Thermal conductivity sensor comprising cap layer

Abstract

A thermal conductivity sensor for measuring a concentration of a gas, the sensor comprising: a substrate portion; a dielectric layer including a dielectric film, where the dielectric film is provided with a heater; a first gap between the substrate portion and the dielectric film, where the primary dielectric film is over the first primary gap; and a micromachined cap layer; and a second gap between the cap layer and the dielectric film. A method of manufacturing a thermal conductivity sensor is also described.

Description

Technical Field

[0001] The present disclosure relates to a thermal conductivity sensor for measuring the concentration of a gas and a method of manufacturing the thermal conductivity sensor. Background Art

[0002] Thermal conductivity sensors can be used to measure the concentration of a gas. For example, changes in gas concentration can be detected as changes in the resistance of a heater provided in the sensor.

[0003] The sensitivity of the sensor may vary depending on the thermal conductivity of the target gas and the difference in thermal conductivity between the target gas and a reference gas (e.g., air). The sensitivity of the sensor may also depend on the efficiency of heat transfer from the heater through the target gas. In the case where, for example, the value of the thermal conductivity of the target gas is very close to the thermal conductivity of the reference gas, the efficiency of heat transfer from the heater through the target gas may need to be increased to ensure satisfactory sensor sensitivity. Summary of the invention

[0004] A thermal conductivity sensor for measuring the concentration of a gas is described herein. The sensor may include a substrate portion. The sensor may include a dielectric layer including a dielectric film. The dielectric film may be provided with a heater. For example, the thermal conductivity sensor may include a heater in and / or on the dielectric film. The thermal conductivity sensor may include a first gap between the substrate portion and the dielectric film. The dielectric film may be located above the first gap. The sensor may include a cover layer. The sensor may include a second gap located between the cover layer and the dielectric film.

[0005] The cap layer may be a micro-machined cap layer. For example, the cap layer may be formed by surface micro-machining.

[0006] As will be appreciated by those skilled in the art, "micromachining" may include fabricating microstructures on a substrate, and "surface micromachining" may include fabricating microstructures by deposition and patterning of thin films.

[0007] The dielectric film may be suspended such that a first gap exists between the dielectric film and the substrate portion.The dielectric film layer may include one or more openings.

[0008] A portion of the capping layer may be suspended such that a second gap exists between the portion of the capping layer and the dielectric film. For example, the capping layer may be formed on a sacrificial layer between the dielectric film and the capping layer, and the second gap may include a removed (eg, etched) portion of the sacrificial layer.

[0009] The cap layer may provide a pathway for heat to transfer from the heater through the gas to the environment, thus allowing an increase in the percentage of heat transferred through the gas and thus improving the sensitivity of the thermal conductivity sensor.

[0010] In particular, a micromachined cap layer can advantageously allow very precise control of a second gap on the side of the dielectric film opposite the first gap, such that the distance between the dielectric film and the cap layer surface (i.e., the thickness of the second gap) is within the distance of the device thermal boundary layer. In other words, the cap layer can be formed very close to the dielectric film, which can increase the percentage of heat transferred to the cap layer by the gas (e.g., air), thereby further increasing the sensitivity of the sensor. For example, the sensitivity can be increased relative to a cap layer formed by wafer bonding or at the package level.

[0011] As will be appreciated by the skilled person, where the dielectric film and the cap layer surface are within the distance of the device thermal boundary layer, the percentage of heat transferred between the heater and the cap layer surface by the gas in the second gap will increase, thus increasing the proportion of heat transferred by the gas. However, to significantly improve performance, the thickness of the second gap can be much smaller than the thermal boundary layer (e.g., a second gap of 20 μm or less). The effect will be more significant as the distance between the dielectric film and the cap layer decreases, which means that a strictly controlled minimum distance is particularly advantageous.

[0012] The cap layer may be formed in direct contact with the dielectric layer.For example, the cap layer may be micromachined such that a portion of the cap layer is formed around the second gap.

[0013] In some examples, the second gap has a thickness of 20 μm or less.

[0014] The second gap may be configured such that a thickness of the gap in a direction passing through the center of the dielectric film is less than 0.5 times (eg, less than 0.25 times) a width of the dielectric film.

[0015] In some examples, the second gap has a thickness between 0.25 and 4 times the thickness of the dielectric film.

[0016] In some examples, the cap layer has a thickness of 5 μm or less.

[0017] Furthermore, advantageously, a thermal conductivity sensor including a micromachined cover layer may be simpler and more cost-effective to manufacture, for example compared to a sensor having a cover layer formed by wafer bonding or at the packaging level.

[0018] The sensor may include: a substrate portion; an intermediate layer disposed on the substrate portion; and a semiconductor layer disposed on the intermediate layer. For example, the substrate portion may include silicon. The intermediate layer may include a dielectric. The intermediate layer may include an oxide (e.g., silicon dioxide). The semiconductor layer may include silicon.

[0019] In some examples, the substrate portion, the intermediate layer, and the semiconductor layer may be collectively referred to as a “substrate” and / or a “chip.” For example, a sensor may include an SOI chip (e.g., formed from an SOI wafer) that includes a substrate portion (also referred to as a semiconductor substrate portion), an intermediate layer, and a semiconductor layer.

[0020] Collectively, the substrate portion, intermediate layers, and semiconductor layers may be referred to as a "wafer," such as a silicon-on-insulator (SOI) wafer from which several sensors may be formed.

[0021] Advantageously, the thermal conductivity sensor may be manufactured using SOI technology.

[0022] In some examples, the substrate portion includes a semiconductor material such as silicon, silicon carbide, polycrystalline silicon and / or polysilicon carbide. In some examples, the substrate includes an SOI material or an SOI wafer. In some examples, the substrate includes glass. In some examples, the substrate includes sapphire. In some examples, the substrate includes a semi-insulating material, such as semi-insulating silicon carbide. In some examples, the substrate includes a combination of a dielectric material and a semiconductor material.

[0023] The cap layer may include a metal or other thermally conductive material. For example, a metal cap layer may act as a hot plate that leads to a more favorable thermal path from the heater to the environment, further providing a higher sensitivity of the sensor to a given gas. Examples of suitable metals may include complementary metal oxide semiconductor (CMOS) metals, such as aluminum, tungsten, copper, and / or titanium. Examples of other suitable thermally conductive materials may include polysilicon and / or silicon.

