Detection device with a hanging piezoresistive strain gauge comprising a strain amplification cell

TECHNICAL FIELD AND PRIOR ART

p0001The invention relates to the field of microcomponents or nanocomposites, including silicon, for example inertial sensors, including accelerometers, gyrometers or force sensors, resonant chemical sensors and resonators.

p0002It finds application in varied fields, such as automotive, mobile and avionics, to form such a time base or perform a mechanical filtering.

p0003In known manner, resonant sensors can be achieved:<ul><li>either volume technology, in which case the sensor element is formed over the entire thickness of a silicon or quartz substrate by the steps of wet etching,</li><li>either on the surface of technology, in which case the silicon substrate is machined only on a fraction of its thickness, for example between a few microns and a few tens of micrometers. The document<nplcit id="ncit0001" npl-type="b"><text>"Resonant accelerometer with self-test," Mr. Aikele et al., Sensors and Actuators A 92 (2001), Elsevier, pages 161-167</text></nplcit>Discloses an example of such a resonating sensor.</li></ul>

p0004In an inertial resonant realized in surface technology sensor, the resonator vibrates in the plane of the substrate and excitation / detection electrodes are obtained by plasma etching DRIE (deep reactive ion etching) in the substrate. Machining by DRIE etching plasma and then the release of the sensor elements by etching a sacrificial layer used to optimize the design ( "design") of the sensor, and in particular to bring the resonator of recessed hinges, or anchoring, connecting it to the rest of the substrate.

p0005In a resonant sensor based on silicon, the detection of the vibration is carried out by electrostatic means, the piezoresistive means implanted resistors or by piezoelectric means. Or, in the case of a miniaturization of this type of sensor, for example in the context of the realization of NEMS (nanoelectromechanical systems), these types of detection become problematic because of the very low capacitance measurement in the case of an electrostatic detection, the difficulty in producing piezoresistive gauges by implantation, or of the problem, in the case of piezoelectric gauges, linked to the deposition of a piezoelectric material of the resonator, leading to a lower quality factor.

p0006In the case of resonant sensors with piezoresistive detection type MEMS (microelectromechanical system), gauges located on the surface of a test body detect only a normal stress caused by out of plane bending movement, -to say normal to a plane of the substrate from which is made the sensor. That implies :<ul><li>severely limiting the possible designs of sensors, especially in the case of integrated bi-axial sensors such as inertial sensors,</li><li>poor adaptation to sensors made using surface technology,</li><li>poor adaptation to sensors "ultra-miniaturized," such as NEMS, as it is difficult to define with sufficient precision and without addition of mechanical stress due to the metallization on the test body, the doping zones and connectors, to achieve gauge bridges, on beams of a few tens of nanometers wide.</li></ul>

p0007The document <nplcit id="ncit0002" npl-type="s"><text>"High-fashion pizoresistive resonant cantilever sensors for tens-femtogram resoluble mass sensing in air" Dazhong Jin et al., 2006, J. Micromech. Microeng 16, 1017 pages 1023</text></nplcit>Discloses another type of sensor in which the piezoresistive gauges are produced by depositing a conductive layer over the resonator. But such a deposit can lead to several major drawbacks:<ul><li>adding constraints on the beam,</li><li>a lower resonator quality factor,</li><li>the occurrence of critical steps in addition to steps of realization of the actual resonator (depositing a very thin layer of conductive material with a very strict thickness control, alignment, photolithography and etching of the gauges on the beam)</li><li>a detection being made out of plane, which can be a disadvantage in terms of design, especially if one wishes to have an isolated electrostatic excitation of the substrate, for example in the case of a single crystal silicon resonator,</li><li>low piezoresistive coefficient (compared to a silicon gauge) inducing a lower sensitivity.</li></ul>

p0008The document <nplcit id="ncit0003" npl-type="s"><text>"Single-mask SOI manufacturing process for linear and angular piezoresistive accelerometers with on-chip reference resistors", J. Eklund et al., Sensors, 2005, IEEE, 30 October to 3 November 2005, pages 656-659</text></nplcit>Discloses another type of sensor in which the gauges are defined by etching the silicon. Silicon is not doped surface and detection (tension, compression) is in the plan. Such a configuration called suspended gauge, is well suited to surface technology and the realization of very small sensors (NEMS) compared to type gauges implanted or deposited. Against by, in the case of a small-sized sensor, having a small inertial mass, the sensor sensitivity is low.

