DE102022200489A1 - Micromechanical inertial sensor - Google Patents

Abstract

Micromechanical inertial sensor (100), comprising:- a substrate (1) with a first electrode (2); and- a seismic mass element (10), characterized in that a second electrode (3) is arranged within the seismic mass element (10), the second electrode (3) being bimetallic.

Description

The present invention relates to a micromechanical inertial sensor. The present invention also relates to a method for producing a micromechanical inertial sensor.

State of the art

Micromechanical inertial sensors for measuring acceleration and yaw rate are mass-produced for various applications in the automotive and consumer sectors. Rocker structures are preferred for capacitive acceleration sensors with a detection direction perpendicular to the wafer plane (e.g. in the z-direction). The sensor principle of these seesaws is based on a spring-mass system in which, in the simplest case, a movable seismic mass forms two plate capacitors with two counter-electrodes fixed on a substrate. The seismic mass is connected to the base via at least one torsion spring, usually two torsion springs for reasons of symmetry.

Homogeneous, temperature-dependent offset (temperature coefficient of offset, TCO, specified in mgal/K) as well as inhomogeneous, temperature gradient-dependent offset (temperature gradient of offset, TGO) of such inertial sensors are important performance parameters, which are important both in the design of MEMS cores as well as packaging. A reduction in the offset effects mentioned can be achieved, for example, by selecting a material (“a softer adhesive may transfer less stress”), chip design (“a thicker substrate may be more resistant to bending”) or core design (“higher sensitivity may make the sensor more accurate” ) take place.

Another way to prepare the sensors for temperature-induced errors is to use ASIC functionalities such as offset canceling. While these methods usually work well, in some cases their capabilities fall short. In addition, the performance of the ASIC is usually a bottleneck because only a limited number of functions can be implemented in the ASIC. An alternative solution can be a temperature-dependent trimming of the sensors.

Disclosure of Invention

It is an object of the present invention to provide an improved micromechanical inertial sensor.

• - ein Substrat mit einer ersten Elektrode; und
• - ein seismisches Massenelement, dadurch gekennzeichnet, dass innerhalb des seismischen Massenelements eine zweite Elektrode angeordnet ist, wobei die zweite Elektrode bimetallisch ausgebildet ist.

According to a first aspect, the object is achieved with a micromechanical inertial sensor, having:

• - a substrate with a first electrode; and
• - A seismic mass element, characterized in that a second electrode is arranged within the seismic mass element, the second electrode being bimetallic.

Changing temperature typically causes movement of the substrate and an electrode placed on the seismic mass. A compensation effect can advantageously be realized in this way. In this way, a bimetallic electrode structure for compensating for thermally induced deflection of the seismic mass is realized. The aforementioned temperature-dependent offset of the micromechanical MEMS sensor can be improved by means of the bimetallic electrode. The effect achieved is thus an electrode movement within the seismic mass and thus represents a kind of "coded TCO within the sensor".

• - Bereitstellen eines Substrats mit einer ersten Elektrode; und
• - Bereitstellen eines seismisches Massenelement, wobei innerhalb des seismischen Massenelements eine zweite, bimetallisch ausgebildete Elektrode angeordnet wird.

According to a second aspect, the object is achieved with a method for producing a micromechanical inertial sensor, having the steps:

• - providing a substrate having a first electrode; and
• - Provision of a seismic mass element, a second bimetallic electrode being arranged within the seismic mass element.

Preferred developments of the proposed micromechanical inertial sensor are the subject of dependent claims.

An advantageous development of the micromechanical inertial sensor is characterized in that the second electrode has oxide material enclosed in silicon material.

An advantageous development of the micromechanical inertial sensor is characterized in that the second electrode has at least one metal, in particular aluminum and/or nitride.

A further advantageous development of the micromechanical inertial sensor is characterized in that the second electrode is designed as a bar element which has plate-shaped elements spaced apart from one another on its underside. Is advantageous through this specific Shaping supports a slight deformability of the second electrode.