[0024] In some examples, the cap layer includes a dielectric material such as silicon nitride and / or silicon oxynitride. Advantageously, the dielectric material may have a low or lower thermal conductivity (e.g., lower than metal), which means that heat transfer through the cap layer is minimized, thereby resulting in reduced power consumption of the thermal conductivity sensor.

[0025] In some examples, the cap layer includes multiple sub-layers, including a metallic sub-layer and / or a dielectric sub-layer.

[0026] In some examples, the thermal conductivity sensor includes a first sacrificial layer between the dielectric film and the substrate portion. The first sacrificial layer may include a first gap. The first gap may be formed by removing (e.g., etching) one or more portions of the first sacrificial layer. The substrate portion and the first sacrificial layer may be collectively referred to as a "substrate" and / or a "chip". For example, the first sacrificial layer may include a dielectric (e.g., oxide, silicon nitride) and / or a semiconductor material (e.g., silicon, polysilicon). For example, the first gap may include an etched portion of a semiconductor layer and / or an insulator layer of a wafer (e.g., an SOI wafer). In some examples, the first sacrificial layer may be between 1 μm and 5 μm thick.

[0027] In some examples, the thermal conductivity sensor includes a second sacrificial layer between the cap layer and the dielectric layer. The second gap may include a removed (e.g., etched) portion of the second sacrificial layer. For example, the second sacrificial material may include a dielectric (e.g., silicon nitride), a polymer (e.g., polyamide), and / or a semiconductor material (e.g., polysilicon). In some examples, the second sacrificial layer may be at most 20 μm thick.

[0028] The thermal conductivity sensor may include a third sacrificial layer. For example, where the first sacrificial layer includes a semiconductor layer of a substrate (e.g., an SOI substrate), the third sacrificial layer may include an insulator layer of the substrate (e.g., an SOI substrate), the insulator layer being disposed on the semiconductor layer. For example, the third sacrificial layer may include an insulator or a dielectric, such as an oxide. The third sacrificial layer may include a buried oxide layer of the SOI substrate. In some examples, the third sacrificial layer may be between 50 nm and 3 μm thick.

[0029] In some examples, the first gap includes a removed (eg, etched) portion of the substrate.

[0030] In some examples, the cover layer includes an opening, referred to as a cover opening. For example, the cover opening can allow the second gap to be in fluid communication with the external atmosphere.

[0031] In some examples, the dielectric film is a main dielectric film, and the thermal conductivity sensor further includes a reference dielectric film provided with a reference heater. The reference dielectric film is located above the reference gap. In addition to the main part as described above, the reference dielectric film, the reference heater, and the reference gap together provide a reference part in the sensor of the present disclosure. The main dielectric film is exposed to the external atmosphere, while the reference dielectric film is provided in a sealed chamber.

[0032] Advantageously, the reference portion of the sensor may allow compensation for any environmental changes, such as temperature changes, which would otherwise affect the gas concentration measurement. The reference portion may also compensate for other influences, such as common mode noise in the supply voltage circuit and any noise common to the primary and reference heaters and / or any additional temperature sensors.

[0033] In some examples, the main dielectric film and the reference dielectric film may be on two different chips (e.g., formed on two different substrates). One chip provided with the reference dielectric film may be in a sealed package, while the main dielectric film on the other chip may be exposed to the external atmosphere. Alternatively, the dielectric film may be on the same chip (e.g., the same substrate), and the package may include two parts: one is sealed to isolate the reference dielectric film from the external atmosphere in a sealed chamber, and one is exposed to expose the main dielectric film to the external atmosphere.

[0034] In some examples, the sealed chamber may contain a vacuum or a gas, such as nitrogen, dry air, and / or any other gas or gas mixture. Since pressure affects the thermal conductivity of the gas, which in turn affects the sensor behavior, when the primary membrane is exposed to the atmosphere, preferably the sealed chamber contains dry air at substantially atmospheric pressure to minimize any effects caused by differences in the properties and behavior of the gas to which the membrane is exposed. It will be understood that if a particular application requires that the primary membrane be exposed to the external atmosphere or an external environment different from the atmosphere, the sealed chamber may preferably contain a gas or gas mixture similar to the external environment, and preferably at the same pressure.

[0035] The dielectric film exposed to the external atmosphere may be disposed in a chamber in fluid communication with the external atmosphere.

[0036] The main dielectric film may be disposed in the main chamber. The main chamber may be exposed to the external atmosphere (e.g., in fluid communication with the external atmosphere), for example, via a cover opening in the cover layer. The reference dielectric film may be disposed in the reference chamber. The reference chamber may be a sealed chamber. For example, the reference chamber may be sealed by the cover layer.

[0037] The thermal conductivity sensor may include a main cavity. The main cavity may be in fluid communication with the main chamber and / or the external atmosphere. The thermal conductivity sensor may also include a reference cavity. The reference cavity may be in fluid communication with the reference chamber.

[0038] The reference cavity may advantageously provide an increased volume for the sealed reference portion. It will be appreciated that in some cases the seal of the sealed portion may not be perfect and there may be leaks, no matter how small, into or out of the reference portion. The increased volume of the sealed reference portion means that the change in the amount or composition of the gas in the reference portion caused by any leak may be reduced as a proportion of the total volume relative to the change caused by the same leak affecting the gas in the reference chamber alone. Reducing the effects of leaks by increasing the volume of the sealed reference portion may extend the life of the sensor and / or extend the time between consecutive calibrations.

[0039] The thermal conductivity sensor may additionally include a main cavity such that the total volume occupied by the gas in the main portion and the reference portion is the same.

[0040] Preferably, the main cavity and the reference cavity (and / or the main chamber and the reference chamber) show substantially the same (or as similar as possible) thermal properties and thermal behavior. They may comprise the same material or materials and preferably the same geometry and dimensions.

[0041] The main cavity and / or the reference cavity may be provided in the substrate portion, for example they may be formed by etching the substrate portion.

[0042] The main cavity and / or the reference cavity can be in fluid communication with the main chamber or the reference chamber, respectively, via one or more openings in the intermediate layer. In some examples, one or more openings in the intermediate layer can advantageously facilitate the removal of material from the substrate portion (e.g., by etching) to form the reference cavity and / or the main cavity.

[0043] In some examples, the reference cavity can contain a vacuum or a gas, such as nitrogen, dry air, and / or any other gas or gas mixture, as discussed above with respect to the reference chamber.

[0044] It will be appreciated that when the main portion and the reference portion are provided on separate chips, each or either chip may be provided with a corresponding cavity in the same manner.