PRESENTATION OF THE INVENTION

p0009An object of the present invention is to provide a device, or microcomponent or nanocomponent, sensor type and / or resonator, advantageously made of surface technology, with sensitivity and high accuracy (signal / high noise, low temperature drift ), adaptable to NEMS, that is to say sensors of very small dimensions (nanometer scale).

p0010To solve these problems, the invention proposes to provide a device, or microcomponent or nanocomponent at piezoresistive detection advantageously made surface technology, comprising at least:<ul><li>a test body in which exerts a force to be measured,</li><li>means for detecting a strain exerted by the proof body under the action of the effort, comprising at least one suspended piezoresistive strain gauge,</li><li>a strain amplifier cell comprising at least two rigid arms mechanically linked to each other by at least one connecting member at a first of their ends, a second end of a first of the two rigid arms being mechanically linked to the proof body, a second end of a second of the two rigid arms being anchored to a substrate, said connecting member, or the first ends of the two rigid arms being mechanically connected to a first end of the dipstick of suspended piezoresistive strain.</li></ul>

p0011mechanical element test body means capable of deforming under the effect of an external stress (acceleration, pressure, temperature, ...). For example, in the case of inertial sensors, the test body may correspond to one or more seismic masses. In the case of a resonator or resonant sensor, the test body may correspond to one or more resonant structures, also called resonators.

p0012When the device is of resonator or resonant sensor types, only the frequency of the piezoresistive signal is detected across the suspended piezoresistive strain gauge, and not its amplitude. This takes advantage of both the high sensitivity of the frequency change detection, and the simplicity of implementation of the piezoresistive detection.

p0013In addition, with this type of device can be dispensed with metallization of the resonator or an implementation of the gauge, which are very demanding technical from a technological perspective can also degrade device performance.

p0014The invention can be used to perform an oscillator, a resonator or any resonant or non-sensor (accelerometer, gyroscope, pressure sensor, mass or biochemical ...).

p0015When the device is not of resonator or resonant sensor type, amplification cell can also transmit the amplitude of the detected signal piezoresistive.

p0016The structure in "half-jack" or chevron of the amplification cell formed by the rigid arm allows for the necessary connections to the piezoresistive measuring, preferably in gauge bridge or Wheatstone bridge, since the ends of the gauge is thus fixed to the substrate.

p0017The structure is adapted to a "surface technology" type of manufacturing, applicable to MEMS or NEMS type components. The test body, the detecting means, that is to say at least the suspended piezoresistive strain gauge, and the elements of the strain amplifier cell can be made in the same plane, that is ie all have a common plan. In addition, the strain gauge and the test body may be formed in a same piezoresistive material.

p0018The amplifier cell can be advantageously used for detecting the frequency of vibration of a resonant beam, but also of any vibrating structure forming a test body, thus providing maximum freedom as regards the design of the device.

p0019The suspended piezoresistive strain gauge may comprise a second end anchored to the substrate.

p0020The suspended piezoresistive strain gauge may comprise at least one suspended beam based on a piezoresistive material.

p0021Advantageously, the device may comprise at least two piezoresistive gauges constraints suspended, thereby achieving a differential measurement. In general, the amplification cell can be used differentially on a resonant structure or not, or on two differentially mounted sensors.

p0022Advantageously, the second end of the first rigid arm may be linked to the proof body in the vicinity of an embedment of the proof body to the substrate.

p0023The connecting element mechanically linking the two first ends of the two rigid arms may comprise at least one pivot link.

p0024The link mechanically linking the first member ends of the two rigid arms may have a fixed connection with the first end of the suspended piezoresistive strain gauge.

p0025In this case, each of the first ends of the two rigid arms can be mechanically connected to the connecting element by at least one pivot link.

p0026The two rigid arms may be symmetrical with respect to a principal axis of the suspended piezoresistive strain gauge.

p0027The test body may comprise at least one mobile seismic mass in the plane of the substrate, which can be connected to the second end of the first rigid arm.

p0028The seismic mass may be anchored to the substrate via a hinge.

p0029The seismic mass may be fixed to the substrate by means of a guiding arm formed in the seismic mass and embedded in the substrate.

p0030Alternatively, the test body may comprise at least one resonant element flexing in the plane of the substrate. The resonant element may be beam or tuning fork.

p0031The device may further comprise excitation means of the resonant element, capacitive, and / or piezoelectric, and / or mechanical and / or thermo.

p0032Both ends of the resonant element may be anchored to the substrate.

p0033The test body may further comprise at least one mobile seismic mass in the plane of the substrate, connected to the resonant element.

