EP0504149A1

EP0504149A1 - Sensor for measuring force and/or travel and process for its manufacture

Info

Publication number: EP0504149A1
Application number: EP19900915746
Authority: EP
Inventors: Henderikus L. Offereins; Hermann Sandmaier
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 1989-12-08
Filing date: 1990-10-29
Publication date: 1992-09-23
Also published as: DE3940696C2; WO1991009288A1; DE3940696A1

Abstract

Dans un procédé pour la fabrication d'un capteur pour la mesure d'une force et/ou d'une course, lequel présente un corps de capteur (2, 2') avec un champ d'action (3) à structure plissée, les opérations de base suivantes sont effectuées: application de part et d'autre de couches résistant à un agent de gravure sur les surfaces principales d'une galette semiconductrice, réalisation d'ouvertures dans les deux couches au moyen d'un procédé par résine photosensible, gravure anisotrope sur les deux faces de creux essentiellement en V dans la galette semiconductrice, et subdivision de la galette semiconductrice en différents corps de capteur (2, 2').In a method for manufacturing a sensor for measuring a force and / or a stroke, which has a sensor body (2, 2 ') with a field of action (3) with a pleated structure, the following basic operations are carried out: application on both sides of layers resistant to an etchant on the main surfaces of a semiconductor wafer, making openings in the two layers using a photosensitive resin process , anisotropic etching on the two essentially V-shaped hollow faces in the semiconductor wafer, and subdivision of the semiconductor wafer into different sensor bodies (2, 2 ').

Description

Sensor for measuring a force and / or a path and method for producing the same

description

The present invention relates to a sensor for measuring a force and / or a path with at least one sensor body which has at least one transducer element with which a deformation of a deformable effective area of the sensor body can be detected, according to the preamble of claim 7, and a method for producing such a sensor according to the preamble of claim 1.

A known micromechanical sensor for measuring a force and / or a path is constructed as a bending beam sensor. A basic illustration of a bending beam sensor with a bending beam clamped on one side is shown in FIG. 1, while FIG. 2 shows an embodiment of a bending beam sensor with a bending beam clamped on both sides in the form of a basic diagram. Mechanical-electrical transducers are arranged on the upper side of the beam clamped on one or both sides of the beam facing the attacking force F or on the underside facing away from this upper side, converting an expansion or compression of the surface of the bending beam into an electrical signal. Both in the case of the force sensor based on the principle of the cantilever clamped on the one hand and the one based on the principle of the cantilever beam clamped on both sides, the force to be measured must be introduced into the sensor perpendicular to the longitudinal axis of the beam, making the required housing technology susceptible to failure, complex and expensive . Furthermore, the force sensor, on the principle of the cantilever clamped on one side, suffers from the disadvantage inherent in this principle that the force application point not only shifts with increasing force in the direction of action of the sensor, that is to say in the direction of the acting force, but is also shifted towards the clamping point of the bending beam with increasing force. Although it is possible to determine a fixed distance between the force application point and the clamping point of the cantilever clamped by a suitable design of the housing technology, this requires a design of the force introduction means that the force application point is seen relative to the canting beam with increasing force from the clamping point can move away. Naturally, this makes the structure of the force sensor complex, complicated and prone to failure.

Of course, the problem of shifting the force application point as a function of the applied force, which is inherent in the cantilever force sensor clamped on one side, does not occur in the case of a force sensor based on the principle of the cantilever beam clamped on both sides, as long as the force is in the center of the beam based on the clamping points. However, the deflection of the bending beam by the force here requires not only a bending of the beam, but also its extension, which results in a non-linear dependence of the output signal on the magnitude of the applied force.

Reference is made to the following references as printed proof of the prior knowledge of force sensors based on the principle of the one-sided or two-sided clamped bending beam:

1. K. Oppermann: A new Force Sensor with Metal Measuring Grid Transverse to the Lines of Force, Sensors and Actuators, 7, (1985), pp. 223-232.

