HEAT SENSOR BASED ON A MICRO-ELECTRO-MECHANICAL SYSTEM (MEMS) AND METHOD FOR THE PRODUCTION THEREOF

Abstract

Method for producing a thermal sensor based on a micro-electro-mechanical system, MEMS, comprising: Forming first (104) and second sensing electrodes (106) having first (108) and second electrode fingers (112) respectively on a substrate (102), wherein the first (108) and second electrode fingers (112) are formed in an interdigitated configuration and are suspended above the substrate (102); Forming a patterned layer (3960) having a rectangular cross-section between and vertically above a pair of the first electrode fingers (108); modifying the patterned layer (3960) to have a curved cross-section between the pair of first electrode fingers (108); Forming a curved sensing element (116) on the modified structured layer (3960) to couple it to the pair of first electrode fingers (108), and Removing the modified structured layer (3960).

Description

BACKGROUND

[0001] Micro-electromechanical systems (MEMS) are used in various sensor devices, such as accelerometers, pressure sensors, thermal sensors, and position sensors. The operation of MEMS sensor devices can be based on capacitive detection technology, which converts mechanical movements of sensing elements into electrical signals. The mechanical movements can occur in response to input signals received by or input to the sensing elements of the MEMS sensor devices. The electrical signals can be used to measure properties of the input signals sensed by the sensing elements.

[0002] The invention provides a method according to claim 1, a method according to claim 10, and a thermal sensor according to claim 16. Embodiments are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Aspects of this disclosure are best understood from the following detailed description when read in conjunction with the accompanying figures. It should be noted that, in accordance with common industry practice, various features are not drawn to scale. Rather, the dimensions of the various structural elements may be exaggerated or reduced as needed for clarity of discussion. Fig. 1A-1C illustrates an isometric view, a cross-sectional view, and a top view, respectively, of a MEMS thermal sensor according to some embodiments. Fig. 1A-1C illustrate an isometric view, a cross-sectional view, and a top view, respectively, of a MEMS thermal sensor according to some embodiments. Fig. 2-3 illustrate top views of a MEMS thermal sensor with various configurations of measurement contact pads according to some embodiments. Fig. 4-5 illustrate top views of a MEMS thermal sensor with different electrode finger structures according to some embodiments. Fig. 6-14 illustrate various top views of a sensing element according to some embodiments. Fig. 15-20 illustrate cross-sectional views of a MEMS thermal sensor with various configurations of sensing elements according to some embodiments. Fig. 21-28 illustrate isometric views of a MEMS thermal sensor with various configurations of sensing elements and electrode fingers according to some embodiments. Fig. 29 illustrates a cross-sectional view of a MEMS thermal sensor according to some embodiments. Fig. 30 illustrates a top view of a MEMS thermal sensor according to some embodiments. Fig. 31 is a flowchart of a method of manufacturing a MEMS thermal sensor according to some embodiments. Fig. 32A-44A illustrate isometric views of a MEMS thermal sensor at various stages of its manufacturing process, according to some embodiments. Fig. 32B-44B illustrate cross-sectional views of a MEMS thermal sensor at various stages of its manufacturing process, according to some embodiments.

[0004] Illustrative embodiments will now be described with reference to the accompanying drawings. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION

[0005] The following disclosure provides many different embodiments or examples for implementing various features of the subject matter discussed herein. Specific examples of components and arrangements are described below to simplify the present disclosure. For example, the formation of a first structural element over a second structural element in the following description may include embodiments in which the first and second structural elements are formed in direct contact, and may also include embodiments in which additional structural elements may be formed between the first and second structural elements such that the first and second structural elements are not necessarily in direct contact.For purposes of the present text, the formation of a first structural element on a second structural element means that the first structural element is formed in direct contact with the second structural element. Furthermore, the present disclosure may repeat reference numbers and / or letters in the various examples. This repetition does not automatically create a relationship between the various embodiments and / or configurations discussed.

[0006] Spatially relative terms such as "beneath," "under," "lower," "above," "upper," and the like may be used herein for convenience of description to describe the relationship of one element or feature to one or more other elements or features, as illustrated in the figures. The spatially relative terms are intended to encompass other orientations of the device in use or operation besides the orientation shown in the figures. The device may also be oriented differently (rotated 90 degrees, or other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

[0007] It should be noted that references in the specification to "one particular embodiment," "an embodiment," "an exemplary embodiment," "exemplary," etc., mean that the described embodiment may include a particular feature, structure, or characteristic, but not every embodiment includes the particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, if a particular feature, structure, or characteristic is described in connection with one embodiment, it is understood that it will be within the skill of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether expressly described or not.

[0008] It is to be understood that the phraseology or terminology used herein is for the purpose of description rather than limitation, in that the terminology or phraseology used in this specification should be interpreted by one of ordinary skill in the art in accordance with the teachings contained herein.

[0009] As used herein, the term "approximately" indicates the value of a given quantity, which may vary based on a particular technology node associated with the semiconductor device in question. In some embodiments, the term "approximately" may indicate a value of a given quantity that varies, for example, within 5-30% of the value (e.g., ±5%, ±10%, ±20%, or ±30% of the value) based on the respective technology node.

[0010] As used herein, the term "substantially" indicates the value of a given quantity, which may vary based on a particular technology node associated with the semiconductor device in question. In some embodiments, the term "substantially" may indicate a value of a given quantity, based on the respective technology node, that varies, for example, within ±5% of a target (or intended) value.

[0011] The present disclosure provides example structures of a MEMS thermal sensor and example methods for manufacturing them. The MEMS thermal sensor may be configured to measure temperatures based on capacitive sensing technology. In some embodiments, the MEMS thermal sensor may have a pair of capacitive sensing electrodes with interdigitated electrode fingers coupled to curved sensing elements. The sensing elements may be configured to sense temperature and generate mechanical movements in the electrode fingers, which may result in a change in the capacitance between the sensing electrodes. Based on the capacitance between the sensing electrodes, the MEMS thermal sensor may measure temperatures sensed by the sensing elements.