[0045] The main part may include a pressure sensor.The reference part may include a reference pressure sensor.

[0046] Any pressure sensor may be a capacitive pressure sensor in which a pair of metal plates forming a capacitor are arranged in the device so that changes in external atmospheric pressure cause the membrane and / or cover layer to deform, thereby causing the distance between the metal plates to change and the capacitance of the capacitor to change accordingly. Thus, the described arrangement provides a capacitive pressure sensor. For example, the metal plates may be arranged on opposite sides of the gap or second gap (e.g., one metal plate on the surface of the dielectric membrane opposite to the cover layer and one metal plate on the surface of the cover layer opposite to the dielectric membrane).

[0047] The metal plate may comprise aluminum, tungsten, titanium, platinum or gold or any other suitable metal or alloy.

[0048] Any pressure sensor may include a piezoresistor. The piezoresistor may be disposed in a layer (e.g., a cover layer) of the thermal conductivity sensor. Changes in atmospheric pressure may cause deformation of the layer in which the piezoresistor is disposed. Deformation of the layer may cause deformation of the piezoresistor, which may cause a change in resistance of the piezoresistor. For example, the piezoresistor may include doped single crystal silicon or polycrystalline silicon or any other suitable material.

[0049] In an embodiment including a reference pressure sensor and a main pressure sensor, the reference pressure sensor can detect the pressure change between the pressure in the sealed chamber and the ambient pressure. The main pressure sensor can be used to determine a more accurate value of the external atmospheric pressure, for example, using the reading from the reference pressure sensor. The reading from the main pressure sensor is used to correct any effects of the ambient temperature. The gas temperature in the sealed chamber can usually be substantially the same as or very close to the ambient temperature, so that the difference between the ambient temperature and the sealed chamber temperature (if any) does not have a significant effect on the pressure sensor. The two pressure sensors can be set in differential mode, for example, using a Wheatstone bridge and a differential amplifier. When additional pressure and / or temperature sensors are provided, they can be arranged as a double Wheatstone bridge, wherein each Wheatstone bridge, for example, includes four sensors to compensate for changes in ambient temperature.

[0050] In some examples, the heater (disposed to the primary film and / or the reference film) may include one or more of tungsten, platinum, titanium, molybdenum, polycrystalline silicon, single crystal silicon, and / or aluminum, or any other suitable material.

[0051] In some examples, the heater includes a transistor.

[0052] In some examples, the heater is configured to function as a temperature sensor.

[0053] In some examples, the dielectric film (eg, the main dielectric film and / or the reference dielectric film) is also provided with a temperature sensor. For example, in addition to the heater, the dielectric film may also be provided with a temperature sensor.

[0054] In some examples, the temperature sensor includes a resistor.

[0055] In some examples, the temperature sensor includes a material with a high temperature coefficient of resistance (TCR).For example, the temperature sensor may include a material with a TCR higher than the TCR of tungsten.

[0056] Advantageously, a temperature sensor comprising a material having a high TCR may provide improved sensitivity.

[0057] In some examples, the temperature sensor includes vanadium oxide, amorphous silicon and / or germanium. Advantageously, vanadium oxide, amorphous silicon and germanium are high TCR materials.

[0058] In some examples, where the dielectric film is provided with a temperature sensor, the temperature sensor is positioned relative to the heater so that the temperature sensor is sufficiently removed from the heater so that the temperature sensor is not heated to the same temperature as the heater. For example, the temperature sensor may be positioned in a region of the dielectric film that is warmer than the ambient temperature but cooler than the heater. Advantageously, positioning the temperature sensor in this manner may ensure that the temperature sensor is more stable and exhibits reduced drift over time.

[0059] For example, the temperature sensor may be laterally spaced apart from the heater (eg, the temperature sensor may be laterally spaced apart from the heater within the dielectric film).

[0060] In some examples, the dielectric film may be configured to have two microbridges (e.g., a structure formed by providing three openings in the dielectric layer). The heater may be arranged on (and / or in) a first microbridge of the two microbridges. The temperature sensor may be arranged on (and / or in) a second microbridge of the two microbridges. Arranging the heater and the temperature sensor on separate microbridges in use may provide sufficient thermal isolation of the temperature sensor from the heater to enhance the stability of the temperature sensor.

[0061] In some examples, the temperature sensor can be spaced apart from the central region of the dielectric film. For example, the temperature sensor can have a shape that can extend away from the central region of the dielectric film. Since the central region of the dielectric film tends to be the portion of the dielectric film at the highest temperature, by being removed from the central region, the temperature sensor can be more stable and less prone to drift over time.

[0062] In particular, combining one or more of the above arrangements of temperature sensors with a temperature sensor comprising a high TCR material (eg, vanadium oxide, amorphous silicon and / or germanium) may provide a highly stable temperature sensor that is less susceptible to drift.

[0063] The thermal conductivity sensor may be provided with an application specific integrated circuit (ASIC).For example, a substrate portion or chip of the thermal conductivity sensor may include an ASIC and / or other circuits.

[0064] A method of manufacturing a thermal conductivity sensor for measuring the concentration of a gas is also described herein. The method includes forming a dielectric layer on a substrate portion. The method may include forming a dielectric film in the dielectric layer, wherein the dielectric film is positioned such that a first gap exists between the dielectric film and the substrate portion. The method may include providing a heater to the dielectric film. The method may include forming a cap layer, a portion of the cap layer being positioned such that a second gap exists between the portion of the cap layer and the dielectric film.

[0065] Forming the cap layer may include micromachining the cap layer. For example, forming the cap layer may include forming the cap layer by surface micromachining.

[0066] In some examples, the cap layer is formed (and / or manufactured) using micromachining techniques.

[0067] Forming a cap layer may provide a pathway for heat transfer from the heater to the environment in a thermal conductivity sensor fabricated according to the present disclosure.

[0068] In particular, a cap layer formed by micromachining can advantageously allow very precise control of a second gap on a side of the dielectric film opposite the first gap. That is, the cap layer can be formed very close to the dielectric film, which can increase the percentage of heat transferred to the cap layer by a gas (e.g., air), thereby further increasing the sensitivity of the sensor. For example, sensitivity can be increased relative to a thermal conductivity sensor that includes a cap layer formed by wafer bonding or at the package level.

[0069] In some examples, forming the capping layer includes forming the capping layer to have a thickness of 5 μm or less.

[0070] In some examples, the method provides a thickness of the second gap of 20 μm or less.

