Semiconductor chip and gas sensor comprising such semiconductor chip

Abstract

The invention relates to a semiconductor chip (100) for determining the thermal conductivity, the thermal diffusivity, the specific heat capacity of a gas mixture and, as a secondary determination, the density and / or the viscosity of a gas mixture, comprising: a main body (110); a cantilever cavity (120) enclosed by the main body; an oscillator cantilever (130) protruding into the cantilever cavity (120) and a piezoelectric exciter (131, 132, 133) for exciting vibrations; at least one heater cantilever (140) protruding into the cantilever cavity (120); a heating element (144) in a cantilever end portion (142); and a temperature sensor element (154, 164); wherein a portion of the cantilever cavity (120) extends between the heating element (144) and the temperature sensor element (154, 164), and wherein at least a portion of the cantilever cavity (120) extends between the heater cantilever (140) and the oscillator cantilever (130); wherein the main body (110) further has a main body stiffener (112) extending between an oscillator region (123) and a heater region (124) of the cantilever cavity (120), wherein the oscillator cantilever (130) is arranged in the oscillator region (123) and the heater cantilever (140) is arranged in the heater region (124).

Description

Technical Field

[0001] The present invention relates to semiconductor chips and gas sensors including such semiconductor chips, particularly semiconductor chips for first determining the thermal conductivity, thermal diffusivity and / or specific heat capacity of a gas mixture and secondly determining the density and / or viscosity of the gas mixture. Background Technology

[0002] Semiconductor chips and gas sensors of the discussed type are disclosed in publication WO 2022 / 008 212 A1. The semiconductor chip described therein includes: a body; a cantilever cavity surrounded by the body; at least one oscillator cantilever projecting from the body into the cantilever cavity and including at least one piezoelectric actuator for exciting the cantilever to vibrate; at least one heater cantilever projecting from the body into the cantilever cavity and having a heating element in a cantilever end portion opposite to the body; at least one first temperature sensor element, wherein at least a portion of the cantilever cavity extends between the heating element and the first temperature sensor element; and wherein at least a portion of the cantilever cavity extends between the heater cantilever and the oscillator cantilever.

[0003] Studies related to this invention have shown that the gas density in the environment of the oscillator cantilever exhibits a gradient due to thermal measurements. This can impair the accuracy of density or viscosity measurements. To remedy this, an alternating measurement mode for determining the thermal measurement variable and for measurement using the oscillator cantilever can be considered; however, this significantly increases the time required for the measurement cycle. Therefore, the object of this invention is to find a remedy. Summary of the Invention

[0004] The semiconductor chip according to the invention is used to first determine the thermal conductivity, thermal diffusivity, and / or specific heat capacity of a gas mixture, and secondly to determine the density and / or viscosity of the gas mixture, and the semiconductor chip comprises: a body; a cantilever cavity surrounded by the body; at least one oscillator cantilever protruding from the body into the cantilever cavity and including at least one piezoelectric actuator for exciting the cantilever to vibrate; at least one heater cantilever protruding from the body into the cantilever cavity and having a heating element in a cantilever end portion opposite to the body; at least one first temperature sensor element, wherein at least a portion of the cantilever cavity extends between the heating element and the first temperature sensor element; and wherein at least a portion of the cantilever cavity extends between the heater cantilever and the oscillator cantilever; wherein, according to the invention, the body further includes a body bridge extending between an oscillator region and a heater region of the cantilever cavity, wherein the oscillator cantilever is arranged in the oscillator region and the heater cantilever is arranged in the heater region.

[0005] The semiconductor chip according to the invention has at least one means for detecting the temperature of the heater cantilever. In its simplest form, the heating element is such a means, wherein the temperature of the heater cantilever is determined based on a measured value of the resistance of the heating element. Alternatively, the heater cantilever may have a separate sensor element for temperature measurement.

[0006] In a further development of the invention, the semiconductor chip includes at least one sensor cantilever protruding from the body into the cantilever cavity, and includes a first temperature sensor element in the cantilever end portion away from the body, wherein the sensor cantilever is arranged in the heater region.

[0007] In a further development of the invention, the oscillator cantilever includes a second temperature sensor element, particularly in the cantilever end portion of the oscillator cantilever that is away from the body.