[0012] Compared to sensors with non-curved (e.g., flat) sensing elements, the curved configuration of the sensing elements disclosed herein enables bidirectional mechanical movements of the electrode fingers and, as a result, generates a wider range of mechanical movements in lateral directions in response to temperatures sensed by the curved sensing elements. In some embodiments, the range of mechanical movements of each electrode finger coupled to a curved sensing element is increased by about 10% to about 50% (e.g., about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, or about 45%) compared to sensors with non-curved sensing elements.In some embodiments, the range of mechanical movements of each electrode finger coupled to a curved sensing element may be about 1 nm to about 100 µm (e.g., about 5 nm, about 10 nm, about 20 nm, about 50 nm, about 100 nm, about 200 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 5 µm, about 7 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm).

[0013] The wider range of mechanical movements can generate a wider range of variations in the capacitance between the sensing electrodes. As a result, the MEMS thermal sensor can sense and measure a wider range of temperatures based on the capacitance between the sensing electrodes and be more sensitive to temperature variations than sensors with non-curved sensing elements. In some embodiments, the sensitivity of the MEMS thermal sensor is increased by about 10% to about 60% (e.g., about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, or about 55%) compared to sensors with non-curved sensing elements.

[0014] Fig. 1A illustrates an isometric view of a MEMS thermal sensor 100 according to some embodiments. Fig. Figure 1B illustrates a cross-sectional view along line AA of the MEMS thermal sensor 100 of Fig. 1A. Fig. 1C illustrates a top view of the MEMS thermal sensor 100 according to some embodiments. The MEMS thermal sensor 100 may include comb-shaped capacitive sensing electrodes 104 and 106 positioned facing each other on a substrate 102. The sensing electrode 104 may have a plurality of electrode fingers 108 extending from an electrode rod 110 and suspended above the substrate 102. The plurality of electrode fingers 108 extend in a direction (e.g., Y-axis) substantially perpendicular to the direction (e.g., X-axis) along which the electrode rod 110 extends. Similar to the sensing electrode 104, the sensing electrode 106 may have a plurality of electrode fingers 112 extending from an electrode rod 114 and suspended above the substrate 102.The plurality of electrode fingers 112 extend in a direction (e.g., Y-axis) substantially perpendicular to the direction (e.g., X-axis) along which the electrode rod 114 extends. The plurality of electrode fingers 108 may be positioned in an interlocking configuration with the plurality of electrode fingers 112.

[0015] The substrate 102 and / or the sensing electrodes 104 and 106 may be a semiconductor material, such as silicon. In some embodiments, the substrate 102 and / or the sensing electrodes 104 and 106 may include: an elemental semiconductor, such as silicon or germanium; a compound semiconductor, including silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, and / or indium antimonide; an alloy semiconductor, including silicon-germanium carbide, silicon-germanium, gallium arsenophosphide, gallium-indium phosphide, gallium-indium arsenide, gallium-indium arsenophosphide, aluminum-indium arsenide, and / or aluminum-gallium arsenide; or a combination thereof.

[0016] In some embodiments, the sensing electrodes 104 and 106 may include a metallic material (e.g., aluminum (Al), copper (Cu), aluminum-copper (AlCu), iron (Fe), nickel (Ni), tin (Sn), copper-nickel (CuNi), chromium (Cr), platinum (Pt), tungsten (W), titanium (Ti), tantalum (Ta), rhodium (Rh), platinum-rhodium (PtRh), tantalum nitride (TaN), nickel silicide (NiSi), cobalt (Co), cobalt silicide (CoSi), silver (Ag), tantalum carbide (TaC), titanium-aluminum (TiAl), metal alloys, and / or combinations thereof), a metal alloy, or doped or undoped polysilicon. In some embodiments, the sensing electrodes 104 and 106 may include a conductive material having an electrical resistivity in the range of about 1×10 -15 Ωm to about 1×10 15 Ωm (for example about 1×10 -12 Ωm, about 1×10 -10 Ωm, about 1×10 -9 Ωm, about 1×10 -8 Ωm, about 1×10 -7 Ωm, about 1×10 -6 Ωm, about 1×10 -5Ωm, about 1×10 -4 Ωm, about 1×10 -2 Ωm, about 1×10 Ωm, about 1×10 5 Ωm, or 1×10 10 Ωm) at room temperature (for example, about 20°C, about 23°C, or about 25°C).

[0017] As in the Fig. 1A and Fig. 1C, each of the electrode rods 110 and 114 may have a horizontal dimension L 1 along an X-axis (e.g., length) in the range of about 1 µm to about 5 mm (e.g., about 10 µm, about 50 µm, about 100 µm, 250 µm, about 500 µm, about 750 µm, about 1 mm, about 2 mm, or about 4 mm). The portion of each electrode rod 110 and 114 from which respective electrode fingers 108 and 112 extend may have a horizontal dimension W 1 (in Fig. 1C) along a Y-axis (e.g., width) in the range of about 100 nm to about 100 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm). In some embodiments, the capacitance between the sensing electrodes 104 and 106 can be measured using measuring probes directly on the electrode rods 110 and 114.

[0018] In some embodiments, the electrode rods 110 and 114 may have contact regions 110a and 114a with measurement contact pads 124 and 126, respectively, configured to measure the capacitance between the sensing electrodes 110 and 114. The measurement contact pads 124 and 126 may have first conductive layers 124a and 126a on (e.g., directly on) the contact regions 110a and 114a, respectively; or as shown in the Fig. 1A-1B, they may have additional first buffer layers 124b and 126b located between the first conductive layers 124a and 126a and the contact regions 110a and 114a, respectively. The first buffer layers 124b and 126b may include oxide or nitride materials.

[0019] In some embodiments, the contact regions 110a and 114a are not at opposite ends of an array of electrode fingers 108 (in the Fig. 1A and Fig. 1C), but may instead be positioned facing each other, as in Fig. 2, which illustrates a top view of the MEMS thermal sensor 100 with an alternative configuration of the contact regions 110a and 114a. In some embodiments, the measurement contact pads 124 and 126 may be arranged on the electrode rods 110 and 114, respectively, without the contact regions 110a and 114, as shown in Fig. 3, which illustrates a top view of the MEMS thermal sensor 100 with an alternative configuration of the measurement contact pads 124 and 126.