[0071] Furthermore, advantageously, the methods described herein may provide a simpler, more cost-effective process for manufacturing thermal conductivity sensors compared to methods such as by wafer bonding or forming a cap layer at the package level.

[0072] The method may include forming a dielectric layer on a first sacrificial layer, the first sacrificial layer being between the dielectric layer and a portion of the substrate. The method may include forming one or more openings in the dielectric layer. The method may include removing (e.g., by etching) a portion of the first sacrificial layer to form a first gap in the first sacrificial layer, and forming a dielectric film over the first gap and in the dielectric layer, the dielectric film being provided with a heater.

[0073] For example, the first sacrificial layer may include a semiconductor layer and / or an insulator layer. The substrate portion and the sacrificial layer may be collectively referred to as a “substrate” and / or a “chip.” In some examples, the substrate or chip may be an SOI substrate.

[0074] In some examples, removing (eg, by etching) the first sacrificial layer includes providing an etchant through one or more openings in the dielectric layer. Advantageously, forming openings in the dielectric layer can allow for simplified removal (eg, by etching) of one or more portions of the first sacrificial layer.

[0075] The method includes forming a second sacrificial layer on the dielectric layer opposite to the first sacrificial layer, and forming a capping layer on the second sacrificial layer. The method may include removing (eg, by etching) a portion of the second sacrificial layer to form a second gap.

[0076] The second sacrificial layer may include a dielectric (eg, silicon nitride), a polymer (eg, polyamide), and / or a semiconductor material (eg, polysilicon). In some examples, the second sacrificial layer may be at most 20 μm thick.

[0077] The capping layer may be formed such that a portion of the capping layer is in direct contact with the dielectric layer, and such that a portion of the capping layer to be located over the second gap is formed over the second sacrificial layer.

[0078] The method may include forming a cap opening in the cap layer. Removing a portion of the second sacrificial layer may include providing an etchant through the cap opening.

[0079] The method may include removing (eg, by etching) a portion of the substrate to form a first gap.

[0080] It will be understood that, in general, any features of the methods described herein may be performed in any order. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0082] Figure 1 shows a cross section of an example of a thermal conductivity sensor according to the present disclosure;

[0083] Figure 2 shows a cross section of an example of an alternative thermal conductivity sensor according to the present disclosure;

[0084] Figure 3a and Figure 3b shows a cross section of an example of a thermal conductivity sensor in which a first gap is formed in a substrate portion;

[0085] Figure 4 shows a cross section of an example of a thermal conductivity sensor including a reference film;

[0086] Figure 5 A cross section showing an example of a thermal conductivity sensor of a capacitive pressure sensor pair including metal plates;

[0087] Figure 6 shows a cross section of an example of a thermal conductivity sensor including a pressure sensor, which includes two pairs of piezoresistors;

[0088] Figure 7 shows a cross section of an example of a thermal conductivity sensor fabricated by SOI technology;

[0089] Figure 8 showing a cross section of an example of a thermal conductivity sensor including a cavity in a substrate portion;

[0090] Fig. 9 A top view showing an example of a thermal conductivity sensor according to the present disclosure;

[0091] Fig.10 shows a top view of a thermal conductivity sensor including a dielectric film in the form of a microbridge;

[0092] Fig.11 A top view showing an example of a thermal conductivity sensor including a temperature sensor;

[0093] Fig.12 A top view showing an example of a thermal conductivity sensor including a dielectric film in the form of two microbridges, including a heater on a first of the two microbridges and a temperature sensor on a second of the two microbridges;

[0094] Fig.13 A top view showing an example of a thermal conductivity sensor including a temperature sensor that is not in the center of a dielectric film;

[0095] Fig.14 A cross section showing an example of a thermal conductivity sensor including one or more temperature sensors disposed in a different layer of a dielectric film than one or more heaters;

[0096] Fig.15 schematically illustrates an example of a method of manufacturing a thermal conductivity sensor according to the present disclosure;

[0097] Fig.16 (A)-(O) illustrate steps of a possible method of making a thermal conductivity sensor;

[0098] Fig.17 (A)-(P) show steps of other possible methods of making a thermal conductivity sensor. DETAILED DESCRIPTION

[0099] Figure 1 An example of a thermal conductivity sensor (also referred to herein as a device) according to the present disclosure is shown. Figure 1 As shown, the thermal conductivity sensor includes a substrate portion 1 (e.g., a silicon substrate portion) and a first sacrificial layer 3. The first sacrificial layer 3 may include, for example, a semiconductor layer and / or an insulator layer. The first sacrificial layer 3 and the substrate portion 1 may form a substrate or chip, such as a silicon on insulator (SOI) substrate.

[0100] Figure 1 The thermal conductivity sensor shown also includes a dielectric layer 24 and a dielectric film 4 formed in the dielectric layer 24. For example, the dielectric layer 24 and the dielectric film 4 may include silicon oxide or silicon nitride or some other dielectric. Preferably, the dielectric film 4 includes low stress low pressure chemical vapor deposition (LPCVD) silicon nitride or plasma enhanced chemical vapor deposition (PECVD) silicon nitride. The dielectric film 4 may also include more than one layer of the same or different materials.

[0101] A first gap 51 exists between the dielectric film 4 and the substrate portion 1 .

[0102] The heater 5 is disposed (e.g., embedded) within the dielectric film 4. The heater 5 may be a resistive heater (i.e., the heater 5 may include a resistor). The heater 5 may include tungsten, platinum, titanium, molybdenum, polycrystalline silicon, single crystal silicon, and / or aluminum. In some examples, the heater 5 includes a diode. In some examples, the heater 5 includes a metal oxide semiconductor field effect transistor (MOSFET).

[0103] The dielectric layer 24 includes one or more openings 6. The openings 6 allow the target gas to reach below the membrane (e.g., into the first gap 51), thereby allowing more surface area to be used for gas measurement. In particular, the small distance between the membrane 4 and the substrate portion 1 means that the percentage of heat transferred from the membrane 4 to the substrate through the gas is higher, thereby increasing the device sensitivity. The openings 6 may also be useful during manufacturing to enable etching of the first sacrificial layer 3 below the dielectric layer 24.

[0104] There may be additional layers (eg, material layers) between the first sacrificial layer 3 and the dielectric layer 24 .