2. D. Schubert: Piezoresistive Proprieties of Polycrystalline and Crystalline Silicon Films, Sensors and Actuators, 11, (1987), pp. 145-155. 3. B. Puers, W. Sanson: Assessment of Thick Film Fabrication Methods of Force (Pressure) Sensors, Sensors and Actuators, 12, (1987), pp. 57-76.

4. S. Pasczynski, J. Potencki, W. Kaiita: Free- End Beam- Type- Force- Sensor with Thick- Film Resistor as Strain- Sensitive Element: Towards an Optimum Construction, Sensors and Actuators, 17, (1989), Pp. 225-233.

5. F.R. Blom, S. Bouwstra, J.H.J. Fluitman, M. Elwenspoek: Resonating Silicon Beam Force Sensor, Sensors and Actuators, 17 (1989) pp. 513-519

6. J.W. Holm-Kennedy, M.H. Kaneshiro, G.P. Lee, Silicon Monolithic-Multidimensional Force-Sensors: Devices for Simultaneous Measurement of Multiple Force-Measurement, Transducers 89, Montreux, (1989).

DE-A-2264496, DE-A-2555231 and DE-B-1227261 show force sensor structures which have a double-U-shaped cross section or wrinkle-like cross section. However, these sensors are not suitable for microminiaturization.

DE-Al-3742673 shows a sensor consisting of a semiconductor material, which is U-shaped in cross section.

Starting from this prior art, the present invention is based on the object of developing a sensor of the type mentioned at the beginning and a method for its production in such a way that the sensor with linear dependence of the output signal on the applied force or the path to be recorded can be produced in a simple manner and can be carried out in a micro-miniaturized manner.

This object is achieved by a method according to claim 1 and by a sensor according to claim 7. The invention is based on the knowledge that the fold-like structure of the sensor in its effective area with at least two substantially perpendicular to the effective direction of the sensor, arranged on opposite longitudinal sides of the sensor and facing each other in the effective direction of the sensor offset recesses leads to a sensor body structure that can be produced using methods of micromechanics and has a stable active geometry that is only acted upon in its longitudinal direction or active direction. Because of its suitability for micromechanical manufacturing processes in photoetching technology, such a structure is not only highly precise, but also enables mass production at low costs. Furthermore, the sensor according to the invention is suitable for installation in a simple housing, since elongations of the sensor body only occur in the direction of action of the applied force. In contrast to the force sensors known in the prior art based on the concept of the bending beam, there is therefore no change in the force application point. By varying the number and dimensions of its fold-like structures, the sensor according to the invention enables the force or displacement ranges of the sensor to be set over a wide range.

Preferred embodiments of the sensor according to the invention are explained in more detail below with reference to the accompanying drawings. Show it:

3 shows a first embodiment of the sensor according to the invention;

4 shows a second embodiment of the sensor according to the invention;

5 shows a third embodiment of the sensor according to the invention; and

6 shows an action diagram for explaining the action geometry the embodiment of the sensor according to the invention shown in FIGS. 4 and 5.

The sensor shown in FIG. 3 is designated in its entirety by reference number 1 and comprises a sensor body 2, which in turn comprises an effective area 3 and two end parts 4, 5 adjoining the effective area on its two sides in the effective direction. Notches 6, 7, 8, 9 are provided on the two end parts 4, 5 for mounting the sensor 1 and for applying force to the sensor. In the embodiment shown in FIG. 3, the sensor body 2 has five recesses 10, 11, 12, 13, 14 in its active region 3, which extend perpendicular to the active direction of the sensor 1. Three of the recesses 10, 12, 14 lie on a first longitudinal side 15 of the sensor body 2 and extend in the direction of the other longitudinal side 16 of the sensor body 2 until just before this, while the other two recesses 11, 13 differ from the extend from the second long side 16 in the direction of the first long side 15 to just before this. The recesses 10, 12, 14, which extend from the first longitudinal side 15 into the sensor body 2, are arranged alternately with the recesses 11, 13, which extend from the second longitudinal side 16 into the sensor body 2 and in such a manner Longitudinal direction or direction of action of the sensor body 2 offset from one another that transverse wall elements 17, 18, 19, 20 are defined between the mutually opposite recesses 10, 11, 12, 13, 14, which are at a predetermined angle to the direction of action of the sensor 1 extend from one longitudinal side 15 to the other longitudinal side 16 thereof. Between two transverse wall elements 17, 18; 18, 19; 19, 20 each have a longitudinal wall element 21, 22, 23 which extends in the direction of action of the sensor 1 and forms part of one of the two long sides 15, 16 of the sensor body 2.