[0020] As in the Fig. 1B-1C, each of the electrode fingers 108 and 112 can have horizontal dimensions W 2 or W 3 along an X-axis (e.g., the widths) in the range of about 100 nm to about 100 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm). In some embodiments, the dimensions W 2 and W 3 be equal to or different from each other. In some embodiments, each of the electrode fingers 108 and 112 may have a horizontal dimension L 2along a Y-axis (e.g., length) in the range of about 100 nm to about 100 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm). In some embodiments, the electrode fingers 108 may have different lengths than the electrode fingers 112. Each of the electrode fingers 108 and 112 may have a vertical dimension H 1 along a Z-axis (e.g., height) in the range of about 100 nm to about 300 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, about 90 µm, about 100 µm, about 200 µm, or about 250 µm).

[0021] In some embodiments, adjacent electrode fingers 108 and 112 may be spaced along an X-axis by a horizontal distance S 1in the range of about 100 nm to about 100 µm apart (for example, about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm). The spaces between the electrode fingers 108 and 112 may contain a dielectric gas, such as air or nitrogen, or a dielectric liquid, such as mineral oil, polymerized butenes, castor oil, or silicone oil.

[0022] As in Fig. 1B, the electrode fingers 108 and 112 can be arranged above the substrate 102 with a vertical dimension D 1 between bottom surfaces 108s of the electrode fingers 108 and a top surface 102a of the substrate 102 and vertical distances D 2 between bottom surfaces 112b of the electrode fingers 112 and the top surface 102a. In some embodiments, the distances D 1 and D 2be equal to or different from each other. The distances D 1 and D 2 may extend along a Z-axis and may range from about 500 nm to about 500 µm (for example, about 600 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, about 90 µm, about 100 µm, about 200 µm, about 250 µm, about 300 µm, or about 400 µm). Distances D 1 and D 2 of less than 500 nm can introduce the effect of parasitic capacitance from the region between the substrate 102 and the electrode fingers 108 and 112 into the capacitance measurements between the sensing electrodes 104 and 106. The effect of parasitic capacitance in the capacitance measurements can lead to measurement errors in the MEMS thermal sensor 100. Distances D 1 and D 2equal to or greater than 500 nm can help reduce or prevent electrostatic attraction between the substrate 102 and the electrode fingers 108 and 112, which can cause sticking (stiction) between them.

[0023] The word "stiction" is derived from the words "static" and "friction" and refers to the undesirable consequence of a movable element (e.g., electrode fingers 108 and 112) in a MEMS device (e.g., MEMS thermal sensor 100) touching and sticking to a surrounding structural element. The phenomenon of stiction can occur during operation of the MEMS device and / or during device fabrication. Various environmental factors and processes that take place during MEMS device fabrication can cause stiction. For example, a plasma process during MEMS device fabrication can cause charge to build up on conductive surfaces (e.g., electrode fingers 108 and 112 or substrate 102), creating an electrostatic attraction between the movable elements and the surrounding structural elements.

[0024] As in Fig. 1C, the electrode fingers 108 and 112 can be separated from the electrode rods 114 and 110, respectively, by horizontal distances D 3 and D 4 be spaced along a Y-axis. In some embodiments, the distances D 3 and D 4 be equal to or different from each other. The distances D 3 and D 4 may be in the range of about 500 nm to about 500 µm (for example, about 600 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, about 90 µm, about 100 µm, about 200 µm, about 250 µm, about 300 µm, or about 400 µm). Distances D 3 and D 4 equal to or greater than 500 nm can help to reduce or prevent electrostatic attraction and consequently reduce or prevent stiction between the electrode fingers 108 and 112 and the electrode rods 114 and 110, respectively. Similar to the distances D 1 and D 2 can distances D3 and D 4 of less than 500 nm introduce the effect of a parasitic capacitance between the electrode fingers 108 and 112 and the electrode rods 114 and 110 into the capacitance measurements, resulting in measurement errors in the MEMS thermal sensor 100.

[0025] In some embodiments, the MEMS thermal sensor 100 may be formed instead of the electrode fingers 108 and 112, or in addition to the electrode fingers 108 and 112, with a rectangular profile along an XY plane, as in Fig. 1C, also have electrode fingers 408 and 412 with a trapezoidal profile along an XY plane, as shown in Fig. 4, and / or electrode fingers 508 and 512 with a trapezoidal profile along an XY plane, as shown in Fig. 5 shown. Fig. 4-5 illustrate top views of the MEMS thermal sensor 100 with alternative structures of the electrode fingers 108 and 112. The discussion of the electrode fingers 108 and 112 applies to the electrode fingers 408 and 412, and 508 and 512, respectively, unless otherwise stated. The trapezoidal profiles of the electrode fingers 408 and 412 taper downward along a Y-axis from free ends 408a and 412a toward fixed ends 408b and 412b, respectively. In contrast, the trapezoidal profiles of the electrode fingers 508 and 512 taper downward along a Y-axis from the fixed ends 508b and 512b toward the free ends 508a and 512a.

[0026] In some embodiments, each electrode finger 408 may have a ratio R 1a dimension of the free end 408a along an X-axis to a dimension of the fixed end 408b along an X-axis in the range of about 1:1.1 to about 1:5 (for example, about 1:1.2, about 1:1.5, about 1:1.7, about 1:2, about 1:2.2, about 1:2.5, about 1:3, about 1:3.5, about 1:4, about 1:4.2, about 1:4.5, or about 1:4.7). Each electrode finger 412 may have a ratio R 2 a dimension of the free end 412a along an X-axis to a dimension of the fixed end 412b along an X-axis of at least the ratio R 1 In some embodiments, each electrode finger 508 may have a ratio R 3a dimension of the fixed end 508b along an X-axis to a dimension of the free end 508a along the X-axis in the range of about 1:1.1 to about 1:5 (for example, about 1:1.2, about 1:1.5, about 1:1.7, about 1:2, about 1:2.2, about 1:2.5, about 1:3, about 1:3.5, about 1:4, about 1:4.2, about 1:4.5, or about 1:4.7). Each electrode finger 512 may have a ratio R 4 a dimension of the fixed end 512b along an X-axis to a dimension of the free end 512a along an X-axis of at least the ratio R 3 have.