[0105] A device according to the present disclosure may include a membrane 4 formed on top of a thin layer of a substrate. This allows a very small and well-controlled first gap 51 between the membrane and the surface of the first gap opposite the membrane 4, which may increase the sensitivity of the device due to a higher percentage of heat transferred from the membrane 4 to the surface of the first gap opposite the membrane 4 by the gas. Because the thickness of the first gap 51 can be easily controlled by the thickness of the sacrificial layer 3, the reproducibility of such a sensor is also improved.

[0106] In one example, the first gap 51 can be formed by providing a substrate portion 1, depositing a sacrificial layer 3 on the substrate portion 1, and forming a dielectric layer 24 over the sacrificial layer 3, and then removing a portion of the sacrificial layer 3. The thickness of the sacrificial layer 3 can be precisely controlled. Although a lower thickness is better for sensitivity, this can lead to manufacturing and reliability issues due to tolerances and bending of the membrane. However, depositing the sacrificial layer to the desired thickness may require a long and / or costly process, and therefore, using an SOI or similar substrate may be advantageous.

[0107] The thermal conductivity sensor according to the present disclosure can be manufactured using SOI technology. This is based on a buried oxide layer sandwiched between a top silicon layer and a thicker bottom silicon substrate portion (where Figure 1 In the embodiment, the top silicon layer and the buried oxide layer form a first sacrificial layer 3; for more details see Figure 7). The thickness of both the top silicon layer and the buried oxide can be well controlled. There are several methods to manufacture SOI substrates from smart cutting to wafer bonding. If necessary, the thickness of the top silicon layer can be increased by growing additional epitaxial silicon layers. In some examples, the top silicon layer can have a thickness between 100nm and 50μm. In some examples, the bottom silicon substrate can have a thickness between 50μm and 500μm.

[0108] The use of an SOI substrate allows the top silicon and / or buried oxide of the wafer to be used as a sacrificial layer and create etched portions with very well controlled dimensions.

[0109] Figure 1 The thermal conductivity sensor shown includes a cover layer 8. Preferably, the cover layer 8 is formed by micromachining (e.g., surface micromachining). A portion of the cover layer 8 is positioned so that a second gap 52 exists between the cover layer 8 and the dielectric film 4. In the case where the cover layer 8 is formed by micromachining, the cover layer 8 can be formed very close to the dielectric film 4 (e.g., the thickness of the second gap 52 may be 20 μm or less).

[0110] The cap layer 8 proximate to the dielectric film 4 may provide increased device sensitivity because the percentage of heat transferred to the cap layer 8 through the gas is increased.

[0111] exist Figure 1 In the example shown, a portion of the cover layer 8 is in direct contact with the dielectric layer. Figure 1 The capping layer 8 shown may be partially formed over a sacrificial layer (referred to as a second sacrificial layer) such that a portion of the capping layer 8 is located over the second gap 52 after the second sacrificial layer is removed.

[0112] Figure 2 Another example of a thermal conductivity sensor according to the present disclosure is shown, in which a cap layer 8 is in contact with a second sacrificial layer 7, wherein a portion of the second sacrificial layer 7 has been removed to form a second gap 52. Alternatively, layer 7 may be a separator layer 7 formed around the second sacrificial layer with the same thickness as the second sacrificial layer, so that the cap layer 8 may be formed on the separator layer 7 and the second sacrificial layer. It will be understood that after forming the cap layer 8, an opening will be formed in the cap layer 8, and the second sacrificial layer will be removed through the opening.

[0113] Figure 3a An example of a thermal conductivity sensor is shown in which a first gap 51 between the dielectric film 4 and the substrate portion 1 is formed in the substrate portion 1 (eg by etching a portion of the substrate portion 1 ). Figure 3b An alternative example of a thermal conductivity sensor is shown, in which a first gap 51 between the dielectric film 4 and the substrate portion 1 is formed in the substrate portion 1, the first gap 51 having a different profile. It will be appreciated that the first gap 51 may be formed in the substrate portion 1. Figure 3a and Figure 3bThe example shown omits the first sacrificial layer 3 .

[0114] Figure 4 An example of a thermal conductivity sensor is shown, which includes a main part and a reference part, each including a respective dielectric film. Figure 4 The reference portion on the right has a continuous cover layer 8, which together with the separator layer 7, the semiconductor layer 3 and the intermediate layer 2 forms a sealed reference chamber that isolates the reference film 4a from the external atmosphere. Figure 4 The main part shown on the left has a main membrane 4 exposed to the atmosphere through holes or openings 9 . Figure 4 An opening 9 is shown in the cover layer 8, but this is by no means limiting and the opening 9 may be located elsewhere as long as it provides fluid communication between the primary membrane 4 and the external atmosphere. The primary and reference parts may be used in combination in a differential circuit.

[0115] like Figure 4 As shown, the device includes a first gap 51 (referred to as a first main gap) between the main dielectric film 4 and the substrate portion 1 and a second gap 52 (referred to as a second main gap) between the main dielectric film 4 and the cover layer 8. The device also includes a first reference gap 51a between the reference dielectric film 4a and the substrate portion 1 and a second reference gap 52a between the reference dielectric film 4a and the cover layer 8.

[0116] In the examples described herein that include a main dielectric film and a second main gap and a reference dielectric film and a second reference gap, the second main gap may be configured such that a thickness of the second main gap in a direction passing through the center of the main dielectric film is less than 0.5 times (e.g., less than 0.25 times) the width of the main dielectric film.

[0117] The second reference gap may be configured such that a thickness of the second reference gap in a direction passing through a center of the reference dielectric film is less than 0.5 times (eg, less than 0.25 times) a width of the reference dielectric film.

[0118] In an example, the second main gap may have a thickness between 0.25 and 4 times the thickness of the main dielectric film. In some examples, the second reference gap may have a thickness between 0.25 and 4 times the thickness of the reference dielectric film.

[0119] In some examples, the second main gap has a thickness of at most 20 μm. In some examples, the second reference gap has a thickness of at most 20 μm.

[0120] The reference dielectric film 4a may include a reference heater 5a.

[0121] In some examples, there may be two heaters on each membrane, connected to form a Wheatstone bridge or any other suitable differential circuit. In some examples, each membrane may be provided with a temperature sensor different from the corresponding heater(s). There may be two additional temperature sensors on each membrane, connected to form a Wheatstone bridge or any other differential circuit.

[0122] The sealed chamber of the reference part may be kept under vacuum, or may be filled with nitrogen, dry air or any other gas mixture at any pressure.