The transverse wall elements 17, 18, 19 together with the longitudinal wall elements 21, 22, 23 define a wrinkle-like structure with them transversely in the effective area 3 of the sensor body 2 the direction of action of the sensor 1 extending folds.

Mechanical-electrical transducer elements, which are designed as transverse, piezoresistive resistors 24, 25, are arranged on two longitudinal wall elements 21, 23. When the sensor 1 is subjected to tensile stress, these resistances respond to the shortening of the surface of the longitudinal wall elements 21, 23, which is caused by a bending of the longitudinal wall elements 21, 23 about an axis extending perpendicular to the direction of action. The transverse, piezoresistive resistors 24, 25 are connected by conductor tracks 26, 27; 28, 29 with connections 30, 31; 32, 33 in connection, which are arranged on a longitudinal side 15 of the end parts 4, 5. These connections 30, 31, 32, 33 can be connected with wires which are fastened to the connections 30 to 33 by means of the usual bonding technique.

The manufacture of the sensor 1 shown in FIG. 3 is explained below. A silicon wafer with the crystal orientation (100) serves as the starting material for the production of this sensor 1. After thermal oxidation of the wafer, it is structured using a photoresist process for the subsequent implantation of the piezoresistors. This is followed by annealing of the silicon wafer structure and passivation of its surface by means of oxidation and a subsequent nitride deposition in the chemical vapor deposition process at low pressure (LPCVD) on the front and on the back of the wafer. After vapor deposition of a metallization consisting, for example, of aluminum, it is structured by means of a further photoresist process for the production of the electrical contacts to the resistors.

After a photoresist process on both sides, the oxide and the nitride are opened at the points at which the V-shaped recesses 10 to 14 are later to be produced. The V-shaped recesses are produced in an anisotropic etching process, as a result of which the geometry of the sensor body 2 is set.

In a further method step, the conductor tracks 26 to 29 to the connections 30 to 33, which can be embodied as bond contacts, are produced in a laser-induced deposition process. A plasma nitride layer is deposited as the final passivation layer.

In a last process step, the individual sensors 1 are separated from the silicon wafer by sawing.

The embodiment of the sensor 1 according to the invention shown in FIG. 4 largely corresponds structurally and in terms of its manufacturing method to the sensor according to FIG. 3, so that only structural and manufacturing deviations from the first embodiment according to FIG. 3 are to be explained.

The second embodiment according to FIG. 4 consists of two sensor bodies 2, 2 ', which are each connected to one another on one 16 of their two longitudinal sides 15, 16 in the region of the end parts 4, 5 and in the region of the longitudinal wall elements 22 facing one another.

As is also evident from a comparison of FIG. 4 with FIG. 3, in the embodiment according to FIG. 4 each sensor body 2, 2 'has a notch 6 only on the longitudinal side 15 facing away from the other sensor body 2', 2, 8th; 6 ', 8' on.

The manufacturing method largely corresponds to that of the sensor according to FIG. 3, but in the embodiment according to FIG. 4 a pyrex layer is sputtered onto one of the two wafers after the method step of applying the plasma nitride layer by deposition and before the sensors are separated by means of sawing is before the two wafers are connected to one another on the back by means of the anodic bonding method. After this step of the Joining follows in accordance with the method described with reference to FIG. 3, the separation of the sensors 1 by means of sawing.