A further advantageous development of the micromechanical inertial sensor is characterized in that the first electrode is formed in a first functional layer. The proposed bimetallic behavior comes about through the mixture of different materials, which results in the advantageous effects.

A further advantageous development of the micromechanical inertial sensor is characterized in that the second electrode has at least a single block made of oxide material.

Further advantageous developments of the micromechanical inertial sensor are characterized in that the second electrode has at least two blocks of oxide material.

Further advantageous developments of the micromechanical inertial sensor are characterized in that at least one cavity is formed between the at least two blocks of oxide material. The resulting larger number of blocks of oxide material used means that the deformation is all the greater, as a result of which an efficient dimensioning tool is available.

Further advantageous developments of the micromechanical inertial sensor are characterized in that the inertial sensor is an in-plane sensor or an out-of-plane sensor.

The invention is described in detail below with further features and advantages on the basis of several figures. Elements that are the same or have the same function have the same reference symbols. The figures are intended in particular to clarify the principles which are essential to the invention and are not necessarily drawn to scale. For the sake of better clarity, it can be provided that not all of the reference symbols are drawn in in all of the figures.

Disclosed method features result analogously from corresponding disclosed device features and vice versa. This means in particular that features, technical advantages and embodiments relating to the micromechanical inertial sensor result in an analogous manner from corresponding embodiments, features and advantages of the method for producing a micromechanical inertial sensor and vice versa.

• 1 einen stark vereinfachten konventionellen mikromechanischen z-Inertialsensor mit asymmetrischer Wippenstruktur;
• 2 Ansichten eines vorgeschlagenen mikromechanischen Inertialsensors mit einer Erläuterung des dabei verwendeten Wirkungsprinzips;
• 3 eine perspektivische Ansicht eines bimetallischen Balkens, der den vorgeschlagenen Kompensationseffekt generiert;
• 4, 5 Querschnittsansicht ersten Ausführungsform des vorgeschlagenen mikromechanischen Inertialsensors;
• 6, 7 Querschnittsansicht einer zweiten Ausführungsform des vorgeschlagenen mikromechanischen Inertialsensors;
• 8, 9 Querschnittsansicht einer dritten Ausführungsform des vorgeschlagenen mikromechanischen Inertialsensors;
• 10 eine Draufsicht auf eine vierte Ausführungsform des vorgeschlagenen mikromechanischen Inertialsensors; und
• 11 einen prinzipiellen Ablauf eines Verfahrens zum Herstellen eines vorgeschlagenen mikromechanischen Inertialsensors.

In the figures shows:

• 1 a greatly simplified conventional micromechanical z-inertial sensor with an asymmetric rocker structure;
• 2 Views of a proposed micromechanical inertial sensor with an explanation of the operating principle used;
• 3 a perspective view of a bimetallic bar that generates the proposed compensation effect;
• 4 , 5 Cross-sectional view of the first embodiment of the proposed micromechanical inertial sensor;
• 6 , 7 Cross-sectional view of a second embodiment of the proposed micromechanical inertial sensor;
• 8th , 9 Cross-sectional view of a third embodiment of the proposed micromechanical inertial sensor;
• 10 a plan view of a fourth embodiment of the proposed micromechanical inertial sensor; and
• 11 a basic sequence of a method for producing a proposed micromechanical inertial sensor.

Description of Embodiments

1 shows a perspective view of a micromechanical inertial sensor 100 known per se with a seismic mass element 5 formed asymmetrically in a second functional layer 20 in the form of a rocker which is formed torsionally by means of a torsion element 4 (eg torsion spring). One recognizes first detection electrodes 2a, 2b formed in a first micromechanical functional layer 10, which interact with second electrodes 3a, 3b formed in a second functional layer 20. Such inertial sensors based on the rocker principle have a simple design and are widespread. However, a significant limitation of the offset stability can be caused by parasitic effects caused by bending of the substrate (not shown).