[0008] In a further development of the invention, the oscillator cantilever and the heater cantilever are spaced apart by not less than 500 μm, for example not less than 800 μm; and / or the oscillator cantilever and the heater cantilever are spaced apart by not more than 2000 μm, for example not more than 1500 μm.

[0009] In a further development of the invention, the oscillator cantilever has a thickness of not less than 3 μm, particularly not more than 20 μm, and / or the oscillator cantilever has a length of not less than 400 μm, and / or the oscillator cantilever has a length of not more than 1000 μm, particularly not more than 750 μm.

[0010] In a further development of the invention, the chip comprises silicon, particularly polycrystalline silicon.

[0011] In a further development of the invention, the semiconductor chip further includes a hydrogen-impermeable coating, which in particular includes Al2O3 or ALN, especially for protecting the metal conductor tracks formed on the surface segments of the body or cantilever, such that the coating specifically covers the conductor tracks.

[0012] In a further development of the invention, the heater cantilever has thermal resistance such that, under reference conditions in a carbon dioxide atmosphere, the temperature difference between the cantilever end of the heater cantilever and the end of the cantilever on the main body side is not less than 5 K / mW per unit heating power, and particularly not less than 6 K / mW.

[0013] In a further development of the invention, each cantilever has its own longitudinal direction of extension, wherein each cantilever has a transverse direction perpendicular to its longitudinal direction in a plane of the cantilever surface, wherein the heater cantilever has a greater width in the transverse direction in its end portion where the heating element is arranged than in its base portion facing the body, wherein in particular, the heating element has a greater width in the transverse direction than in its base portion facing the body, wherein the width of the end portion of the cantilever is, for example, at least one and a half times the width of the base portion facing the body, particularly at least 1.9 times.

[0014] In a further development of the present invention, the first temperature sensor element is positioned at a distance of not less than 50 μm from the heating element, and / or the first temperature sensor element is positioned at a distance of not more than 200 μm from the heating element.

[0015] In a further development of the invention, the body has a substantially polygonal profile surrounding the cantilever cavity, wherein at least one sensor cantilever and a heater cantilever protrude from the body, from different sides of the polygonal profile, and particularly from opposite sides of the polygonal profile into the cantilever cavity.

[0016] In a further development of the invention, the semiconductor chip further includes at least one cover covering the cantilever cavity. In one embodiment of this further development, the cover has a cover surface facing the cantilever cavity and at least one protrusion projecting from the cover surface in the direction of the body bridge.

[0017] In a further development of the invention, the orthogonal projection of the protrusion on the plane representing the cover surface overlaps with the orthogonal projection of the main bridge on the same plane by at least 50%, particularly at least 75%, and preferably 100%.

[0018] In a further development of the invention, the distance between the main bridge 112 and the protrusion is no greater than 75% of the distance between the oscillator cantilever and the plane representing the cover surface, and particularly no greater than 50%.

[0019] In a further development of the invention, the cover has a porous material for enabling diffuse gas exchange through the cover.

[0020] A gas sensor for analyzing gases or gas mixtures according to the present invention comprises: a semiconductor chip according to any one of the preceding claims; and a measurement and operation circuit configured to determine the density and viscosity of the gas mixture based on the vibration characteristics of an oscillator cantilever, and to determine the thermal conductivity, thermal diffusivity, and / or specific heat capacity of the gas mixture based on the measured temperature of a temperature sensor element and the power consumption of a heating element. Attached Figure Description

[0021] The invention is described in more detail below with reference to the exemplary embodiments shown in the accompanying drawings.

[0022] In the attached diagram: Figure 1 A top view of an exemplary embodiment of a semiconductor chip according to the present invention in the plane of a cantilever is shown; Figure 2 An exemplary embodiment of the semiconductor chip according to the present invention is shown along... Figure 1 A cross-sectional view of line (II-II) in the middle; Figure 3 Showing from Figure 1 and Figure 2 A detailed top view of a portion of the oscillator region of the cantilever cavity and an adjacent region of the main body, according to an exemplary embodiment of the semiconductor chip of the present invention; and Figure 4 Showing from Figures 1 to 3 Details of the heater cantilever in an exemplary embodiment; and Figure 5 A schematic diagram of the layer structure of an exemplary embodiment of a semiconductor chip is shown. Detailed Implementation

[0023] Figures 1 to 4 An exemplary embodiment of the semiconductor chip 100 shown according to the present invention includes a body 110, which in particular comprises polycrystalline silicon. Compared with monocrystalline silicon, polycrystalline silicon has a lower thermal conductivity, resulting in lower heat loss in the heating element.