[0123] Figure 5 Shown with Figure 4 The example shown is similar to that shown, which also includes two pairs of metal plates 10 and 10a. These, together with the cover layer 8, provide capacitive pressure sensors in various parts of the device. The two pressure sensors can be used to correct for the effects of pressure and / or temperature changes on the sensor readings.

[0124] Figure 6 An example of two pairs of piezoresistors 11 and 11 a providing, together with a cover layer 8 , an alternative pressure sensor is shown.

[0125] Figure 7 Shown with Figure 1 The example shown is an example of a thermal conductivity sensor similar to the example shown, where the thermal conductivity sensor is manufactured using SOI technology. Figure 7 In the example of FIG. 4 , the first sacrificial layer is a semiconductor layer 33 (eg, silicon) disposed on the intermediate layer 2 (eg, an oxide layer).

[0126] Figure 8 Shown with Figure 4 An example of a thermal conductivity sensor similar to the example of , which includes additional cavities 12, 12a in the substrate portion 1. The cavities 12, 12a can be formed by forming one or more holes or openings 13, 13a in the intermediate layer 2 and then performing, for example, isotropic etching to remove some material of the substrate portion 1. The cavity 12a is in fluid communication with the corresponding first gap 51a and second gap 52a, and is sealed to be isolated from the external atmosphere.

[0127] An advantage of this arrangement is that the amount of gas in the reference portion is increased to reduce the effect of a small leak (if any) on the amount and / or concentration of gas in the reference region.

[0128] Fig. 9 A top view of an example device is shown. A membrane 4 is supported by four beams. A heater 5 is on the membrane 4 and tracks 22 lead to bonding pads 21.

[0129] Fig.10 The membrane 4 is shown in the form of a microbridge supported at both ends. For example, the microbridge can be formed by forming the two openings 6 as slits.

[0130] Fig.11 A top view of a bridge-type membrane including a temperature sensor 18 is shown. The temperature sensor is connected to a bonding pad 21 via a track 19. The temperature sensor 18 may be a diode, a transistor or a thermopile. Alternatively, the temperature sensor 18 may be a resistive temperature sensor made of polycrystalline silicon, single crystal silicon or a metal such as tungsten, aluminum, gold or platinum or any other suitable material. Preferably, it is a resistive temperature sensor made of a material with a high TCR (temperature coefficient of resistance) such as vanadium oxide, amorphous silicon or germanium, etc. It is also possible to have a temperature sensor on a membrane of different shapes and / or configurations.

[0131] Fig.12 An example of a device with two microbridges is shown. One microbridge has a heater 5 and the other has a temperature sensor 18. Positioning the heater 5 and the temperature sensor 18 on different microbridges may provide thermal isolation of the temperature sensor 18 from the heater 5 in use.

[0132] Fig.13 An example of a temperature sensor 18 that is spaced apart from a central region of the membrane 4 is shown. For example, the temperature sensor 18 follows a path between the bonding pads 21 that avoids the central region of the membrane 4. This is because, in use, the temperature of the central region is typically higher than the rest of the membrane 4. The temperature sensor is adjacent to (or embedded in) an area of ​​the membrane 4 that is at a temperature that is higher than the ambient temperature, but still at a temperature lower than the heater. An advantage of this or similar configurations of the temperature sensor 18 is that the temperature sensor is more stable and less likely to drift over time when used at temperatures lower than the temperature of the heater. This may be particularly true for high TCR materials such as vanadium oxide, germanium, or amorphous silicon. In another example (not shown), the temperature sensor 18 may be spaced apart from the central region of the membrane 4. Fig.11 A similar arrangement is shown with the heater 5 laterally spaced apart, but the microbridge is smaller than Fig.12 It is shown wider so that the temperature sensor 18 can be located further away from the heater 5 .

[0133] Fig.14 An example of a thermal conductivity sensor is shown in which one or more temperature sensors 18 are arranged in a different layer of the dielectric film 4 than the one or more heaters 5. Fig.14 The heater(s) 5 are shown above the temperature sensor(s) 18 , but it will be understood that the heater(s) 5 may also or alternatively be located below the temperature sensor(s) 18 .

[0134] In some examples, a thermal conductivity sensor according to the present disclosure may include an ambient temperature sensor. The ambient temperature sensor may be configured to detect an ambient temperature. The ambient temperature may be used to calibrate the measurement of the temperature sensor 18.

[0135] In some examples, at least one temperature sensor (eg, an ambient temperature sensor) may be located outside of the membrane region.

[0136] The heater and temperature sensor have been shown as thin linear leads. However, it will be appreciated that they could also be circular or rectangular in shape, such as a ring shape, a multi-ring shape or a meander shape or any other suitable shape.

[0137] Fig.15 An example of a method 1500 of manufacturing a thermal conductivity sensor for measuring the concentration of a gas according to the present disclosure is schematically shown.

[0138] In step S1502 , the method 1500 includes forming a dielectric layer on a substrate.

[0139] In step S1504, method 1500 includes forming a first gap between the substrate and the dielectric layer to form a dielectric film in the dielectric layer, wherein the dielectric film is located above the first gap between the dielectric film and the substrate. Forming the dielectric film may include forming one or more openings in the dielectric layer.

[0140] In step S1506, method 1500 includes forming or providing a heater in and / or on the dielectric film. It will be appreciated that forming or providing a heater in the dielectric film may occur during formation of the dielectric film.

[0141] In step S1508, the method 1500 includes forming a capping layer and a second gap, such that the second gap is located between the capping layer and the dielectric film. Preferably, forming the capping layer includes micromachining the capping layer.

[0142] Fig.16 A method for manufacturing a thermal conductivity sensor according to the present disclosure (e.g., Figure 5 A possible method of the thermal conductivity sensor shown in FIG. 1 ) comprising the following steps:

[0143] (A) providing a substrate portion 1;

[0144] (B) forming a sacrificial layer 3 (the sacrificial layer 3 is preferably a dielectric material, but may also be a semiconductor material);

[0145] (C) depositing an initial layer of dielectric layer 24 on sacrificial layer 3;

[0146] (D) forming or providing heaters 5 and 5a on an initial layer of dielectric layer 24 (each heater may be a resistive heater made of metal, polysilicon or even single crystal silicon; the heaters may also be made as transistors, although this would involve several additional manufacturing steps);

[0147] (E) depositing another layer of dielectric layer 24;

[0148] (F) forming one or more holes in the dielectric layer 24;

[0149] (G) Portions of the sacrificial layer 3 are removed to create first gaps 51 and 51 a in the sacrificial layer 3 and to create membranes 4 and 4 a in the dielectric layer 24 over the respective first gaps 51 and 51 a.