[0027] As in the Fig. 1A-1C, the MEMS thermal sensor 100 may further include sensing elements 116. Each sensing element 116 may be disposed on a support member 120 and may be coupled to the support member 120 and a pad layer 122 by a pair of adjacent electrode fingers 108. The pad layer 122 may include a second conductive layer 122a and a second buffer layer 122b having a material composition similar to the first conductive layer 124a and the first buffer layer 124b, respectively. The sensing elements 116 may be configured to expand (e.g., expand linearly) or contract based on the temperature sensed from an object and / or an environment in which the MEMS thermal sensor 100 may be placed. The linear expansion of the sensing elements 116 can reduce their curvatures and / or increase their radii of curvature (ieit may cause the sensing elements 116 to curve less; not shown), while linearly contracting the sensing elements 116 may increase their curves and / or reduce their radii of curvature (i.e., it may cause the sensing elements 116 to curve more; not shown).

[0028] In the case of linear expansion, each linearly expanded sensing element 116 may exert shear or lateral forces in directions 128A and 128B along an X-axis on the pair of electrode fingers 108 to which it is coupled. Such shear or lateral forces may cause the pair of electrode fingers 108 to bend away from each other, as indicated by dashed lines in the Fig. 1B-1C. In the case of linear contraction, each linearly contracted sensing element 116 may exert shear or lateral forces in directions 128C and 128D along an X-axis on the pair of electrode fingers 108 such that the pair of electrode fingers 108 bends toward each other, as shown by solid black lines in the Fig. 1B-1C. Therefore, the curved configuration of the sensing elements 116 can enable bidirectional mechanical movements of each electrode finger 108, resulting in a wider range of mechanical movements compared to sensors with non-curved sensing elements, which can cause mechanical movement of each electrode finger in a specific direction. Although the dashed and solid black lines in the Fig. 1B-1C illustrate the bent electrode fingers 108 as having linear side profiles, according to some embodiments, the electrode fingers 108 may also have curved side profiles after bending.

[0029] As in the Fig. 1B-1C, the maximum displacement M of each electrode finger 108 from its initial position due to shear or lateral forces may be defined as the range of mechanical movement of the electrode fingers 108. In some embodiments, the range of mechanical movements of each electrode finger 108 coupled to a corresponding sensing element 116 may range from about 1 nm to about 100 µm (e.g., about 5 nm, about 10 nm, about 20 nm, about 50 nm, about 100 nm, about 200 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 5 µm, about 7 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm).In some embodiments, the range of mechanical movement of each electrode finger 108 coupled to a corresponding sensing element 116 is increased by about 10% to about 50% (e.g., about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, or 45%) compared to sensors with non-curved sensing elements. For effective translation of the electrode fingers 108, the sensing elements 116 can be placed closer to the free ends 108a than to the fixed ends 108b of the electrode fingers 108.

[0030] Bending the electrode fingers 108 in response to the temperature sensed by the sensing elements 116 may cause the distance between the electrode fingers 108 and 112 to change, resulting in a change in the capacitance between the sensing electrodes 104 and 106. Based on the change in capacitance, the temperature sensed by the sensing elements 116 may be determined using an electronic circuit and / or processor (not shown) coupled to the measurement contact pads 124 and 126. In some embodiments, the electronic circuit and / or processor may be parts of the MEMS thermal sensor 100 or may be external elements coupled to the MEMS thermal sensor 100.

[0031] As in the Fig. 1A-1B, in some embodiments, each sensing element 116 may include a first element 130 disposed on a second element 132. The first and second elements 130 and 132 may each comprise temperature-sensitive materials with coefficient of thermal expansion values ​​that are different from one another. As a result, the linear expansion or contraction of each sensing element 116 in response to temperatures may depend on the combined thermal effect on the first and second elements 130 and 132. For example, the sensing element 116 may expand linearly (i.e., the sensing element 116 may bend less) if the first element 130 expands less than the second element 132 in response to certain temperatures, and / or the sensing element 116 may contract linearly (i.e.,the sensing element 116 may bend more) if the first element 130 expands more than the second element 132 in response to certain temperatures.

[0032] The first and second elements 130 and 132 may have similar or different material compositions. In some embodiments, the first and second elements 130 and 132 may include temperature-sensitive materials with thermal expansion coefficient values ​​ranging from about 5 µm / m-°C to about 30 µm / m-°C (e.g., about 6 µm / m-°C, about 8 µm / m-°C, about 10 µm / m-°C, about 12 µm / m-°C, about 15 µm / m-°C, about 17 µm / m-°C, about 20 µm / m-°C, about 22 µm / m-°C, about 23 µm / m-°C, about 25 µm / m-°C, or about 27 µm / m-°C). There may be a difference of about 0.1 µm / m-°C to about 25 µm / m-°C (for example, about 0.2 µm / m-°C, about 0.5 µm / m-°C, about 0.7 µm / m-°C, about 0.9 µm / m-°C, about 1 µm / m-°C, about 1.5 µm / m-°C, about 3 µm / m-°C, about 5 µm / m-°C, about 7 µm / m-°C, about 10 µm / m-°C, about 12 µm / m-°C, about 15 µm / m-°C, about 17 µm / m-°C, about 20 µm / m-°C, or about 23 µm / m-°C) between the thermal expansion coefficient values ​​of materials of the first and second elements 130 and 132.

[0033] In some embodiments, the first and second elements 130 and 132 may include a metal, a metal alloy, a semiconductor, or a combination thereof. In some embodiments, the first and second elements 130 and 132 may include Si, Ge, Al, Cu, Fe, Ni, Cr, Pt, W, Ti, Ta, Rh, Co, Ag, Sn, AlCu, CuNi, PtRh, NiSi, CoSi, TiAl, aluminum alloy, copper alloy, nickel alloy, stainless steel, or a combination thereof. In some embodiments, the materials of the first and second elements 130 and 132 may be doped with a material such as silicon, germanium, indium, phosphorus, boron, nitrogen, or a combination thereof. The first and second elements may have different dopant materials and doping concentrations from each other.In some embodiments, the support member 120 may have a similar material composition and a similar coefficient of thermal expansion value as the first member 130 or the second member 132. In some embodiments, the support member 120 may differ from the first and second members 130 and 132 in material composition and may have a material with a coefficient of thermal expansion value that is less than about 5 µm / m-°C (for example, about 4 µm / m-°C, about 3 µm / m-°C, about 2 µm / m-°C, about 1 µm / m-°C, about 0.5 µm / m-°C, about 0.2 µm / m-°C, or about 0.1 µm / m-°C) or substantially zero. In some embodiments, the support member 120 may have a material similar to the material of the first conductive layers 124a and 126a.

