CN116639644A - Thermoelectric cooling substrate structure and manufacturing method for MEMS inertial sensor - Google Patents

Abstract

The invention discloses a thermoelectric refrigeration substrate structure for an MEMS inertial sensor and a manufacturing method thereof. The in-plane thermoelectric refrigerating element is divided into two modes of heating and refrigerating according to different current directions, so that the room temperature working point setting of the constant temperature control system is realized. Compared with a single heating mode, the power consumption of the temperature control system is reduced, and the quality factor of the MEMS inertial sensor is improved. The embedded glass ring is positioned between the hot end and the cold end of the thermoelectric refrigerating element, so that the heating and cooling efficiency of the thermoelectric refrigerating element is effectively improved, and the deep groove at the back of the substrate inhibits heat transfer between the glass ring inner structure and the environment through the packaging tube shell, so that the heating and cooling efficiency is further improved.

Description

Thermoelectric cooling substrate structure and manufacturing method for MEMS inertial sensor

technical field

The invention belongs to the field of constant temperature control of MEMS inertial sensors, in particular to a structure of a thermoelectric refrigeration substrate and a manufacturing method thereof.

Background technique

With the rapid development of information and integrated circuits in the Internet of Things, MEMS sensors are becoming more and more important as the core components to help achieve perception. MEMS inertial sensors based on micromachining have the advantages of small size, low cost, good consistency, and compatibility with CMOS. They are widely used in consumer electronics, industrial manufacturing, and inertial navigation. The output signal drift caused by ambient temperature changes can seriously damage the measurement accuracy of inertial sensors. The measurement accuracy can be improved to a certain extent through circuit or algorithm compensation, but the problem of temperature drift still exists. Introducing a constant temperature heating structure into the sensor system can isolate the influence of the external environment temperature change on the sensor from the source, and solve the problem of temperature drift. However, this solution does not have an active cooling approach, and the set constant temperature point is required to be higher than the normal operating ambient temperature range, which increases the power consumption of the system. Second, higher temperatures in the sealed cavity of the device lead to increased damping and a lower quality factor. The temperature control system with both heating and cooling functions can set the constant temperature operating point at about 20°C. When the device temperature is lower than the set temperature point, the temperature control system works in heating mode. When the device temperature is higher than the set temperature point, the temperature control system works in cooling mode. This mode greatly reduces the power consumption of the temperature control system, making it possible to apply it in low-power consumption and high-precision requirements scenarios. The core of the heating and cooling dual-mode temperature control system is the thermoelectric cooling element structure based on the Peltier effect, and the commercial vertical structure of the Peltier cooling element is large in size and high in power consumption, which is difficult to integrate into the MEMS inertial sensor. Therefore, it is an urgent problem to realize the constant temperature control of the heating-cooling dual mode in the wafer-level packaging of the MEMS inertial sensor.

Contents of the invention

The technical problem to be solved by the present invention is the problem of high power consumption and low quality factor in the constant temperature control of the inertial sensor. For this reason, a thermoelectric cooling substrate structure with dual heating and cooling modes and its manufacturing method are proposed, which not only realizes the inertial sensor. The constant temperature control reduces the power consumption of the temperature control system and avoids the reduction of the quality factor caused by the high working temperature point.

The technical solution that realizes the object of the present invention is:

A thermoelectric cooling substrate for MEMS inertial sensors, including a substrate, an embedded glass ring, and a thermoelectric cooling element;

The thermoelectric cooling substrate is bonded with the silicon resonant structure and the packaging cap to form a complete MEMS inertial sensor, which are the thermoelectric cooling substrate, the silicon resonant structure and the packaging cap from bottom to top, and the central axes of the three coincide;

Both the front and the back of the thermoelectric cooling substrate are provided with grooves, and the area of the front groove is larger than the area of the movable structure in the silicon resonant structure; the back groove is used to suppress the transfer of heat between the chip and the package shell;

The substrate is provided with an embedded glass ring, which is symmetrical to the center of the substrate, and is used to suppress the lateral heat conduction to the edge of the substrate; the thermoelectric cooling element includes a plurality of N-type resistance strips and a plurality of P-type resistance strips , N-type resistance strips and P-type resistance strips are distributed alternately in parallel and at equal intervals, and the ends are connected end to end by metal wires to form a complete thermoelectric cooling element; and the two ends of the length direction of the resistance strips are located on the inner and outer sides of the embedded glass ring .