In the third embodiment according to FIG. 5, which corresponds to the second embodiment according to FIG. 4 with regard to the structure of the sensor body and with regard to its production method, the mechanical-electrical converter elements are resonators 34, 35, 36, 37, 38 , 39 executed. The resonators each extend in a bridge-like manner over the recesses 10, 12, 14; 10 12 14 ^λ . The resonators can be made of silicon with a (100) orientation. It is also possible to produce the resonators by depositing polysilicon or other materials. Since the manufacture and construction of such resonators is known per se, no detailed explanation in this regard is required. The resonators 34 to 39 will then be used as transducer elements when a particularly precise measurement is in the foreground and a higher manufacturing effort is justifiable.

6 illustrates the influence of a compressive force on the active geometry of a sensor according to the invention according to the second or third embodiment according to FIGS. 4 or 5. As can be seen from this figure, when a force is applied, the sensor structure becomes symmetrical to its longitudinal axis deformed like an accordion. The force application point moves relative to the clamping point of the structure only along the effective direction or longitudinal axis of the structure, so that the problems of the prior art explained at the outset do not occur with the sensor structure according to the invention.

In a departure from the embodiments according to FIGS. 3 to 5, it is possible to dispense with the arrangement of conductor tracks 26 to 29 provided there on the transverse wall elements 17 to 20 and to make wire contacting at the location of the resistors 24, 25. A detector can also tation of the deformation directly on these resistors 24, 25 take place.

In the exemplary embodiment described, the recesses are described as essentially V-shaped. Depending on the etching characteristic of the starting material used, other longitudinal cut-outs may also result, which may be substantially U-shaped, for example.

In the exemplary embodiment described, the sensor bodies 2 consist of silicon. Instead of silicon, however, other etchable materials, in particular semiconductor materials, can also be used.

In the described embodiments, the fold structure is defined by five alternating recesses. Depending on the desired length of the fold structure and on the desired elasticity and desired measuring path, the number of folds defined by the recesses can also be selected to be higher or lower.

In the method explained with reference to FIG. 4, the two wafers are connected to one another using an anodic bonding method. Instead of this method, the so-called silicone fusion bonding method can also be used for connecting the two wafers. The two wafers can also be connected to one another by soldering, gluing or alloying.

In deviation from the exemplary embodiment described, an optoelectronic transducer arrangement can also be used as the transducer element, which has a light source for generating a light beam, which furthermore has a mirror surface arranged on the deformable active region for reflecting the light beam and an opto includes electronic sensor for detecting the deflection of the light beam. The light source here is preferably a laser light source. A particularly simple deflection of the light beam through the mirror surface is achieved in that one of the transverse wall elements is provided with the mirror surface. The mirror surface can be produced by applying a reflective coating to the transverse wall element. The optoelectronic sensor can be both a sensor that detects the deflection of the light beam in an analog or quasi-analog manner and a sensor that can only digitally detect the impact of the light beam on a predetermined one Detection area or its distraction from this detection area.

Claims

1 1Patent claims

1. A method for producing a sensor for measuring a force and / or a path, with at least one sensor body which has at least one transducer element with which a deformation of a deformable effective area of the sensor body can be detected, the sensor body in its effective area at least two recesses which extend substantially perpendicular to the direction of action of the sensor and are arranged on opposite longitudinal sides of the sensor body and offset from one another in the direction of action of the sensor and which define a wrinkle-like structure of the sensor body in its area of action,

characterized by the following process steps:

- Applying layers resistant to an etchant on both sides to the main surfaces of a semiconductor wafer;

- Creation of openings in the two layers by means of a photoresist process;

anisotropic double-sided etching of essentially V-shaped recesses in the semiconductor wafer; and

- Subdivide the semiconductor wafer into sensor body.

2. The method according to claim 1, characterized in that

that the process step of applying layers resistant to an etchant on both sides comprises the following substeps: Passivation of the two main surfaces of the semiconductor wafer by thermal oxidation; and

- Deposition of a nitride layer on the two main surfaces of the semiconductor wafer.