[0024] The main body 110 surrounds the cantilever cavity 120, which is divided by the main body bridge 112 into an oscillator region 123 and a heater region 124. The area of ​​the heater region 124 is approximately 0.5 mm². 2 It is approximately twice the area of ​​the oscillator region 123. The oscillator cantilever 130 extends into the oscillator region 123 with a length of approximately half a millimeter and a width of approximately one-tenth of a millimeter. The oscillator cantilever 130 has a temperature sensor element 134 in its cantilever end portion, which—as Figure 3 As shown—specifically including Pt resistive elements. The oscillator cantilever 130 further includes piezoelectric transducers 131, 132, 133 for exciting or detecting the vibration of the oscillator cantilever 130. The piezoelectric transducer may, for example, include AlN, particularly Sc-doped AlN.

[0025] The thickness of the oscillator cantilever 130 is, for example, about 5 μm. This thickness is well-suited for gas pressures up to several MPa. For higher gas pressures, a greater material thickness should be considered. For example, for a gas pressure of 100 MPa, a material thickness of about 10 μm is advantageous.

[0026] In a heater region 124, spatially separated from the oscillator region 123, a heater cantilever 140 is arranged, protruding from the body 110 into the cantilever cavity 120 by approximately half a millimeter in length. The heater cantilever 140 has a heating element 144 in its cantilever end portion 142, which specifically comprises, for example, a serpentine resistive structure made of Pt. The cantilever end portion 142 with the heating element 144 has a width B of approximately one-tenth of a millimeter and a length L of approximately one-tenth to one-sixth of a millimeter, wherein the heater cantilever 140 has a base portion 146 between the cantilever end portion and the body, the base portion 146 having a width of only approximately one-twentieth of a millimeter. This reduced width of the base portion 146 compared to the cantilever end portion has the effect of increasing the thermal resistance of the heater cantilever. As a result, at a given heating power, a larger temperature difference can be achieved compared to the environment of the heating element 144. For example, a temperature difference of approximately 62 K was achieved with a heating power of 3 mW in a carbon dioxide environment, while a design where the heater cantilever 140 has a full width of one-tenth of a millimeter achieved only approximately 37 K at the same heating power. Using polycrystalline silicon as the material for the semiconductor chip 100 also helps to achieve a sufficiently large temperature difference because polycrystalline silicon has a lower thermal conductivity than monocrystalline silicon. The heater cantilever 140 further includes a temperature sensor element 148 in its cantilever end portion 142 for detecting the temperature of the cantilever end portion. This temperature sensor element 142 specifically includes a Pt resistive element. In principle, the temperature can also be determined based on the resistance value of the heating element; however, independent temperature measurement using the additional temperature sensor element 148 is more accurate.

[0027] Two sensor cantilevers 150 and 160, laterally spaced from heater cantilevers 140, protrude into the heater region 124 of cantilevers 120. On one hand, sensor cantilevers 150 and 160, and on the other hand, heater cantilevers 140, are connected to the body 110 on opposite sides of the opening in the heater region 124 within the body 110, in order to thermally decouple heater cantilevers 140 from sensor cantilevers 150 and 160 as much as possible. Each of the sensor cantilevers 150 and 160 has a temperature sensor element 154 and 164 in its cantilever end portion, which specifically includes a Pt resistive element having a structure similar to the resistive element 134 on the oscillator cantilevers 130. The temperature sensor elements 154 and 164 are arranged at different distances from the heating element, ranging from about one-twentieth of a millimeter to about one-third of a millimeter, with one of the sensor elements being no more than one-fifth of a millimeter from the heating element. By arranging the sensor elements at different distances, the measurement range for the thermal conductivity of the surrounding gas mixture is increased compared to an arrangement with only one sensor element.

[0028] The oscillator cantilever 130 is spaced approximately 1200 μm from the heater cantilever 140 to minimize the temperature gradient along the oscillator cantilever caused by the heating element. The body bridge 112 also helps to reduce the temperature gradient by forming a thermal bridge that extends parallel to the oscillator cantilever 130.

[0029] Therefore, when the heating element is heated to 62K, the temperature fluctuation along the oscillator cantilever 130 is no greater than 0.02K.