p0034The seismic mass may be anchored to the substrate via a hinge.

p0035The resonant element can be connected to the seismic mass in the vicinity of an embedment of the seismic mass to the substrate.

p0036The test body may comprise at least two mobile seismic masses in the plane of the substrate, two link arms linked to each of the two seismic masses through flexing arms intended to transmit the movements of the seismic masses to the link arms , the second end of the first rigid arm of the strain amplifier cell being connectable to one of the connecting arms in the vicinity of an embedment of said link arms to the substrate.

p0037In this case, the link arms and the flexing arms may form for example a substantially rectangular frame.

p0038The device may further comprise excitation means of the seismic masses of electrostatic type and / or thermal and / or piezoelectric.

p0039The device may further comprise at least one second strain amplifier cell may comprise at least two rigid arms mechanically linked to each other by at least one connecting member at a first end thereof a second end of a first of the two rigid arms being mechanically linked to the proof body, a second end of a second of the two rigid arms being fixed to the substrate, said connecting member, or the first ends of the two rigid arms which can be mechanically connected to a first end of a second suspended piezoresistive strain gauge intended to work in differential manner in compression or tension in relation to the first suspended piezoresistive strain gauge working in tension or compression, respectively.

p0040The device may further comprise at least two resistive elements and a polarization source capable of forming, with the other elements of the device, a Wheatstone bridge.

p0041The device may further comprise means for measuring the variation of the resistance of the suspended piezoresistive strain gauge.

p0042The or piezoresistive strain gauges suspended may be arranged perpendicularly to the axis of the induced effort (for example acceleration or rotation) to be measured.

p0043The device may be a sensor such as an accelerometer or a gyroscope, resonant or unsubstituted, or a resonator.

p0044The present invention also relates to a method for producing a device, or microcomponent or nanocomponent, as described above, comprising at least the steps of:<ol><li>a) depositing a layer based on at least one conductive material (e.g., titanium tri-layer of nickel and gold) on a substrate having a first layer based on at least one semi -conducteur on which is disposed a sacrificial layer and a second layer based on semiconductor,</li><li>b) photolithography and etching of electrical contacts of the device into the base of the conductive material layer,</li><li>c) photolithography and etching of the mechanical structure of the device in the second layer based on semiconductor, stopping on the sacrificial layer,</li><li>d) release of the elements of the device by etching the sacrificial layer in these elements.</li></ol>

p0045The substrate used may for example be an SOI (silicon on insulator).

p0046The method may further comprise, between steps b) and c), the steps of: <ul><li>deposition, for example by photolithography, of a protective layer on the mechanical structure of the device, except on the suspended piezoresistive strain gauge,</li><li>thinning, for example by etching with stoppage at the end of a fixed term of the suspended piezoresistive strain gauge,</li><li>removing the protective layer.</li></ul>

BRIEF DESCRIPTION OF DRAWINGS

p0047The invention will be better understood from reading the description of embodiments given purely indicative and non-limiting with reference to the accompanying drawings, wherein:<ul><li>the <figref idrefs="f0001">figure 1</figref> represents a resonator with electrostatic excitation and suspended piezoresistive detection comprising a strain amplifier cell, object of the present invention,</li><li>the <figref idrefs="f0001">2</figref> represents a resonant accelerometer detection by suspended piezoresistive strain gauge comprising a strain amplifier cell, object of the present invention,</li><li>the <figref idrefs="f0002">3</figref> represents a resonant gyro detection by suspended piezoresistive strain gauge comprising a strain amplifier cell, object of the present invention,</li><li>the <figref idrefs="f0002">4</figref> represents a non-resonant detection by suspended piezoresistive strain gauge accelerometer comprising a strain amplifier cell, object of the present invention,</li><li>the <figref idrefs="f0003">5</figref> shows a strain amplifier cell comprising an electrical track carried on a rigid arm of the cell,</li><li>the <figref idrefs="f0003">6</figref> represents a non resonant accelerometer detection by suspended piezoresistive strain gauge comprising a strain amplifier cell, object of the present invention,</li><li>the <figref idrefs="f0004">7</figref> represents a resonator detection by suspended piezoresistive strain gauges mounted in differential mode and in a Wheatstone bridge comprising two strain amplification cells, object of the present invention,</li><li>the <figref idrefs="f0004">8</figref> represents a non resonant accelerometer by detecting strain gauges mounted suspended piezoresistive differential mode and the Wheatstone bridge, and comprising two strain amplification cells, object of the present invention,</li><li>the <figref idrefs="f0005">9A</figref> represents an accelerometer with detection by piezoresistive strain gauges suspended differential mode and mounted to a Wheatstone bridge comprising two strain amplification cells, object of the present invention,</li><li>the <figref idrefs="f0005">9B</figref> represents an equivalent electrical diagram of the Wheatstone bridge formed by the accelerometer shown in <figref idrefs="f0005">9A</figref>, </li><li>the <figref idrefs="f0006">10A to 10C and 10A 'to 10C'</figref> show the steps of a first exemplary embodiment of the invention method, respectively in sectional views and top,</li><li>the <figref idrefs="f0007 f0008">11A to 11F and 11A 'to 11F'</figref> show the steps of a second example method embodiment of the invention, respectively in sectional views and top.</li></ul>