3. The method according to claim 2, characterized in that

that the step of depositing a nitride layer comprises depositing a nitride layer in the chemical vapor deposition process at low pressure.

4. The method according to any one of claims 1 to 3, gekennzeich¬ net by the following initial process steps:

- thermal oxidation of the semiconductor wafer;

Patterning the surface of the semiconductor wafer by means of a photoresist process;

- implanting piezoresistors; and

- Healing the semiconductor wafer.

5. The method according to any one of claims 1 to 4, gekennzeich¬ net by the following process steps after Aufbrin¬ gene of the layers resistant to an etchant:

- vapor deposition of a metallization;

- Structuring of the metallization by means of a further photoresist process for producing electrical contacts to the piezoresistors.

6. The method according to any one of claims 1 to 5, gekennzeich¬ net by the following method steps after creating the V-shaped recesses by anisotropic etching on both sides: - Laser-induced deposition of conductor tracks on transverse wall elements of the fold-like structure of the sensor body in its effective range; and

- depositing a passivation layer.

7. Sensor for measuring a force and / or a path, with at least one sensor body (2, 2 ') which has at least one transducer element (24, 25; 34, 35, 36, 37, 38, 39) with which one Deformation of a deformable effective area (3) of the sensor body (2, 2 ') can be detected,

wherein the sensor body (2, 2 ') has in its effective area (3) at least two substantially perpendicular to the effective direction of the sensor (1), arranged on opposite longitudinal sides (15, 16) of the sensor body (2, 2') and has recesses (10, 11, 12, 13, 14) which are offset from one another in the direction of action of the sensor (1) and which define a fold-like structure of the sensor body (2) in its area of action (3),

characterized,

that the sensor body (2, 2 ') consists of a semiconductor material at least within its effective range (3),

that the recesses (10, 11, 12, 13, 14) are essentially V-shaped by anisotropic etching,

that the sensor body (2) has two end parts (4, 5) adjoining its effective areas (3) for the introduction of force and at least one unit within its effective area from a transverse wall element (17 , 18, 19, 20) and an adjoining one, extending in the effective direction and a long side of the sensor has body-forming longitudinal wall element.

8. Sensor according to claim 7, characterized in

that the sensor (1) comprises two sensor bodies (2, 2 '), each on one (16) of their longitudinal sides (15, 16) in the region of the end parts (4, 5) and in the region of the longitudinal wall elements (22 ) are connected.

9. Sensor according to claim 7 or 8, characterized in

that the mechanical-electrical transducer element (24, 25) on the longitudinal wall element (21, 22, 23) is arranged such that a shortening or elongation of the surface of the longitudinal wall element (21, 22, 23) in the effective direction due to a from a force in the bending of the longitudinal wall element (21, 22, 23) resulting from the effective direction of the sensor (1) can be detected about an axis extending perpendicular to the effective direction.

10. Sensor according to one of claims 7 to 9, characterized in that:

that the mechanical-electrical transducer element is formed by a transverse, piezoresistive resistor (24, 25).

11. Sensor according to claim 9 or 10, characterized in that

that the mechanical-electrical transducer element (24, 25) arranged on the longitudinal wall element (21, 22, 23) via conductor tracks (26, 27, 28, 29), that via the transverse wall element (17, 18, 19, 20 ) run, is connected to one of the two end parts (4, 5) arranged connecting contacts (30, 31, 32, 33).

12. Sensor according to claim 7 or 8, characterized. that the mechanical-electrical transducer element is formed by a resonator structure (34, 35, 36, 37, 38, 39) that extends like a bridge over one of the recesses.

13. Sensor according to claim 7 or 8, characterized in

that the converter element has a light source for generating a light beam, a mirror surface arranged on the deformable active region for reflecting the light beam and an opto-electronic sensor for detecting a deflection position of the light beam.

14. Sensor according to claim 13, characterized in

that the light source is a laser light source.

15. Sensor according to claim 13 or 14, characterized in that

that the mirror surface is arranged on one of the transverse wall elements (17, 18, 19, 20).