[0034] At room temperature (e.g., about 20°C, about 23°C, or about 25°C), the radius of curvature of the first element 130 may be at least as large as the radius of curvature of the second element 132, and the radius of curvature of the second element 132 may be at least as large as the radius of curvature of the support element 120. In some embodiments, the first and second elements 130 and 132 may each have a radius of curvature at room temperature in the range of about 100 nm to about 25 mm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, 90 µm, about 100 µm, 250 µm, about 500 µm, about 750 µm, about 1 mm, about 2 mm, about 4 mm, about 10 mm, about 15 mm, or about 20 mm). In some embodiments, each of the sensing elements 116 may have one or more elements with temperature-sensitive materials disposed on the first element 130.The one or more elements may have radii of curvature greater than the radius of curvature of the first element 130 at room temperature. The thermal expansion coefficient values ​​of the one or more elements may be different than the thermal expansion coefficient values ​​of the first and / or second elements 130 and 132.

[0035] As in Fig. 1B, the first and second elements 130 and 132 may have thicknesses 130t and 132t, respectively, at their centers along their common central axis 134, which is substantially parallel to a Z-axis. In some embodiments, the thicknesses 130t and 132t may be the same or different from each other and may range from about 100 nm to about 10 µm (e.g., about 200 nm, about 300 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 2 µm, about 5 µm, about 7 µm, or about 9 µm). Such a thickness range may help the first and second elements 130 and 132 expand or contract linearly more effectively in response to temperature variations than thicknesses outside this range, resulting in a more sensitive MEMS thermal sensor 100. In some embodiments, the first and second elements 130 and 132 may have substantially uniform thicknesses, such as thicknesses 130t and 132t, respectively, across their bends.In some embodiments, the first and second elements 130 and 132 may have non-uniform thicknesses across their curvatures. The thicknesses of the first and second elements 130 and 132 may decrease from their central axis 134 toward their edges coupled to the electrode fingers 108.

[0036] As in Fig. 1C, the first and second elements 130 and 132 may each have a horizontal dimension L 3 (for example, length) along an X-axis and a horizontal dimension W 4 (e.g., width) along a Y-axis, with each horizontal dimension ranging from about 100 nm to about 100 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm). In some embodiments, the dimension L 3 be at least as large as the dimension W 4 .

[0037] Fig. 6-14 illustrate various top views of the first element 130 according to some embodiments. The first element 130 may comprise a rectangular section with horizontal dimensions L 3 and W 4 ( Fig. 6) in its top view. In some embodiments, the first element 130 may have a rectangular section instead of the completely blackened section of Fig. 6 a rectangular section with horizontal dimensions L 3 and W 4 and openings 736 ( Fig. 7), 836 ( Fig. 8), 936 ( Fig. 9), 1036 ( Fig. 10) or 1136 ( Fig. 11) in its plan view. The openings 736 may each have a dimension along an X-axis that is smaller than the dimension L 3 , and / or a dimension along a Y-axis that is smaller than dimension W 4, and may range from about 100 nm to about 10 µm (for example, about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, or about 7 µm). The openings 836 may each have a radius smaller than the dimensions L 3 and / or W 4 , and may range from about 100 nm to about 10 µm (for example, about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, or about 7 µm).

[0038] In some embodiments, the openings 936 may each have a dimension along an X-axis that is smaller than the dimension L 3 , and may range from about 100 nm to about 90 µm (for example, about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, or about 70 µm). The openings 936 may each have a dimension along a Y-axis that is smaller than the dimension W 4, and may range from about 100 nm to about 5 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 2 µm, or about 4 µm). In some embodiments, the openings 1036 may each have a dimension along an X-axis equal to dimension L 3 and may range from about 100 nm to about 100 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, or about 90 µm). The openings 1036 may each have a dimension along a Y-axis that is smaller than the dimension W 4 , and may range from about 100 nm to about 5 µm (for example, about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 2 µm, or about 4 µm).

[0039] As in Fig. 12, in some embodiments, the first element 130 may have first and second rectangular sections 1238a-1238b and a curved section 1240 connecting the first and second rectangular sections 1238a-1238b in its top view. The first and second rectangular sections 1238a-1238b may be curved along an X-axis by a dimension L 4 which is smaller than the dimension L 3 , in the range of about 100 nm to about 80 µm (for example, about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, or about 70 µm). As in the Fig. 13-14, according to some embodiments, the first element 130 may have one or two beams 1242 diagonally connecting the first and second rectangular sections 1238a-1238b instead of the curved section 1240. The linear expansion or contraction of the first element 130 may be implemented with a structure of one of the Fig. 7-14 shown top views may be easier than with the structure of Fig. 6. To facilitate linear expansion or contraction, the first element 130 may, according to some embodiments, have a structure of one of the types described in the Fig. 7-14 for materials with large thermal expansion coefficient values, such as thermal expansion coefficient values ​​greater than 10 µm / m-°C (e.g., about 6 µm / m-°C, about 8 µm / m-°C, about 10 µm / m-°C, about 12 µm / m-°C, about 15 µm / m-°C, about 17 µm / m-°C, about 20 µm / m-°C, about 22 µm / m-°C, about 23 µm / m-°C, about 25 µm / m-°C, or about 27 µm / m-°C). The second element 132 may have plan views similar to the plan views of the first element 130 described above with reference to Fig. 6-14 were discussed.