The basic structure of 1 is used to explain in detail a variant of the proposed sensor 100 in detail with reference to figures.

It is proposed to provide a bimetallic structure within a moveable element of a MEMS sensor 100 . With proper design, the opposite movement of the electrodes than that caused by the external deformation can be achieved. Usual Usually there are at least two different types of materials in the manufacturing process, namely silicon material and oxide material. Although the oxide material is usually etched away at the end of the manufacturing process, leaving only residual oxides of a shape that is difficult to control, there is a certain possibility of creating encapsulated areas with oxide material. These regions represent a "drive" of the bimetallic effect. Such a bimetallic jet represents a holder of an electrode, allowing the electrode to move with temperature and follow external movement.

2 shows in a cross-sectional view (upper figure of 1 ) and in a plan view (bottom figure of 1 ) a greatly simplified operating principle of the proposed offset compensation by means of a second, bimetallic electrode 3. An asymmetrical seismic mass element 5 can be seen. Due to thermal deformation, the substrate (not shown) bends with the first electrode 2, causing a change in capacitance between the first electrode and the second electrode 3 is formed. As a reaction to the thermal bending, the bimetallic electrode 3 arranged in the seismic mass element 5 also bends, as a result of which the cited offset can be compensated for. A gap between the substrate and the seismic mass element 5 becomes larger in the left half of the sensor, but smaller in the right half.

This advantageously results in particular in a micromechanical inertial sensor with improved offset stability and sensing characteristics.

3 shows a perspective view of a in the seismic mass element 5 (not shown) bimetallic electrode 3 of FIG 1 in a higher level of detail, which is arranged within the seismic mass element 5. It can be seen that the metal layer has a bar element 3c, which is held by means of two anchor elements 3d, 3e and has plate-shaped elements 3f...3n that are separated from one another on its underside.

The plate-shaped elements 3f . . . 3n support easy deformability of the second, bimetallic electrode 3, which supports high mobility of the entire seismic mass element 5. The bar element 3c is formed in a first (lower) functional layer 10 made of polysilicon; the oxide materials are formed in upper, thicker functional layers made of polysilicon of the micromechanical inertial sensor 100. FIG.

4 shows a cross section through a first embodiment of the proposed micromechanical inertial sensor 100. One can see a thermal oxide 1a, a first functional layer 10 arranged thereabove and a functional layer 20 arranged thereabove, with blocks of oxide material being arranged in the third functional layer 30, the third Represent electrode 3. These generate a bimetallic effect, so that when the substrate (not shown) bends due to thermal energy previously being heated, the material and thus also the electrodes 2, 3 are deflected heavy side of the asymmetrical rocker are formed.

5 shows an enlarged view of the cross-sectional view of FIG 4 Silicon vias are shown through the second and third functional layers 20, 30, which so to speak enclose the blocks of oxide material.

6 FIG. 1 shows a cross-sectional view through a further embodiment of the proposed micromechanical inertial sensor 100. It can be seen that the two blocks with oxide material are now separated and that there is no substrate underneath the seismic mass element 5. FIG. As a result, an even greater freedom of movement for the electrodes is supported.

7 shows the view from 6 at a higher level of resolution. It can be seen that the two blocks of oxide material are arranged in third functional layer 30 and one block of oxide material is arranged above first functional layer 10 and below second functional layer 20 .

8th shows a cross-sectional view through a further embodiment of the proposed micromechanical inertial sensor 100. It can be seen in this variant that the blocks of oxide material are connected to one another but are separated from one another by at least one cavity 6a...6n. This creates a further design variant for generating the desired bimetallic effect.

9 shows the variant of 8th at a higher level of resolution. It can be seen that the vias between the third functional layer 30 and the second functional layer 20, which enclose the block of oxide material, and through contacts between the second functional layer 20 and the first functional layer 10, which enclose the blocks of oxide material.

As a result, the variants mentioned above 4 until 9 several design opportunities provided to create the desired bimetallic effect.