p0048Identical, similar or equivalent different figures described hereafter bear the same numerical references so as to facilitate the transition from one figure to another.

p0049The different parts shown in the figures are not necessarily to a uniform scale, to make the figures more legible.

p0050The various possibilities (variants and embodiments) should be understood as not being exclusive of each other and can be combined together.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

p0051firstly refers to the <figref idrefs="f0001">figure 1</figref> which represents a microcomponent 100 according to a first embodiment.

p0052In this first embodiment, the micro 100 is a resonator type MEMS or NEMS. The resonator 100 includes a resonant element 102, or resonant structure, eg, beam type, bending in a plane (x, y) corresponding to the plane of a substrate (not shown) from which the resonator is made 100. In Alternatively, the resonant element 102 may be of tuning fork type, that is to say formed by at least two beams connected to each other at one of their ends. The resonating element 102 is intended to be excited by excitation means 104, for example an excitation electrode. These excitation means 104 may be of the capacitive type, and / or piezoelectric, and / or magnetic and / or thermoelastic.

p0053The resonating element 102 is secured via a pivot connection, from one end, called second end, a first rigid arm 106, near a first recess 108 from a first end of the resonant element 102 to the substrate on which is formed the resonator 100, thereby limiting the contribution of the first rigid arm 106 to the natural frequency of the resonant element 102. the distance between the first recess 108 of the resonant 102 and the pivot connection element between the resonant element 102 and the first rigid arm 106 is for example equal to about one tenth of the length of the resonant element 102. a second end of the resonant element 102 is connected to a second recess 109 to the substrate. A first end of the first rigid arm 106 is linked by a pivot connection to a connecting element 110, having a rigid or fixed connection with a suspended piezoresistive strain gauge 112 thus providing the recessed-recessed boundary conditions of the gauge 112, the same time that the optimal transmission of the stress from the resonant element 102 and then amplified by the first rigid arm 106, the gauge 112. the gauge 112 is for example made by etching a beam suspended in a piezoresistive material, preferably doped silicon, to reduce the value of the resistance of the gauge 112. the other end of the piezoresistive gauge 112 is bonded to the substrate via a third recess 114 in the substrate also connected to measuring means 116 of the change in resistance .DELTA.R of the gauge 112.

p0054The resonator 100 further comprises a second rigid arm 118 whose first end is connected, via a pivot connection, to the connecting element 110, and a second end is connected, via a another pivot connection, a fourth recess 120 to the substrate. Each of the four recesses in substrate 108, 109, 114 and 120 form a fixed connection with the substrate on which is formed the resonator 100.

p0055The two rigid arms 106 and 118 are placed so as to constitute one half of a "jack" or chevron. The two rigid arms 106 and 118, and connecting element 110 form a strain amplifier cell of the resonator 100. All the elements of the resonator 100, apart from the recesses 108, 109, 114 and 120, are e.g. released from the substrate by etching a sacrificial layer disposed beneath the layer in which are formed the elements of the resonator 100.

p0056When the resonant element 102 is subjected to a bending force parallel and in the opposite direction to vector y (shown in <figref idrefs="f0001">figure 1</figref>), The resonant element 102 flexes in the direction of this force and then transmits a stress in the direction opposite to the vector y at the end of the first rigid arm 106. This stress applied to the first rigid arm 106 translates a movement stress in the direction opposite to the vector y and a constraint in rotation of the first rigid arm 106 in the counterclockwise direction around the pivot links connecting its ends to the connecting element 110 and resonance element 102, thereby reducing the value of the angle α, angle formed between a vector parallel to the x and the axis of the rigid arm 106. the connecting element 110 thus undergoes a strain in the direction of the vector x resulting in a compression force in the axis of the gauge 112.