[0040] Fig. 15-20 illustrate cross-sectional views of the MEMS thermal sensor 100 with various configurations of the sensing elements 116 according to some embodiments. The sensing elements 116 and the support elements 120 may be coupled to the pad layers 122 such that their convex sides face the electrode fingers 108 (in Fig. 15), instead of having their concave sides facing the electrode fingers 108 (in the Fig. 1A-1B). The sensing elements 116 and / or the second element 132 may, according to some embodiments, be connected to the pad layers 122 by the support elements 120 (shown in Fig. 16-17) instead of being physically connected to top surfaces of the pad layers 122 (in the Fig. 1A-1B). The support elements 120 can have horizontal dimensions W 5 along an X-axis that are smaller than (in Fig. 16) or the same as (in Fig. 17) horizontal dimensions W 6 of the pad layers 122 along an X-axis. In some embodiments, the horizontal dimensions W 6 of the pad layers 122 be the same as (in the Fig. 15-17) or larger than (in Fig. 18) horizontal dimensions W 2the electrode fingers 108 along an X-axis. In some embodiments, the sensing elements 116 may be coupled to the electrode fingers 108 without second buffer layers 122b (in Fig. 19). In some embodiments, the sensing elements 116 may be physically connected to the electrode fingers 108 without the support elements 120 and the pad layers 122, as shown in Fig. 20 shown.

[0041] Fig. 21-28 illustrate that the MEMS thermal sensor 100, according to some embodiments, may also have different configurations of the sensing elements 116 and the electrode fingers 108 and 112 than those shown in Fig. 1A. The MEMS thermal sensor 100 may have one or more sensing elements 116 coupled to pairs of electrode fingers 108, as shown in FIGS. Fig. 21-22. Adjacent pairs of electrode fingers 108 with sensing elements 116 may form a (in Fig. 22) or multiple (not shown) electrode fingers 112 between them. The MEMS thermal sensor 100 may have sensing elements 116 coupled to pairs of electrode fingers 108, wherein two sensing elements 116 may be coupled to a common electrode finger 108, as shown in FIGS. Fig. 23-24 shown. Fig. Figure 24 further illustrates that a sensing element 116 may be coupled to a pair of electrode fingers 112. In some embodiments, the MEMS thermal sensor 100 may have more than one electrode finger 112 between each pair of electrode fingers 108 (in the Fig. 25-26), and / or more than one electrode finger 108 between each pair of electrode fingers 112 (in the Fig. 26-28 shown). Fig. 27-28 further illustrate that the sensing elements 116 may be coupled to pairs of electrode fingers 108 and 112.

[0042] As in the Fig. 29-30, according to some embodiments, the MEMS thermal sensor 100 may additionally or optionally include an overcoat layer 2944 on surfaces of the substrate 102 and the sensing electrodes 104 and 106. The overcoat layer 2944 may be configured to reduce or prevent stiction between the substrate 102 and the electrode fingers 108 and 112 and / or between the electrode fingers 108 and 112. Such a stiction phenomenon may hinder or even prevent proper operation of the MEMS thermal sensor 100 and may be mitigated with the overcoat layer 2944.

[0043] The overcoat layer 2944 may have a thickness 2944t in the range of about 10 nm to about 1 µm (for example, about 20 nm, about 50 nm, about 80 nm, about 100 nm, about 200 nm, about 500 nm, about 700 nm, or about 900 nm). In some embodiments, the overcoat layer 2944 may include one or more self-assembled monolayers or an organic material. In some embodiments, the one or more self-assembled monolayers may include silane molecules and alkyl chains or fluorinated alkyl chains. In some embodiments, the one or more self-assembled monolayers may include octadecyltrichlorosilane (OTS; C 18 H 37 Cl 3 Si), perfluorodecyltrichlorosilane (FDTS; C 10 H 4 F 17 Cl 3 Si), perfluorooctyltrichlorosilane (FOTS; C 8 H 4 Cl 3 F 13 Si), tetrahydrooctylmethyldichlorosilane (FOMDS; C 9 H 7 Cl 2 F 13Si), tetrahydrooctyltriethoxysilane (FOTES; C 14 H 19 F 13 O 3 Si), or a combination thereof.

[0044] Fig. 31 is a flowchart of an exemplary method 3100 for manufacturing the MEMS thermal sensor 100 according to some embodiments. For illustrative purposes, the operations illustrated in FIG. 3100 are described with reference to the exemplary manufacturing process for manufacturing the MEMS thermal sensor 100 as described in FIGS. Fig. 32A-44A and 32B-44B. Fig. 32A-44A are isometric views of the MEMS thermal sensor 100 at various stages of its fabrication, and Fig. 32B-44B are cross-sectional views along lines AA of respective structures of the Fig. 32A-44A, according to some embodiments. Depending on the particular applications, the operations may be performed in a different order or may not be performed at all. It should be noted that method 3100 may not provide a complete MEMS thermal sensor 100. Accordingly, it should be understood that additional processes may be performed before, during, and after method 3100, and that some other processes may only be briefly described herein. Elements in the Fig. 32A-44A and 32B-44B with the same identifiers as elements in the Fig. 1A-1C have been described above.

[0045] In operation 3105, a recess is formed in a substrate. For example, as shown in the Fig. 32A-32B, a recess 3246 may be formed in the substrate 102. The recess 3246 may have a vertical dimension D 1(e.g., depth) along a Z-axis in the range of about 500 nm to about 500 µm (e.g., about 600 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, about 90 µm, about 100 µm, about 200 µm, about 250 µm, about 300 µm, or about 400 µm) and a horizontal dimension L 5 (e.g., length) along an X-axis in the range of about 100 nm to about 5 mm (e.g., about 500 nm, about 1 µm, about 10 µm, about 50 µm, about 100 µm, 250 µm, about 500 µm, about 750 µm, about 1 mm, about 2 mm, or about 4 mm).

[0046] Forming the recess 3246 may include depositing a hard mask layer (not shown) on the substrate 102, patterning the hard mask layer on the substrate 102 to form a patterned hard mask layer, and etching the substrate 102 through the patterned hard mask layer. In some embodiments, the hard mask layer may be a thin film including silicon oxide formed, for example, using a thermal oxidation process. In some embodiments, the hard mask layer may be formed from silicon nitride, for example, using low pressure chemical vapor deposition (LPCVD) or plasma enhanced CVD (PECVD).The hard mask layer may be patterned by photolithography, including photoresist coating (e.g., spin-on), soft firing, mask alignment, exposure, post-exposure firing, photoresist development, drying (e.g., hard firing), or a combination thereof. Etching of the substrate 102 through the patterned hard mask layer may be performed, for example, using a dry etching process, a wet etching process, or a combination thereof. The dry etching process may use reactive ion etching using a chlorine- or fluorine-based etchant.