• - Länge der zweiten, bimetallisch ausgebildeten Elektrode 3
• - Länge des gekapselten Oxid-Materials im Balkenelement 3c
• - Form und Abmessung der Plattenelemente 3f...3n
• - Abstände zwischen den Plattenelementen 3f... 3n
• - Dicke des verkapselten Oxid-Materials

Once it is known or estimated (e.g. by means of simulation or from measurements, e.g. after finalizing the packaging design), a certain TCO compensation can be adjusted with the dimensioning of the structure. An amplitude of the deflection of the bimetallic electrode can be dimensioned by the following parameters, for example:

• - Length of the second bimetallic electrode 3
• - Length of encapsulated oxide material in beam element 3c
• - Shape and dimensions of the plate elements 3f...3n
• - Distances between the plate elements 3f... 3n
• - Thickness of encapsulated oxide material

The parameters mentioned, which are only exemplary, can be implemented in existing designs in a simple manner, as a result of which a large number of micromechanical sensors can be implemented according to the proposed principle.

In the 4 until 9 variants for providing encapsulated oxide regions for an out-of-plane channel are shown. Different variants can advantageously be used to increase the bimetallic effect, with more layers being used to form the bimetallic electrode.

In order to create a bimetallic effect in the MEMS structure, not only the silicon and oxide material can be used, but also metals (e.g. aluminum) and nitrides that can be deposited and patterned.

The proposed compensation principle is advantageously applicable not only to micromechanical out-of-plane inertial sensors, as explained above, but can also be advantageously applied to micromechanical in-plane inertial sensors in which the seismic mass element 5 moves in the plane.

10 shows a top view of such a micromechanical in-plane inertial sensor 100. A seismic mass element 5 can be seen, which can be deflected in the x-direction and detection electrodes with comb-like structures that functionally interact with comb-like structures of the seismic mass element 5 and thereby the deflection of the seismic Capture and evaluate mass element 5.

This represents a capacitance change unit with the bimetallic electrode next to a lateral core, so that a capacitance change due to thermal deformation can also be compensated for in this case by the second bimetallic electrode 3 .

11 shows in principle a sequence of a method for producing a proposed micromechanical inertial sensor 100.

In a step 200, a substrate 1 with a first electrode 2 is provided.

In a step 210, a seismic mass element 5 is provided, with a second, bimetallic electrode 3 being arranged inside the seismic mass element 5. FIG.

Although the invention has been described above on the basis of specific exemplary embodiments, the person skilled in the art can also implement embodiments that are not disclosed or only partially disclosed without departing from the core of the invention.

Claims (10)

Micromechanical inertial sensor (100), comprising: - a substrate with a first electrode (2); and - a seismic mass element (5), characterized in that a second electrode (3) is arranged within the seismic mass element (5), the second electrode (3) being bimetallic. Micromechanical inertial sensor (100) according to claim 1 , characterized in that the second electrode (3) has oxide material enclosed in silicon material. Micromechanical inertial sensor (100) according to claim 1 , characterized in that the second electrode (3) has at least one metal, in particular aluminum and/or nitride. Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second electrode (3) is designed as a bar element (3c) which has plate-shaped, spaced-apart elements (3f...3n) on its underside. Micromechanical inertial sensor (100) according to claim 4 , characterized in that the first electrode is formed in a first functional layer (10) layer. Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second electrode (3) has at least a single block of oxide material. Micromechanical inertial sensor (100) according to one of the preceding claims, characterized in that the second electrode (3) has at least two blocks of oxide material. Micromechanical inertial sensor (100) according to 7, characterized in that at least one cavity (6a...6n) is formed between the at least two blocks of oxide material. Micromechanical inertial sensor (100) according to 8, characterized in that the inertial sensor (100) is an in-plane sensor or an out-of-plane sensor. Method for producing a micromechanical inertial sensor (100), comprising the steps: - Providing a substrate (1) with a first electrode (2); and - Providing a seismic mass element (5), a second bimetallic electrode (3) being arranged within the seismic mass element (5).

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