p0057Conversely, when the resonant element 102 is subjected to a bending force and parallel in the direction of the vector y, the resonant element 102 flexes in the direction of this force, and transmits a strain in the direction of the vector y at the first end of the rigid arm 106. This stress applied to the rigid arm 106 results in a stress parallel travel and in the direction opposite to the vector x, and a rigid arm rotation restraint 106 in a clockwise direction about pivot connections between its ends connected to the connecting element 110 and the resonant element 102, increasing the value of the angle α. The connecting element 110 thus undergoes a strain in the direction opposite to the vector x resulting in an extension force in the axis of the gauge 112.

p0058The second rigid arm 118 supports, in a motion complementary to that of the first rigid arm 106, the axial displacements of the connecting member 110.

p0059Thus, the alternating flexing movement parallel to the vector y of the resonant element 102 results in an alternative variation of the resistance of the gauge 112 due to displacement stresses parallel to the x vector experienced by the gauge 112. The rigid arm 106 and 118 enable therefore amplify the bending stresses to the resonant element 102 and then applying them to the connecting element 110 and on the gauge 112. the two rigid arms 106, 118 and the connecting member 110 thus form a cell 'strain amplifier.

p0060The amplification ratio of the displacement of the resonant element 102, along the axis of the vector y, and the connecting member 110 along the axis of the vector x being about <i>1</i>/<i>tan (</i>α<i>)</i>, Preferably chosen to make the most of the amplification effect, an α of less than about 45 °.

p0061Preferably, the or rigid arms 106, 108 includes a relatively wide body with thin ends being deflectable relative to the body, thereby ensuring at least in part the pivot links. For example, in the case of a MEMS device, to a rigid arm body whose width is equal to about 10 .mu.m, the ends of the rigid arm can have a width equal to about 2 microns.

p0062Finally, variations in the resistance value of the gauge 112 are directly proportional to the longitudinal stresses which it is subjected, it is appropriate to maximize the detection sensitivity of the gauge 112, to reduce as much as possible the section of the gauge 112 within the limits of its compressive buckling stress. Typically, the value of this section can be less than the value of the rigid arm section 106, 118, at their center portions (body). The section of the gauge 112 may be even thinner in the thickness (dimension normal to the plane (x, y)), and be of a thickness less than those of other elements of the resonator 100.

p0063Referring now to <figref idrefs="f0001">2</figref> which represents a microcomponent 200, here a resonant sensor according to a second embodiment.

p0064The resonant sensor 200, here of the accelerometer type, comprises a resonant member 102 of its ends one of which is fixed to the substrate on which is formed the sensor 200, via a first recess 108, and attached at its other end to a seismic mass 202, in the vicinity of a hinge 204 connecting the seismic mass 202 to a second recess 206 to the substrate. The sensor 200 also includes excitation means 104, for example electrostatic, here an electrode, of the resonant element 102, an amplifier cell formed by two rigid arms 106, 118 and a connecting member 110 connected to a first end of a suspended piezoresistive strain gauge 112 which is also connected, at a second end to a fitting 114. the third amplification cell and the gauge 112 are disposed adjacent the first recess 108 of the element resonant 102. Finally, the sensor 200 comprises a measuring means 116 changes in .DELTA.R resistance of the gauge 112.

p0065In the case of a γ acceleration (shown in <figref idrefs="f0001">2</figref>), In the direction of the vector y, the seismic mass 202 is subjected to a force along the y axis which tends to rotate the rotating mass in the hinge 204, resulting in a constraint F (also shown in <figref idrefs="f0001">2</figref>) On the resonant element 102 in the direction opposite to the vector x. This constraint F induces a specific variation of the resonant frequency of the resonant element 102. The frequency of the resonant element 102 is then changed by the stress on the resonant element 102. The detection of the vibration is carried out by the gauge 112, the strain on the gauge 112 is amplified by the amplifier cell.

p0066In the examples described above, the amplification cell is advantageously used to amplify the strain, resulting from the vibration of the resonant element, the gauge 112. In an alternative embodiment, this amplifier cell can be used to measure the resonant frequency of any other resonant element, by judiciously choosing the locations of the resonant element at which the amplification cell is connected, advantageously near housings of the resonant element.