[0047] As in Fig. 31, a first sacrificial layer is formed in the recess in operation 3110. For example, as shown in the Fig. 33A-33B, a first sacrificial layer 3348 may be formed within the recess 3246. The first sacrificial layer 3348 may include an insulating material, such as an oxide, a nitride, or a combination thereof. In some embodiments, the insulating material may include, for example, silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), or a low-k dielectric material. Forming the first sacrificial layer 3348 may include: depositing the insulating material on the structure of Fig. 32A, and removing excess insulating material from the top surface 102s of the substrate 102. In some embodiments, the insulating material may be deposited using a flowable chemical vapor deposition (FCVD) process, a high density plasma (HDP) CVD process, using silane (SiH 4 ) and oxygen (O 2) as a reaction precursor, or a subatmospheric CVD (SACVD) process, where tetraethoxysilane (TEOS) and / or ozone (O 3 ) may belong to.

[0048] The deposition of the insulating material may be followed by removing excess insulating material from the top surface 102s, for example, using a chemical mechanical polishing (CMP) process or an etch-back process. The CMP process may include planarizing the deposited insulating material such that the top surface 3348s of the first sacrificial layer 3348 may be substantially coplanar with the top surface 102s of the substrate 102. The etch-back process may include one or more of a dry etch, wet etch, and / or plasma etch process to remove the excess insulating material and make the top surfaces 3348s and 102s substantially coplanar.

[0049] In some embodiments, the one or more dry etching processes may include the use of plasma dry etching with a gas mixture containing octafluorocyclobutane (C 4 F 8 ), argon (Ar), oxygen (O 2 ) and helium (He), fluoroform (CHF 3 ) and He, carbon tetrafluoride (CF 4 ), difluoromethane (CH 2 F 2 ), chlorine (Cl 2 ) and O 2 , hydrogen bromide (HBr), O 2and He, or a combination thereof, at a pressure in the range of about 1 mTorr to about 5 mTorr. In some embodiments, the one or more wet etching processes may include the use of a treatment with dilute hydrofluoric acid (DHF), an ammonium peroxide mixture (APM), a sulfur peroxide mixture (SPM), hot deionized (DI) water, or a combination thereof. In some embodiments, the one or more wet etching processes may include the use of ammonia (NH 3 ) and hydrofluoric acid (HF) as etchants and inert gases such as Ar, xenon (Xe), He, or a combination thereof. In some embodiments, the flow rate of HF and NH 3used in the etching process may each range from about 10 sccm to about 100 sccm (e.g., about 20 sccm, 30 sccm, or 40 sccm). In some embodiments, the etching process may be performed at a pressure in the range of about 5 mTorr to about 100 mTorr (e.g., about 20 mTorr, about 30 mTorr, or about 40 mTorr) and a high temperature in the range of about 50°C to about 120°C.

[0050] As in Fig. 31, in operation 3115, a pair of sensing electrodes is formed on the substrate 102. For example, as shown in the Fig. 34A-34B and 35A-35B, the formation of sensing electrodes 104 and 106 on the substrate 102 include: bonding a wafer 3450 to the top surface 102s of the structure of Fig. 33A, followed by a wafer thinning process for thinning wafer 3450 and patterning the thinned wafer 3450 to form sensing electrodes 104 and 106. Wafer 3450 may be a semiconductor material, such as silicon. In some embodiments, wafer 3450 may include: an elemental semiconductor, such as silicon or germanium; a compound semiconductor, including silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, and / or indium antimonide; an alloy semiconductor, including silicon germanium carbide, silicon germanium, gallium arsenophosphide, gallium indium phosphide, gallium indium arsenide, gallium indium arsenide, aluminum indium arsenide, and / or aluminum gallium arsenide; or a combination thereof.

[0051] In some embodiments, the wafer 3450 may include: a metallic material (e.g., aluminum (Al), copper (Cu), aluminum-copper (AlCu), iron (Fe), nickel (Ni), tin (Sn), copper-nickel (CuNi), chromium (Cr), platinum (Pt), tungsten (W), titanium (Ti), tantalum (Ta), rhodium (Rh), platinum-rhodium (PtRh), tantalum nitride (TaN), nickel silicide (NiSi), cobalt (Co), cobalt silicide (CoSi), silver (Ag), tantalum carbide (TaC), titanium-aluminum (TiAl), metal alloys, and / or combinations thereof), a metal alloy, or doped or undoped polysilicon. In some embodiments, the wafer 3450 may include a conductive or semiconductive material having an electrical resistivity in the range of about 1×10 -15 Ωm to about 1×10 15 Ωm (for example about 1×10 -12 Ωm, about 1×10 -10 Ωm, about 1×10 -9 Ωm, about 1×10 -8 Ωm, about 1×10 -7 Ωm, about 1×10 6 Ωm, about 1×10 -5 Ωm, about 1×10 -4Ωm, about 1×10 -2 Ωm, about 1×10 Ωm, about 1×10 5 Ωm, or 1×10 10 Ωm) at room temperature (for example, about 20°C, about 23°C, or about 25°C).

[0052] The wafer 3450 may be bonded to the top surface 102s using a wafer bonding process, such as fusion bonding, anodic bonding, eutectic bonding, or a suitable wafer bonding process. In the case of fusion bonding, the bonding process may include bringing the wafer 3450 and the top surface 102s into physical contact, followed by an annealing process that forms a bond (e.g., Si / Si bond, oxide / oxide bond, or oxide / Si bond) between the wafer 3450 and the top surface 102s. The annealing process may be performed at a temperature in the range of about 200°C to about 480°C (e.g., about 210°C, about 220°C, about 250°C, about 280°C, about 300°C, about 320°C, about 340°C, about 350°C, about 400°C, or about 450°C). The fusion bonding process may further include applying a force to the top surface 3450s of the wafer 3450 for a period of time before or during the annealing process.The force may range from about 0.1 N to about 5 N (e.g., about 0.5 N, about 2 N, about 3 N, or about 4 N), and the time period may range from about 10 seconds to about 10 minutes (e.g., about 30 seconds, about 1 minute, about 2 minutes, about 5 minutes, or about 7 minutes). In various embodiments, the wafer 3450 may be bonded to the top surface 102s with a polysilicon layer as a bonding interface at the interface 3452 between the wafer 3450 and the top surface 102s.