[0030] The semiconductor chip 100 further includes a cover 180 covering the cantilever cavity 120. This cover specifically comprises a porous material through which gas exchange can occur. For example, the pore size can be approximately 1 μm. Suitable materials include sintered bronze, silicon, ceramics, and polymers. The wall thickness of the cover 180 is approximately 0.5 to 0.8 mm.

[0031] In the exemplary embodiment shown here, a protrusion 184 having a prismatic cross-section protrudes from the end face 182 of the cover opposite to the cantilever cavity 120, the protrusion extending parallel to the main bridge 112. This protrusion 184 serves as a thermal bridge and, thus together with the main bridge, helps to homogenize the temperature in the oscillator region 123.

[0032] The main body 110 may have a first main body-side temperature sensor element 174 adjacent to the oscillator region 123 of the cantilever cavity 120, which also includes a Pt resistive element. However, this is entirely optional and can be used, for example, to detect a temperature gradient over the oscillator region, for example, by comparing its measured temperature with the measured temperature of the temperature sensor element 134 of the oscillator cantilever 130. An optional second main body-side temperature sensor element 172, having a similar structure to the first main body-side temperature sensor element 174, may be formed on the main body bridge 112. The second main body-side temperature sensor element 172 on the main body bridge 112 can be used together with the first main body-side temperature sensor element to monitor the temperature uniformity in the oscillator region 123.

[0033] The piezoelectric electrodes 131, 132, 133 and the resistive elements of the temperature sensor elements 134, 148, 174, as well as the heater 144, are both connected to the measurement and operation circuit via a metal conductor track 180 formed on the surface 126 of the body 110.

[0034] Semiconductor chip 100 has a layer structure, which references Figure 5The oscillator cantilever 130 shown is briefly explained. The layer structure initially comprises a first silicon dioxide layer 24 on a substrate body 22 made of silicon. A polycrystalline silicon layer 26 with a thickness of approximately 5 μm is formed on the first silicon dioxide layer 24. The cantilever 130 is formed within this polycrystalline silicon layer 26. Following the polycrystalline silicon layer 26 is a second silicon dioxide layer 28. An adhesion layer 30 is further provided, on which a first platinum structure 32 is formed. This first platinum structure 32 includes, on one hand, the resistive element of the temperature sensor element 134 and an optional heater 136 on the oscillator cantilever 130, and on the other hand, electrodes for piezoelectric transducers 131, 132, and 133. Suitable materials for the adhesion layer 30 include, in particular, Ti, as well as AlN and Al2O3, the latter being preferred due to its better compatibility with hydrogen. Following platinum structure 32 are AlN layer 34 for forming piezoelectric transducers 131, 132, and 133, and a second platinum structure 36, which includes electrodes for the piezoelectric transducers and an optional heater 136 for the oscillator cantilever 130. The conductor tracks, electrodes of piezoelectric transducers 131, 132, and 133, and PT resistor elements are covered with a protective layer 38, which comprises, for example, AlN or Al₂O₃ and is particularly resistant to hydrogen permeation. This layer structure is correspondingly configured in the other cantilever beams.

Claims

1. A semiconductor chip (100) for first determining the thermal conductivity, thermal diffusivity, and / or specific heat capacity of a gas mixture and secondly determining the density and / or viscosity of the gas mixture, comprising: Main body (110); A cantilever cavity (120) is surrounded by the main body; At least one oscillator cantilever (130) and at least one piezoelectric actuator (131, 132, 133), the at least one oscillator cantilever (130) protruding from the body (110) into the cantilever cavity (120), the at least one piezoelectric actuator (131, 132, 133) being used to excite the cantilever to vibrate; At least one heater cantilever (140) protrudes from the body (110) into the cantilever cavity (120) and has a heating element (144) in the cantilever end portion (142) opposite to the body (110); At least one first temperature sensor element (154, 164); At least a portion of the cantilever cavity (120) extends between the heating element (144) and the first temperature sensor elements (154, 164); and At least a portion of the cantilever cavity (120) extends between the heater cantilever (140) and the oscillator cantilever (130); Its features are, The main body (110) further includes a main body bridge (112) extending between the oscillator region (123) and the heater region (124) of the cantilever cavity (120), wherein the oscillator cantilever (130) is arranged in the oscillator region (123) and the heater cantilever (140) is arranged in the heater region (124).