A method for manufacturing a thermoelectric refrigeration substrate for MEMS inertial sensors, the specific steps are as follows:

Step 1, etching: etching the silicon substrate to form grooves on the surface of the silicon substrate;

Step 2, bonding: clean the glass substrate and the etched silicon substrate surface, and bond the glass substrate and substrate surface grooves together;

Step 3, glass reflow: place the bonded structure in a high-temperature furnace to turn the glass substrate into a molten state, and the molten glass fills the groove microcavity of the substrate under the action of pressure difference, when the substrate After the groove microcavity is fully filled with molten glass, it is gradually cooled to room temperature, and the glass is re-solidified to form a silicon-glass composite substrate;

Step 4, thinning and polishing: thinning the glass surface and the silicon surface of the silicon-glass composite substrate respectively until the glass surface exposes the substrate and the substrate surface exposes the annular glass, and then polishes;

Step 5, processing thermoelectric cooling elements: depositing N-type thermoelectric materials and P-type thermoelectric materials on the same side of the silicon-glass composite substrate to form N-type resistance strips and P-type resistance strips;

Step 6, processing metal wires: depositing metal on the side of the silicon-glass composite substrate processed with thermoelectric cooling elements to form metal wires;

Step 7, etching shallow grooves on the front side: performing photolithography on the side of the silicon-glass composite substrate processed with thermoelectric cooling elements, and etching to form the front grooves of the substrate;

Step 8, etching deep grooves on the backside: performing photolithography on the side of the silicon-glass composite substrate that is not processed with thermoelectric cooling elements, and etching to form the backside grooves of the substrate.

Compared with the prior art, the present invention has the remarkable advantages of:

1) Constant temperature control avoids structural stress changes caused by environmental temperature changes and improves the measurement accuracy of MEMS inertial sensors; 2) MEMS in-plane thermoelectric cooling elements have two operating modes of heating and cooling, and the operating temperature point of the constant temperature system can be set Compared with the constant temperature system with single heating mode, the power consumption of the control system is greatly reduced; 3) The MEMS in-plane thermoelectric cooling element has two working modes of heating and cooling, which is lower than that of the constant temperature system with single heating mode. The operating temperature point reduces damping within the package, improving the device figure of merit.

Description of drawings

Fig. 1 is the sectional view of the central axis position of the overall structure of the present invention;

Fig. 2 is the top view of Fig. 1;

Fig. 3 is a manufacturing flow chart of the present invention.

Among them: 100. Silicon substrate; 110. Embedded glass ring; 121. N-type resistance strip of thermoelectric cooling element; 122. P-type resistance strip of thermoelectric cooling element; 123. Metal wire of thermoelectric cooling element; 130. Front shallow groove ; 140. Backside deep groove; 200. Silicon resonant structure; 300. Package cap.

Detailed ways

The present invention will be further introduced below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figures 1 and 2, a thermoelectric cooling substrate structure for MEMS inertial sensors in this embodiment includes a silicon substrate 100, an embedded glass ring 110, an N-type resistance strip 121 of a thermoelectric cooling element, and a thermoelectric cooling element. P-type resistance strip 122, metal wire 123 of thermoelectric cooling element. The substrate is bonded with the silicon resonant structure 200 and the packaging cap 300 to form a complete MEMS inertial sensor.

The MEMS inertial sensor structure includes a silicon substrate 100 , a silicon resonant structure 200 and a packaging cap 300 from bottom to top, and the central axes of the three coincide. In the proposed substrate structure, the area of the front shallow groove 130 is larger than the area of the movable structure in the silicon resonant structure 200 , and the area of the back deep groove 140 is the area surrounded by the inner glass ring 110 . The embedded glass ring 110 is symmetrical about the center of the silicon substrate 100 , and its shape can be any symmetrical polygon or a circle. The in-plane width of the embedded glass ring 110 can be optimally adjusted, but is smaller than the lengths of the N-type resistance strips 121 of the thermoelectric cooling element and the P-type resistance strips 122 of the thermoelectric cooling element. The N-type resistance strips 121 of the thermoelectric cooling element and the P-type resistance strips 122 of the thermoelectric cooling element are distributed alternately in parallel and at equal intervals. The length direction of the resistance strips is perpendicular to the side length direction of the embedded glass ring 110 at the corresponding position. The length direction of the resistance strips The two ends are located on the inner and outer sides of the embedded glass ring 110 . The N-type resistance strip 121 of the thermoelectric cooling element and the end of the P-type resistance strip 122 of the thermoelectric cooling element are connected end-to-end through the metal wire 123 of the thermoelectric cooling element to form a complete thermoelectric cooling element.

