
Filing date: 1991-08-14
Publication date: 1992-03-18
Also published as: DE4028402A1; GB9117531D0; JPH04245484A

Abstract

A pressure sensor has a silicon sensor element 10 on the two main surfaces of which covers 21, 22 are applied. The silicon sensor element has at least one thin, bendable diaphragm 11, the first surface of which is adjoined by a reference cavity 26 in which a reference pressure prevails, and the second surface of which is adjoined by a measuring cavity 15 so that the pressure to be measured acts on the second surface of the at least one diaphragm. The pressure food into the measuring cavity is formed laterally between one of the two covers and the silicon sensor element, by a trench 13 etched in the sensor element 10, or by a groove 23 in the cover 22. The covers may be of silicon or glass and may be planar or recessed. <IMAGE>

Description

Pressure sensor

Prior art

The invention proceeds from a pressure sensor according to the preamble of the main claim.

Various pressure sensors are already known which have a silicon sensor element from which a thin, bendable diaphragm is constructed. A cavity in which a reference pressure prevails is located between the diaphragm and a cover applied above or below the silicon sensor element. The measuring medium is brought up to the diaphragm from below or above. it is thus possible to distinguish two types of absolute pressure sensors. In one type, the measuring medium is brought up to the side of the membrane on which electronic circuit elements for signal acquisition are integrated. In this variant, a passivation layer is necessary on the top side of the membrane exposed to the measuring medium,, in order to prevent drifting of the electronic circuit elements. The application of passivation layers frequently leads to a mechanical distortion of the diaphragm, so that onchip tuning of the electronic circuit elements before the application of the passivation layer is problematical. In pressure sensors of the second type, the measuring medium is brought up to the rear, that is to say to the side of the membrane on which no electronic circuit elements are integrated. This takes place through an opening in the lower cover of the silicon sensor element. This structure requires an aligned installation of the silicon sensor element with respect to the lower cover.

is Advantages of the invention The sensor according to the invention with the characterising features of the main claim has the advantage that the installation of the sensor is simplified owing to the formation of a lateral pressure feed. An aligned installation on the carrier substrate is not required. Passivation of the surface of the silicon sensor element, in which electronic components are integrated, is not necessary, so that on-chip tuning is unproblematical, and complete integration of the evaluation circuit on the silicon sensor element is also possible. Furthermore, the pressure sensor according to the invention can be realised using materials and processes that are known from microelectronics and microengineering and are very effective in application.

Advantageous developments of the sensor specified in the main claim are possible using the measures set out in the subclaims.

Drawing Exemplary embodiments of the invention are explained in more detail in the following description and represented in the drawing, wherein Figures la, b and 2a, b show various embodiments of the sensor according to the invention, and Figure 3 shows the top view of a silicon sensor element in accordance with Figures la and 2a.

Description of the invention

Various embodiments of the pressure sensor according to the invention are represented in Figures la, b and 2a, b. Common to all the embodiments is the threelayer structure, an upper cover 21 and a lower cover 22 being applied to a silicon sensor element 10. The silicon sensor element 10 has a thin, bendable diaphragm 11. The covers 21 and 22 can consist either of structured or unstructured glass carriers or silicon carriers. Although not represented here, parts of the evaluation circuit can be integrated in the surface of the silicon sensor element. In the silicon sensor elements 10 represented in Figures la, b, the diaphragm 11 has been produced by onesided etching inwards starting from the rear of the silicon sensor element 10. The diaphragm 11 is thus formed inside the front of the silicon sensor element 10. In order to ensure the bendability of the diaphragm 11, a recess which forms a cavity 26 after application to the silicon sensor element 10 is produced in the upper cover 21 in the region of the diaphragm 11. In the embodiments represented in Figures la and b, the cavity 26 is completely closed; a defined reference pressure prevails in it. After application of the lower cover 22, the recess produced by etching inwards from the rear of the silicon sensor element 10 forms a further cavity 15, which serves as measuring cavity in the embodiments represented in Figures la and b. The pressure feed takes place laterally either through an etched trench 13, which is formed in the silicon sensor element 10 and discharges from the outside of the sensor into the measuring cavity 15, as represented in Figure la, or through a groove-shaped recess 23 in the lower cover 22 which reaches from the outside of the sensor into the region of the measuring cavity 15. This is represented in Figure 1b.