[0150] (H) forming metal plates 10, 10a on the films 4 and 4a;

[0151] (I) depositing another sacrificial layer 31 over the membranes 4 and 4a and the metal plates 10, 10a;

[0152] (J) forming metal plates 10 and 10a on the sacrificial layer 31 and extending on the dielectric layer 24;

[0153] (K) depositing a separator layer 7 and patterning it;

[0154] (L) depositing a cap layer 8;

[0155] (M) forming holes 9 and 9a in layer 8;

[0156] (N) removing the sacrificial layer 31 through the holes 9 and 9a;

[0157] (O) The hole 9a is closed by the layer 32.

[0158] It should be noted that Fig.16 (O) also shows an alternative embodiment of the device of the present disclosure, comprising a hole 9a sealed by layer 32 above the reference portion.

[0159] Alternative structures can be made by skipping some of the steps described above. For example, if metal plates 10 and 10a are not required, steps H and J can be skipped. Step K can be skipped, resulting in a similar structure to Figure 1 A similar structure as shown.

[0160] Instead of or in addition to one or more sets of metal plates 10 , 10 a , one or more varistors may be formed or provided during the formation of the cover layer 8 .

[0161] Fig.17 A method for manufacturing a thermal conductivity sensor according to the present disclosure (e.g., according to Figure 8 Another possible method is to use a thermal conductivity sensor of

[0162] (A) providing a substrate including a substrate portion 1, an intermediate layer 2 and a semiconductor layer 3;

[0163] (B) forming one or more holes in the semiconductor layer 3 and the intermediate layer 2;

[0164] (C) filling the hole formed in step B with a sacrificial material 30 (preferably, the sacrificial material 30 is deposited so that the surface of its top is flush with the top surface of the semiconductor layer 3);

[0165] (D) depositing an initial layer of dielectric layer 24 on semiconductor layer 3;

[0166] (E) forming or providing heaters 5 and 5a (each heater may be a resistive heater made of metal, polysilicon or even single crystal silicon; the heater(s) may also be made into transistors - this may involve several manufacturing steps);

[0167] (F) depositing additional layers of dielectric layer 24;

[0168] (G) forming a hole or aperture 6 in the dielectric layer 24;

[0169] (H) removing part of the material of the semiconductor layer 3, the sacrificial layer 30 and part of the material of the substrate portion 1 (this creates gaps 51 and 51a in the semiconductor layer 3 and the corresponding membranes 4 and 4a and the cavities 12 and 12a above the gaps 51 and 51a: this can be done, for example, by etching in a single step using an etchant that etches the semiconductor layer 3, the sacrificial layer 30 and the substrate portion 1; alternatively, this can be done in multiple steps: (i) etching part of the semiconductor layer 3; (ii) etching the sacrificial layer 30; (iii) etching the substrate portion 1);

[0170] (I) forming metal plates 10, 10a on films 4 and 4a;

[0171] (J) depositing another sacrificial layer 31 on the membranes 4 and 4a and the metal plates 10, 10a;

[0172] (K) forming metal plates 10 and 10a on the sacrificial layer 31 and extending on the dielectric layer 24;

[0173] (L) depositing a separator layer 7 and patterning it;

[0174] (M) depositing a cap layer 8;

[0175] (N) creating holes 9 and 9a in layer 8;

[0176] (O) removing the sacrificial layer 31 through the holes 9 and 9a;

[0177] (P) The hole 9a is closed by the layer 32.

[0178] In an alternative process, step H may be skipped. Instead, this step may be performed after step O when the sacrificial layer 31 is removed.

[0179] Of course, a simpler structure can be created by skipping some of the above steps. For example, if metal plates 10 and 10a are not required, steps I and K can be skipped.

[0180] Instead of or in addition to one or more sets of metal plates 10 , 10 a , one or more varistors 11 , 11 a may be formed or provided during the formation of the cover layer 8 .

[0181] If layer 7 is not required, step L can be skipped.

[0182] If the metal plates 10, 10a are not required, steps I and K may be skipped.

[0183] If the cavity 12, 12a in the substrate part 1 is not required, steps B and C can be skipped.

[0184] If the pores in the intermediate layer 2 and the semiconductor layer 3 are small enough to prevent the dielectric material from entering the pores during the deposition step D, step C can be skipped.

[0185] It should be noted that Fig.16 and Fig.17 Many of the steps shown and described above may be performed using standard processes known in the semiconductor / MEMS art, such as photolithography, sputter deposition or chemical vapor deposition and etching.

[0186] Another example method of making a thermal conductivity sensor may include: starting with (e.g., obtaining or receiving) a substrate portion; depositing a dielectric layer; forming one or more holes in the dielectric layer; depositing a second sacrificial layer on the dielectric layer; depositing a cap layer on the second sacrificial layer; forming one or more holes in the cap layer; and removing part or all of the second sacrificial layer.

[0187] The method may include removing a portion of the substrate portion after creating one or more holes in the dielectric layer or as part of etching the second sacrificial layer (e.g., by etching). For example, the same etchant may be used to etch both the second sacrificial layer and the substrate portion, or different etchants may be used one after the other.

[0188] For example, the modification method may include: starting with (e.g., obtaining or receiving) a substrate portion; depositing a dielectric layer; creating one or more holes or openings in the dielectric layer; optionally removing one or more portions of the substrate portion; depositing a second sacrificial layer on the dielectric layer; depositing a capping layer over the second sacrificial layer; forming one or more holes or openings in the capping layer; removing part or all of the second sacrificial layer; and optionally removing one or more portions of the substrate portion.

[0189] In another example, a method may include a process of depositing a first sacrificial layer. The first sacrificial layer may be removed after forming a hole in the dielectric layer or as part of removing a second sacrificial layer and / or a substrate portion. For example, such a method may include: starting with (e.g., obtaining or receiving) a substrate portion; depositing a first sacrificial layer; depositing a dielectric layer; forming one or more holes or openings in the dielectric layer; optionally removing a portion of the first sacrificial layer; depositing a second sacrificial layer over the dielectric layer; depositing a cap layer on the second sacrificial layer; creating one or more holes or openings in the cap layer; etching a portion or all of the second sacrificial layer; and optionally etching a portion of the first sacrificial layer.