When the temperature of the silicon resonant structure 200 is higher than the operating temperature point set by the constant temperature control system, it is necessary to cool down the MEMS inertial sensor. At this time, the current direction inside the embedded glass ring 110 is from the P-type resistance strip 122 of the thermoelectric cooling element to the N-type resistance strip 121 of the thermoelectric cooling element, and the electrons move from a low energy level to a high energy level to absorb heat. The back deep groove 140 inhibits the longitudinal heat conduction to the package shell, and the embedded glass ring 110 inhibits the lateral heat conduction to the edge of the silicon substrate 100 , resulting in a lower temperature of the silicon resonant structure 200 . The current direction outside the embedded glass ring 110 is from the N-type resistance strip 121 of the thermoelectric cooling element to the P-type resistance strip 122 of the thermoelectric cooling element, and the electrons move from a high energy level to a low energy level to release heat. The heat is transferred longitudinally through the silicon substrate 100 to the package package and dissipated in the environment. When the temperature of the silicon resonant structure 200 is lower than the operating temperature point set by the constant temperature control system, it is only necessary to change the current direction of the thermoelectric cooling element to realize the temperature rise treatment of the MEMS inertial sensor.

A kind of thermoelectric cooling substrate for MEMS inertial sensor, its manufacturing method, the steps are as follows:

Step 1, deep silicon etching: the silicon wafer is used as the substrate, and the silicon substrate is subjected to deep silicon etching to form grooves on the surface of the silicon substrate; as shown in Figure 3(a).

Step 2, bonding: clean the surface of the glass substrate and the etched silicon substrate, and bond the glass substrate and the grooved side of the silicon substrate together by anodic bonding; as shown in Figure 3(b).

Step 3, glass reflow: place the bonded structure in a high-temperature furnace. Under high temperature conditions (700°C-900°C), the glass substrate becomes molten. Since the microcavity pressure of the silicon substrate is much lower than atmospheric pressure, the Under the action of the pressure difference, the molten glass fills the microcavity of the silicon substrate. When the microcavity of the silicon substrate is completely filled with the molten glass, it is gradually cooled to room temperature, and the glass is re-solidified to form a silicon-glass composite substrate; as shown in the figure 3(c).

Step 4, Thinning and polishing: Thinning the glass surface and the silicon surface of the silicon-glass composite substrate respectively, until the glass surface exposes the silicon, and the silicon surface exposes the annular glass, and then polishes to ensure that the surface flatness and roughness are at Within the tolerance range of the subsequent process; as shown in Figure 3(d).

Step 5, processing thermoelectric cooling elements: Deposit N-type thermoelectric materials and P-type thermoelectric materials on the same side of the silicon-glass composite substrate by sputtering or evaporation, and then remove excess materials through etching or stripping processes, N-type resistance strips and P-type resistance strips are formed; as shown in Figure 3(e). The N-type resistors and P-type resistors can be Bi ₂ Te ₃ alloys, or other thermoelectric refrigeration materials compatible with MEMS technology.

Step 6, processing metal wires: Spin-coat photoresist on the side of the silicon-glass composite substrate processed with thermoelectric cooling elements, expose and deposit metal Au, and remove excess Au by lift-off process; as shown in Figure 3(f).

Step 7, etching shallow grooves on the front side: perform photolithography on the side of the silicon-glass composite substrate processed with thermoelectric cooling elements, and use photoresist as a mask to form shallow grooves on the front side of the substrate by reactive ion etching; as shown in Figure 3 ( g).

Step 8, etch deep grooves on the back side: perform photolithography on the side of the silicon-glass composite substrate that is not processed with thermoelectric cooling elements, and use photoresist as a mask to form deep grooves on the back side of the substrate by deep reactive ion etching. As shown in Figure 3(h).

The above is the manufacturing process of the thermoelectric cooling substrate of the present invention.