p0067The <figref idrefs="f0002">3</figref> represents a microcomponent 300, here a resonant gyroscope according to a third embodiment. The gyroscope 300 includes a substrate, not shown, and two seismic masses 302 movable in the plane (x, y) of the substrate and able to come into vibration. Two connecting arms 304, here parallel with respect to each other, are connected to the seismic mass 302 via the flexure arms 306 whose flexibility is sufficient to allow relative movements of the two seismic masses 302 relative to the link arms 304, while being sufficiently rigid to transmit the movements of the two seismic masses 302 to link arm 304. the link arm 304 and the flexing arms 306 here form a rectangular frame.

p0068The gyro 300 also includes excitation electrodes 308, for example in the form of combs whose fingers interlock with those of the seismic masses 302, adapted to put the seismic masses 302 vibrate in the plane (x, y), and particularly in a direction parallel to the x vector. Other means may be envisaged, for example electromagnetic means.

p0069The seismic masses 302 are energized, preferably at their resonant frequency or near this resonance frequency, by means of electrostatic forces applied through the electrodes 308. The seismic masses 302, the connecting arms 304 and flexure arms 306 form an excitation resonator. Operation at resonance provides a high amplitude of displacement of the seismic masses 302 (because the resonator quality factor), thus increasing the sensitivity of the gyroscope 300. Advantageously, the vibration of each of the seismic masses 302 may be in phase opposition with the vibration of another seismic mass 302, that is to say that their movements are opposite direction at any moment.

p0070When the gyroscope 300 undergoes an angular displacement around an axis z perpendicular to the substrate on which is formed the gyro 300, a Coriolis force is generated on each of the seismic masses 302, parallel to the vector y, after the composition of the vibration forced by the electrodes 308 with an angular velocity Ω. Coriolis forces are transmitted to the link arms 304 via the flexure arms 306. Each of the connecting arm 304 is connected to the substrate via a hinge 310. One of the link arm 304 is connected to the amplifier cell formed by the rigid arms 106, 118 and the connecting member 110 connected to the gauge 112, near a hinge 310. the change in resistance measured by the measuring means 116 is proportional to the angular velocity Ω relative to the rotation of the seismic masses 302 at the hinge 310.

p0071The amplification cell can also be used to achieve amplification of non-reciprocating (non resonant sensor), static or slowly varying, with great sensitivity, since being sized correctly, it increases significantly the signal amplitude piezoresistive obtained. Preferably in this type of sensor is performed in a temperature stability control of the suspended piezoresistive strain gauge so that temperature variations do not affect the resistance measurements.

p0072Referring to the <figref idrefs="f0002">4</figref> which represents a resonant sensor, here an accelerometer 400. The accelerometer 400 has a hinge 204 connecting a seismic mass 202 in a second recess 206 to the substrate. The accelerometer 400 also comprises an amplification cell formed by the rigid arms 106, 118 and the connecting member 110 connected to the suspended piezoresistive strain gauge 112. The rigid arm 118 of the amplification cell is anchored to the substrate via a recess 120, and the rigid arm 106 is attached to the proof mass 202 adjacent to the hinge 204. Under the effect of a γ acceleration, the seismic mass 202 applies a constraint on the arm F 106 of cell amplification in the opposite direction to the x axis, resulting in a ηF constraint, with η ≈ 1 / tan (α) on the gauge 112 along the y axis. The variation in resistance of the suspended piezoresistive strain gauge 112 is amplified by the amplifier cell, is then directly proportional to the acceleration. This variation is measured by the measuring means 116.

p0073Whatever the type of sensor and / or resonator, it is possible to perform measurements of changes in the resistance of the piezoelectric strain gauge suspended by connecting the measuring means directly to one end of the suspended piezoresistive strain gauge which is connected to a recess and a rigid arm of the amplifier cell is based on at least one semiconductor or conductive material. The fact that the measuring resistor is achieved through one of the rigid arm and the connecting element induces an additional series resistance slightly affecting the measurement.

p0074Alternatively, as shown in <figref idrefs="f0003">5</figref>, It is possible that electrical trace 122 is disposed on one of the rigid arms 118 of the amplification cell and at least partly on the connecting element 110, the measurement of resistance changes of the gauge 112 being performed via this electrical track 122. this variant is possible if the rigid arm 118 and the connecting member 110 are sufficiently broad to include such electrical trace 122, and that electrical trace 122 does not induce significant constraints on the structure of the amplification cell.

p0075The <figref idrefs="f0003">6</figref> represents a microcomponent 500 non resonant accelerometer type, according to another embodiment. This accelerometer includes an amplifier cell comprising the rigid arms 106, 118 and the connecting element 110. The accelerometer 500 also includes a seismic mass 502 in which is formed a guide arm 504 connected to a recess 506 on the substrate which is formed the accelerometer 500. the operation of this accelerometer is substantially similar to that described in connection with the<figref idrefs="f0002">4</figref>.