2. The semiconductor chip of claim 1, further comprising at least one sensor cantilever projecting from the main body into the cantilever cavity and comprising the first temperature sensor element in a cantilever end portion facing away from the main body, wherein, The sensor cantilever is arranged in the heater area.

3. The semiconductor chip according to any one of the preceding claims, wherein The oscillator cantilever includes a second temperature sensor element, particularly in the cantilever end portion of the oscillator cantilever that is away from the body.

4. The semiconductor chip according to any one of the preceding claims, wherein The oscillator cantilever is spaced from the heater cantilever by not less than 500 μm, for example, not less than 800 μm; and / or wherein the oscillator cantilever is spaced from the heater cantilever by not more than 2000 μm, for example, not more than 1500 μm.

5. The semiconductor chip according to any one of the preceding claims, wherein The oscillator cantilever has a thickness of not less than 3 μm, and particularly not more than 20 μm, and / or Wherein, the oscillator cantilever has a length of not less than 400 μm, and / or The oscillator cantilever has a length of no more than 1000 μm, and particularly no more than 750 μm.

6. The semiconductor chip according to any one of the preceding claims, wherein The chip comprises silicon, particularly polycrystalline silicon.

7. The method according to any one of the preceding claims, further comprising: Hydrogen-impermeable coatings, particularly comprising Al2O3 or ALN, are used to protect metal conductor tracks formed on surface sections of the body or the cantilever.

8. The semiconductor chip according to any one of the preceding claims, wherein The heater cantilever has thermal resistance such that, under reference conditions in a carbon dioxide atmosphere, the temperature difference between the cantilever end of the heater cantilever and the end of the cantilever on the main body side is not less than 5 K / mW per unit heating power, and particularly not less than 6 K / mW.

9. The semiconductor chip according to any one of the preceding claims, wherein Each of the cantilever beams has its own longitudinal direction of extension, and in the longitudinal direction, each of the cantilever beams has a transverse direction perpendicular to its longitudinal direction in the plane of the surface of the cantilever beam, wherein the heater cantilever has a greater width in the transverse direction in its cantilever end portion where the heating element is arranged than in its base portion facing the body, wherein, in particular, the heating element has a greater width in the transverse direction than in its base portion facing the body, wherein the width of the cantilever end portion is, for example, at least one and a half times the width of the base portion facing the body, particularly at least 1.9 times.

10. The semiconductor chip according to any one of the preceding claims, wherein The first temperature sensor element is positioned at a distance of not less than 50 μm from the heating element, and / or The first temperature sensor element is positioned at a distance of no more than 200 μm from the heating element.

11. The semiconductor chip according to claim 2 or any one of the preceding claims depending on claim 2, wherein The body has a substantially polygonal profile surrounding the cantilever cavity, wherein the at least one sensor cantilever and the heater cantilever protrude from the body, from different sides of the polygonal profile, and particularly from opposite sides of the polygonal profile into the cantilever cavity.

12. The semiconductor chip according to any of the preceding claims, further comprising: At least one cover covering the cantilever cavity.

13. The semiconductor chip of claim 12, wherein, The cover has a cover surface facing the cantilever cavity and at least one protrusion protruding from the cover surface in the direction of the main bridge.

14. The semiconductor chip of claim 13, wherein, The orthogonal projection of the protrusion on the plane representing the covering surface overlaps with the orthogonal projection of the main bridge on that plane by at least 50%, particularly at least 75%, and preferably 100%.

15. The semiconductor chip of claim 14, wherein, The distance between the main bridge and the protrusion is no greater than 75% of the distance between the oscillator cantilever and the plane representing the covering surface, and in particular no greater than 50%.

16. The semiconductor chip according to claim 12 or a claim dependent thereon, wherein The cover has a porous material for enabling the exchange of diffused gases through the cover.

17. A gas sensor for analyzing a gas or a gas mixture, comprising: Semiconductor chip according to any one of the preceding claims; as well as A measurement and operation circuit is configured to determine the density and viscosity of the gas mixture based on the vibration characteristics of the oscillator cantilever, and to determine the thermal conductivity, thermal diffusivity, and / or specific heat capacity of the gas mixture based on the measured temperature of the temperature sensor element and the power consumption of the heating element.

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