Claims (8)

1. The thermoelectric refrigeration substrate for the MEMS inertial sensor is characterized by comprising a substrate, an embedded glass ring and a thermoelectric refrigeration element;

the thermoelectric refrigeration substrate, the silicon resonant structure and the packaging cap are bonded to form a complete MEMS inertial sensor, and the thermoelectric refrigeration substrate, the silicon resonant structure and the packaging cap are respectively arranged from bottom to top, and the central axes of the thermoelectric refrigeration substrate, the silicon resonant structure and the packaging cap are coincident;

grooves are formed in the front surface and the back surface of the thermoelectric refrigeration substrate, and the area of the groove in the front surface is larger than that of a movable structure in the silicon resonance structure; the back side groove is used for inhibiting heat transfer between the chip and the packaging tube shell;

the substrate is provided with an embedded glass ring which is symmetrical about the center of the substrate and used for inhibiting transverse heat conduction to the edge of the substrate; the thermoelectric refrigerating element comprises a plurality of N-type resistor strips and a plurality of P-type resistor strips, wherein the N-type resistor strips and the P-type resistor strips are alternately distributed in parallel at equal intervals, and the ends of the N-type resistor strips and the P-type resistor strips are connected end to end through metal wires to form a complete thermoelectric refrigerating element; and the two ends of the resistor strip in the length direction are positioned at the inner side and the outer side of the embedded glass ring.

2. The thermoelectric cooling substrate for a MEMS inertial sensor of claim 1, wherein the in-plane width of the embedded glass ring 110 is adjustable and less than the length of the N-type resistive strips of the thermoelectric cooling elements and the P-type resistive strips of the thermoelectric cooling elements.

3. The thermoelectric cooling substrate for MEMS inertial sensor according to claim 1, wherein the N-type resistive strips of the thermoelectric cooling element and the P-type resistive strips of the thermoelectric cooling element are perpendicular to the side length of the embedded glass ring at the corresponding positions.

4. The thermoelectric cooling substrate for a MEMS inertial sensor of claim 1, wherein the area of the backside groove is the area enclosed inside the embedded glass ring.

5. The thermoelectric cooling substrate for MEMS inertial sensor of claim 1, wherein when the temperature of the silicon resonant structure is higher than the operating temperature point set by the thermostatic control system, the direction of current inside the embedded glass ring is from the P-type resistive strip of the thermoelectric cooling element to the N-type resistive strip of the thermoelectric cooling element; the current direction outside the embedded glass ring is from the N-type resistor strip of the thermoelectric refrigerating element to the P-type resistor strip of the thermoelectric refrigerating element; when the temperature of the silicon resonant structure is lower than the working temperature point set by the constant temperature control system, the current direction at the inner side of the embedded glass ring is from the N-type resistance strip of the thermoelectric refrigeration element to the P-type resistance strip of the thermoelectric refrigeration element; the current direction outside the embedded glass ring is from the P-type resistor strip of the thermoelectric cooling element to the N-type resistor strip of the thermoelectric cooling element.

6. The manufacturing method of the thermoelectric refrigeration substrate for the MEMS inertial sensor is characterized by comprising the following specific steps of:

step 1, etching: etching the silicon substrate to form a groove on the surface of the silicon substrate;

step 2, bonding: cleaning the surfaces of the glass substrate and the etched silicon substrate, and bonding the glass substrate and the grooves on the surfaces of the substrate together;

step 3, glass reflux: placing the bonded structure in a high-temperature furnace, changing the glass substrate into a molten state, filling the molten glass into a groove microcavity of the substrate under the action of pressure difference, gradually cooling to room temperature after the substrate groove microcavity is fully filled with the molten glass, and re-solidifying the glass to form the silicon-glass composite substrate;

step 4, thinning and polishing: respectively thinning the glass surface and the silicon surface of the silicon-glass composite substrate until the silicon surface is exposed out of the glass surface and the silicon surface is exposed out of the annular glass, and then polishing;

step 5, processing the thermoelectric refrigeration element: depositing an N-type thermoelectric material and a P-type thermoelectric material on the same surface of a silicon-glass composite substrate to form an N-type resistor strip and a P-type resistor strip;

step 6, processing metal wires: depositing metal on one surface of the silicon-glass composite substrate, which is processed with the thermoelectric refrigerating element, to form a metal wire;

step 7, etching shallow grooves on the front surface: photoetching one side of the silicon-glass composite substrate, on which the thermoelectric refrigerating element is processed, and etching to form a front groove of the substrate;

step 8, back etching deep grooves: and photoetching the surface of the silicon-glass composite substrate, on which the thermoelectric refrigerating element is not processed, and etching to form a back groove of the base plate.

7. The method of claim 6, wherein the N-type and P-type resistors in step 5 are materials having thermoelectric cooling properties and compatible with MEMS processing.

8. The method for manufacturing a thermoelectric refrigeration substrate for a MEMS inertial sensor according to claim 7, wherein the material is Bi ₂ Te ₃ 。