[0190] If the entire first sacrificial layer is etched, the method can obtain the same Figure 1 The example method in which only a portion of the first sacrificial layer is etched can produce a thermal conductivity sensor similar to that shown in FIG. Figure 2 A thermal conductivity sensor similar to that shown.

[0191] The methods described herein may also involve depositing a metal plate before and after depositing the second sacrificial layer (eg, to provide a pressure sensor to the device).

[0192] In examples of the methods described herein, the thickness of the second main gap in a direction passing through the center of the main dielectric film may be less than 0.5 times (e.g., less than 0.25 times) the width of the main dielectric film. The thickness of the second reference gap in a direction passing through the center of the reference dielectric film may be less than 0.5 times (e.g., less than 0.25 times) the width of the reference dielectric film. In some examples, the second main gap may have a thickness between 0.25 and 4 times the thickness of the main dielectric film. In some examples, the second reference gap may have a thickness between 0.25 and 4 times the thickness of the reference dielectric film. In some examples, the second main gap has a thickness of at most 20 μm. In some examples, the second reference gap has a thickness of at most 20 μm.

[0193] Forming the dielectric layer may also include other steps, such as depositing different layers of dielectric material, forming or providing a heater, and forming or providing a temperature sensor.

[0194] The skilled artisan will appreciate that in the foregoing description and the appended claims, positional terms such as "above," "below," "below," "side," and the like are made with reference to conceptual illustrations of the device, such as those showing standard cross-sectional views and those shown in the accompanying drawings. These terms are used for ease of reference and are not intended to be limiting. Therefore, these terms will be understood to refer to the device when in the orientation shown in the drawings.

[0195] Although the present disclosure is described according to the preferred embodiments as set forth above, it should be understood that these embodiments are merely illustrative and the claims are not limited to these embodiments. Those skilled in the art will be able to make modifications and substitutions based on the present disclosure, which are considered to fall within the scope of the appended claims. Each feature disclosed or shown in this specification may be incorporated into the present disclosure alone or in any appropriate combination with any other features disclosed or shown herein.

Claims

1. A thermal conductivity sensor for measuring the concentration of a gas, the sensor comprising: Base plate part; a dielectric layer comprising a dielectric film, wherein the dielectric film is provided with a heater; a first gap between the substrate portion and the dielectric film, wherein the dielectric film is located over the first gap; and micro-machined capping layer; A second gap is located between the cap layer and the dielectric film.

2. The thermal conductivity sensor according to claim 1, wherein: The capping layer is a surface micromachined capping layer, preferably, wherein the capping layer has a thickness of 5 μm or less, and / or wherein the capping layer comprises at least one of a dielectric material, a metal, silicon and polysilicon.

3. The thermal conductivity sensor according to claim 1 or claim 2, wherein: Portions of the capping layer are in direct contact with the dielectric layer.

4. The thermal conductivity sensor according to claim 1, further comprising a first sacrificial layer, wherein: The substrate portion and the first sacrificial layer are parts of a chip, and wherein the first gap is formed in the first sacrificial layer of the chip.

5. The thermal conductivity sensor according to claim 1, wherein: The thickness of the second gap is 0.5 times or less the width of the dielectric film.

6. The thermal conductivity sensor according to claim 1, wherein: The thickness of the second gap is between 0.25 and 4 times the thickness of the dielectric film.

7. The thermal conductivity sensor according to claim 1, wherein: The thickness of the second gap is 20 μm or less.

8. The thermal conductivity sensor according to claim 1, comprising a first sacrificial layer between the dielectric film and the substrate portion and / or a second sacrificial layer between the cap layer and the dielectric layer, wherein: The first gap is also located in the first sacrificial layer and optionally in the substrate portion, wherein the second gap is located in the second sacrificial layer.

9. The thermal conductivity sensor according to claim 1, wherein: The cover layer includes a cover opening.

10. The thermal conductivity sensor according to claim 1, wherein The dielectric film is a main dielectric film, and wherein the thermal conductivity sensor further comprises: A reference dielectric film having a reference heater, wherein the reference dielectric film is located above the reference gap; wherein the main dielectric film is exposed to the external atmosphere; and wherein the reference dielectric film is disposed in a sealed chamber, and optionally, wherein the main dielectric film is disposed in a main chamber, and wherein the reference dielectric film is disposed in a reference chamber; Among them, the thermal conductivity sensor includes: a main cavity in fluid communication with the main chamber; and A reference cavity is in fluid communication with the reference chamber.

11. The thermal conductivity sensor of claim 1, comprising a pressure sensor.

12. A thermal conductivity sensor for measuring the concentration of a gas, the sensor comprising: Base plate part; a dielectric layer including a main dielectric film provided with a main heater; a first main gap between the substrate portion and the main dielectric film, wherein the main dielectric film is located above the first main gap; Cap layer; a second main gap between the cap layer and the main dielectric film; and Main pressure sensor.

13. The thermal conductivity sensor according to claim 12, wherein: The dielectric layer further includes a reference dielectric film, and the thermal conductivity sensor further includes a first reference gap between the reference dielectric film and the substrate portion; a second reference gap between the cover layer and the reference dielectric film; and a reference pressure sensor; wherein the reference dielectric film is located above a first reference gap between the reference dielectric film and the substrate portion.

14. A method of manufacturing a thermal conductivity sensor for measuring the concentration of a gas, the method comprising: forming a dielectric layer on a portion of the substrate; providing a heater to the dielectric layer; forming a first gap between the substrate portion and the dielectric layer to form a dielectric film in the dielectric layer, wherein the dielectric film is provided with a heater and the dielectric film is located over the first gap between the dielectric film and the substrate portion; and forming a cap layer and a second gap over the film such that the second gap is between the cap layer and the dielectric film; The forming of the capping layer includes micromachining the capping layer.

15. The method according to claim 14, comprising: (a) forming a dielectric layer on the first sacrificial layer, wherein the first sacrificial layer is located between the dielectric layer and the substrate portion; as well as removing a portion of the first sacrificial layer to form a first gap, and / or (b) A portion of the substrate portion is removed to form a first gap.

16. The method of claim 14, comprising forming a dielectric layer on the first sacrificial layer, the first sacrificial layer being between the dielectric layer and the substrate portion; and A portion of the first sacrificial layer is removed to form a first gap, wherein The substrate portion and the first sacrificial layer are parts of the substrate.

17. The method according to any one of claims 14 to 16, comprising: forming a second sacrificial layer on the dielectric layer; forming a capping layer on the second sacrificial layer; as well as A portion of the second sacrificial layer is removed to form a second gap.

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