p0076The <figref idrefs="f0004">7</figref> represents a microcomponent 600 resonator type piezoresistive sensing differential mode uphill and Wheatstone bridge.

p0077The resonator 600 comprises a resonant member 102 of the beam type, excitation means 104, here an electrode, of the resonant element 102. As in the resonant device 100, the resonator 600 comprises a first amplification cell formed by two rigid arms 106, 118 connected to a connecting element 110 itself connected to a suspended piezoresistive strain gauge 112. This amplification unit is connected to a first end of the resonant element 102. the other end of the resonant element 102 is connected to a second amplification cell formed by a third rigid arm 106 'disposed between said other end of the resonant element 102, near a recess 108 at the substrate end, and a connecting element 110 'connected to a second suspended piezoresistive strain gauge 112'. A fourth rigid arm 118 'is disposed between a recess 120' to the substrate and the connecting element 110 '.

p0078The resonator 600 also includes other elements used to form a Wheatstone bridge, such as embedding the substrate 602, 604 and 606, resistive elements 608, 610, and a bias source 612. A voltage is measured between the recess 120 of the second rigid arm 118 and the recess 602 of one of the resistive elements 610. This results in a measurement of resistance R + .DELTA.R (.DELTA.R with variation in the resistance of the first suspended piezoresistive strain gauge 112) at of the first gauge pin 112, and a measuring resistor R-.DELTA.R (-ΔR with variation in the resistance of the second suspended piezoresistive strain gauge 112 ') at the second gauge 112'.

p0079There was thus a differential operation of a resonant structure mode, both amplification cells being complementary to achieve the amplification of movement of the resonant element 102.

p0080The <figref idrefs="f0004">8</figref> represents a microcomponent 700 of non resonant accelerometer type detection by suspended piezoresistive strain gauges assembled in differential mode and Wheatstone bridge.

p0081The accelerometer 700 includes the same elements as the resonator 600, except for the resonant element 102 and the excitation means 104 which are replaced by a seismic mass 202 which is fixed to the substrate by a recess 206 via a hinge 204. second ends of the rigid arms 106, 106 'are directly connected to the seismic mass 202.

p0082When the proof mass 202 is subjected to an acceleration γ in the direction of the y axis, the seismic mass exerts a 202 intensity constraint F / 2 voltage at the second end of the rigid arm 106 which is connected to the proof mass 202, in the direction of the x axis. The seismic mass also has another intensity constraint F / 2 in compression on the second end of the rigid arm 106 'which is connected to the seismic mass 202 in the opposite direction to the x axis. These constraints are reflected at the connecting elements 110 and 110 '. Thus, the gauges 112 and 112 'each undergo a strain in the direction of the y axis the intensity of which is equal to ηF / 2, η ≈ 1 / tan (α), α being the angle formed between the axis of the rigid arms 106, 106 'and a straight line parallel to the y axis.

p0083A voltage is measured between the recess 120 of the second rigid arm 118 and the recess 602 of one of the resistive elements 610. This results in a measurement of resistance R + .DELTA.R (.DELTA.R with variation in the resistance of the first gauge suspended piezoresistive strain 112) at the first gauge pin 112, and a measuring resistor R-.DELTA.R (-ΔR with variation in the resistance of the second suspended piezoresistive strain gauge 112 ') at the second gauge 112'.

p0084operation is thus a differential structure of a resonant mode, both amplifier cells being complementary to achieve the amplification of motion of the proof mass 202. The acceleration γ may be finally calculated conventionally from the parameters the elements forming the Wheatstone bridge.

p0085It is also possible to produce a microcomponent having a plurality of resonant and non-differentially mounted sensors. The<figref idrefs="f0005">9A</figref> shows an example of such microcomponent 800 from such non resonant accelerometer mounted differentially and in a Wheatstone bridge.

p0086The accelerometer 800 includes a first and a second non-resonant sensors 802, 804 of accelerometer type, for example similar to the accelerometer 400 shown in <figref idrefs="f0002">4</figref>. Each of the sensors 802, 804 comprises a seismic mass, a strain amplifier cell and of a suspended piezoresistive strain gauge. One of the rigid arms of the amplification cell of the first sensor 802 has a first end mechanically connected to a connecting element, itself connected to a strain gauge, and a second end electrically connected to a second end of a rigid arm of the second sensor amplifier cell. The other rigid arm of the amplification cell of the first sensor 802 has a first end connected to the connecting member and a second end connected to the seismic mass. One end of the strain gauge is electrically connected to a first resistive element 806 R and to one terminal of a bias source 808. A second resistive element R 810 is electrically connected to the first resistive element 806 and a R embedding of the suspended piezoresistive strain gauge of the second sensor 804.