The sensor elements 10 represented in Figures 2a and b likewise have a diaphragm 11, which is produced, however, by two-sided etching inwards starting from the front and from the rear of the silicon sensor element 10. The recesses thus produced in the silicon sensor element 10 form cavities 15 and 16 together with the upper cover 21 and the lower cover 22. In this arrangement, the covers 21 and 22 can be unstructured, as in Figure 2a, or else structured, as in Figure 2b. Represented by way of example here is a sensor element 10 which is symmetrically formed with regard to its front and its rear. The closed cavity 16 serves as reference cavity; the cavity 15 serves as measuring cavity and consequently has a pressure feed. This can be realised either by an etched trench 13, as represented in Figure 2a, the etched trench 13 being formed in the silicon sensor element 10 and discharging from the outside of the sensor into tne cavity 15. Another possibility for realising the pressure feed is represented by a groove-shaped recess 23 in the lower cover 22 which reaches from the outside of the sensor into the region of the measuring cavity 15, or else discharges into a recess in the lower cover 22, which is produced in the region of the diaphragm 11.

Represented in Figure 3 is the top view of the rear of a silicon sensor element 10 constructed from a (100)-silicon carrier by anisotropic etching. The diaphragm 11 is produced by etching inwards into the rear of the silicon carrier. In this process,, (111)-planes have been formed as oblique sidewalls of the rear etching in accordance with the crystal orientation of the silicon carrier. At the same time, an etched trench 13, which likewise has oblique (111)-sidewalls, was produced for the pressure feed. This embodiment has the advantage that no aligned installation of a cover is required to produce the measuring cavity, since the silicon sensor element 10 already contains the pressure feed in the form of the etched trench 13.

The scope of the invention also embraces sensor elements produced from silicon carriers having a different crystal orientation or crystal structure. The etched trench is then realised analogously in another crystal orientation.

is

Claims

1. Pressure sensor having a silicon sensor element and having covers applied to the two main surf aces of the silicon sensor element, the silicon sensor element having at least one thin, bendable diaphragm, the first surface of which is adjoined by a reference cavity in which a reference pressure prevails, and on the second surface of which the pressure to be measured acts, characterised in that the second surface of the at least one diaphragm (11) is adjoined by a measuring cavity (15, 26) having at least one lateral pressure feed (13, 23), which are formed between one of the two covers (21. 22) and the silicon sensor element (10).

2. Pressure sensor according to Claim 1, characterised in that the at least one diaphragm (11) is produced in the silicon sensor element (10) by etching a first recess inwards into one surface of the silicon sensor element, which forms a first cavity (15), and by etching a second recess inwards into the other surface of the silicon sensor element, which forms a second cavity (16).

3. Pressure sensor according to Claim 1.. characterised in that the at least one diaphragm (11) is produced by one-sidedly etching a first recess, which forms a first cavity (15), inwards in the silicon sensor element (10), and in that the first cover (21), which is applied to the surface of the silicon sensor element (10), in which the at least one diaphragm (11) is formed, has a second recess, which forms a second cavity (26), in the region of the at least one diaphragm (11).

is

4. Pressure sensor according to Claim 2 or 3, characterised in that the first cavity (15) forms the measuring cavity and the second cavity (16, 26) forms the reference cavity.

5. Pressure sensor according to Claim 4, characterised in that the lateral pressure feed is formed by at least one etched trench (13) in the surface of the silicon sensor element (10). which trench discharges from the outside of the sensor into the first recess.

6. Pressure sensor according to Claim 4, characterised in that the lateral pressure feed is formed by at least one groove-like recess (23) in the surface of the second cover (22) facing the sensor element (10), which recess reaches from the outside of the sensor into the region of the measuring cavity (15).

7. Pressure sensor according to one of the preceding claims, characterised in that the covers (21, 22) are structured or unstructured glass carriers or silicon carriers.

8. Pressure sensor according to one of the preceding claims,, characterised in that electronic circuit elements are arranged on or in a surface of the diaphragm (11) as parts of an evaluation circuit.

9. Any of the pressure sensors substantially as herein described with reference to the accompanying drawings.

Published 1992 atTbe Patent Office, Concept House, Cardiff Road. Newport, Gwent NP9 111H. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwnifelinfach, Cross Keys, Newport, NP1 7HZ. Printed by Multiplex techniques lid, St Marv Cray. Kent.