p0087One of the rigid arms of the amplification cell of the second sensor 804 comprises a first end electrically connected to another connecting element, itself connected to one end of a strain gauge of the second sensor 804, and a second end electrically connected to the second end of one of the rigid arm of the strain amplifier cell of the first sensor 802. the other rigid arm of the amplification cell of the second sensor 804 has a first end connected to the connecting member and a second end connected to the seismic mass. One end of the strain gauge of the second sensor 804 is electrically connected to the second resistive element 810 and the other terminal of the bias source 808.

p0088Thus, the accelerometer elements 800 form a Wheatstone bridge circuit of a voltage being measured between a first point B where the two are connected resistive elements 806, 810, and a second point A is electrically connected to the second ends of two arms rigid strain amplifier cell of the two sensors 802 and 804. This measurement provides a measurement resistor R + .DELTA.R at the suspended piezoresistive strain gauge of the first sensor 802, and a measurement resistor R-.DELTA.R at the suspended piezoresistive strain gauge of the second sensor 804. It then deducted representative .DELTA.R value of γ acceleration experienced by the seismic masses of the sensors 802 and 804. the <figref idrefs="f0005">9B</figref> schematically shows the Wheatstone bridge obtained by mounting the <figref idrefs="f0005">9A</figref>.

p0089Referring now to <figref idrefs="f0006">10A to 10C</figref> (Sectional view) and 10A 'to 10C' (top view) showing the steps of a first embodiment of a microcomponents described previously.

p0090Is deposited for example a tri-layer (layer 3) based on titanium, nickel and gold, on an SOI substrate comprising a base substrate ( "bulk") 80 based on silicon, a sacrificial layer based on SiO₂ 81 (for example 0.4 microns thick) and a silicon layer 82 (e.g., 4 microns thick). Delineating contacts 83 by photolithography and etching (<figref idrefs="f0006">10A and 10A '</figref>).

p0091Then delineates the mechanical structure of the device by photolithography and DRIE etching, in the silicon layer 82, stopping on the sacrificial layer 81 (<figref idrefs="f0006">Figures 10B and 10B '</figref>).

p0092Finally, it releases the device components by exposure to hydrofluoric acid (humid or vapor) of the sacrificial layer 81 with stop after a fixed period.

p0093The device shown on <figref idrefs="f0006">Figures 10C and 10C '</figref> comprises a suspended piezoresistive strain gauge and an amplifier cell 85, a resonant element 86, a hinge 87, an excitation electrode 88 of the resonant element, and a seismic mass 89.

p0094The <figref idrefs="f0007 f0008">11A to 11F</figref> (Sectional view) and 11A 'to 11F' (top view) show the steps of a second embodiment of the microcomponents described previously.

p0095Depositing a titanium tri-layer of nickel and gold on a substrate for example of SOI for example similar to that described above. It defines the contact by photolithography and etching (<figref idrefs="f0007">11A and 11A '</figref>).

p0096Delineating the mechanical structure of the device by photolithography and DRIE etching of the mechanical structure in the silicon layer 82, stopping on the sacrificial layer 81 (<figref idrefs="f0007">Figures 11B and 11B '</figref>).

p0097Depositing a protective layer 84 of the mechanical structure by photolithography, except in a zone 90 where the piezoresistive strain gauge device is located (<figref idrefs="f0007">Figures 11C and 11C '</figref>).

p0098then thins the piezoresistive strain gauge 90 by DRIE etching stopping after a fixed period (<figref idrefs="f0008">Figures 11D and 11D '</figref>).

p0099There is provided a recess ( "stripping") of the protective layer 84 (<figref idrefs="f0008">Figures 11E and 11E '</figref>).

p0100It frees the components of the invention by exposure device in hydrofluoric acid (humid or vapor) of the sacrificial layer 81 with stop after a fixed period.

p0101The two embodiments described above are based on the use of SOI substrates based on monocrystalline silicon. However, this example is not restrictive and the microcomponents or nanodevices described above may be made from polysilicon-based substrate of monocrystalline SiGe, polycrystalline SiGe, etc ....