[0053] The wafer bonding process may be followed by a wafer thinning process to thin the bonded wafer 3450 to a vertical dimension H 1along a Z-axis (e.g., height) in the range of about 100 nm to about 300 µm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, about 90 µm, about 100 µm, about 200 µm, or about 250 µm). The wafer thinning process may include a grinding process, a polishing process, and / or an etching process (e.g., wet etching or dry etching) performed on the top surface 3450s of the bonded wafer 3450.

[0054] The grinding process may include grinding the bonded wafer 3450 with a grinding tool for a period of time ranging from about 30 seconds to about 10 minutes (e.g., about 40 seconds, about 1 minute, about 2 minutes, about 5 minutes, or about 7 minutes). The polishing process may include performing a CMP process on the top surface 3450s of the bonded wafer 3450. The etching process may include a dry etch (e.g., a plasma etch) or a wet etch process. The wet etching process may include etching the top surface 3450s with an etchant containing hydrofluoric acid (HF), nitric acid (HNO 3 ) or a combination thereof. In some embodiments, the etchant may be HNO 3 at a concentration in a range of about 50% to about 90% (for example, about 60%, about 70%, or about 80%). In some embodiments, the etchant may contain HNO 3at a concentration in a range of about 10% to about 50% (e.g., about 20%, about 30%, or about 40%), mixed with hydrofluoric acid (HF) at a concentration in a range of about 10% to about 50% (e.g., about 20%, about 30%, or about 40%). In some embodiments, the bonded wafer 3450 may be thinned using the grinding process, followed by the polishing process, and then the etching process.

[0055] The wafer thinning process may be followed by a patterning process to form sensing electrodes 104 and 106, as shown in the Fig. 35A-35B. The patterning process may include forming a patterned photoresist on the thinned wafer 3450 (not shown) using photolithography, and removing wafer portions of the thinned wafer 3450 that are not protected by the patterned photoresist to form sense electrodes 104 and 106. The wafer portions may be removed by a dry etching process (e.g., reactive ion etching) or a wet etching process. The first sacrificial layer 3348 may act as an etch stop layer during the etching of the wafer portions.

[0056] As in Fig. 31, in operation 3120, a second sacrificial layer is formed on the first sacrificial layer and within spaces between the pair of sensing electrodes. 35A-35B For example, as shown in FIGS. Fig. 36A-36B, a second sacrificial layer 120 on the first sacrificial layer 3348 and within the spaces 3554 (in the Fig. 35A-35B) between the sense electrodes 104 and 105. The second sacrificial layer 3656 may include an insulating material, such as an oxide, a nitride, or a combination thereof. In some embodiments, the insulating material may include, for example, silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), or a low-k dielectric material. In some embodiments, the material of the second sacrificial layer 3656 may be similar to the material of the first sacrificial layer 3348. Forming the second sacrificial layer 3656 may include: depositing the insulating material on the structure of Fig. 35A, and removing excess insulating material from top surfaces 104s and 106s of the sensing electrodes 104 and 106, respectively. In some embodiments, the insulating material may be deposited using a flowable chemical vapor deposition (FCVD) process, a high density plasma (HDP) CVD process, using silane (SiH 4 ) and oxygen (O 2 ) as a reaction precursor, or a subatmospheric CVD (SACVD) process, where tetraethoxysilane (TEOS) and / or ozone (O 3 ) may belong to.

[0057] The deposition of the insulating material may be followed by removing excess insulating material from the top surfaces 104s and 106s, for example, using a chemical mechanical polishing (CMP) process or an etch-back process. The CMP process may include planarizing the deposited insulating material such that the top surface 3656s of the second sacrificial layer 3656 may be substantially coplanar with the top surfaces 104s and 106s. The etch-back process may include one or more of a dry etch, a wet etch, and / or a plasma etch process to remove the excess insulating material and make the top surfaces 3656s, 104s, and 106s substantially coplanar.In some embodiments, the one or more dry or wet etch processes for removing excess insulating material of the second sacrificial layer 3656 may be similar to the one or more dry or wet etch processes described above for the first sacrificial layer 3348.

[0058] As in Fig. 31, buffer layers are formed on the sensing electrodes in operation 3125. For example, as shown in the Fig. 38A-38B, first buffer layers 124b and 126b are formed on the contact regions 110 and 114a of the sensing electrodes 104 and 106, respectively, and second buffer layers 122a are formed on electrode fingers 108 of the sensing electrode 104. The formation of buffer layers 122b, 124b, and 126b may include a cap layer deposition of a layer 3758 (in the Fig. 37A-37B) of buffer material (for example, oxide, nitride, or a combination thereof) on the structure of Fig. 36A, followed by a patterning process. Layer 3758 may be deposited by chemical vapor deposition (CVD), low pressure CVD (LPCVD), plasma enhanced CVD (PECVD), atomic layer deposition (ALD), plasma enhanced ALD (PEALD), physical vapor deposition (PVD), e-beam evaporation, or another suitable process. In some embodiments, layer 3758 may have a vertical dimension 3758t along a Z-axis (e.g., thickness) in the range of about 100 nm to about 10 µm (e.g., about 200 nm, about 300 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 2 µm, about 5 µm, about 7 µm, or about 9 µm). The patterning process may include forming a patterned photoresist (not shown) on layer 3758 using photolithography, and removing portions of layer 3758 not protected by the patterned photoresist to form buffer layers 122b, 124b, and 126b.The portions of layer 3758 may be removed by a dry etching process (e.g., reactive ion etching) or a wet etching process. The dry etching process may be performed using a gas mixture containing methane (CH). 4 ), oxygen (O 2 ), sulfur hexafluoride (SF 6 ), Argon (Ar), Hydrogen (H 2 ), chlorine (Cl 2 ), boron trichloride (BCl 3 ), nitrogen trifluoride (NF 3 ), hydrogen bromide (HBr), silane, or a combination thereof. In some embodiments, operation 3125 may be optional if the MEMS thermal sensor 100 may have measurement contact pads 124 and 126 that do not include respective first buffer layers 124b and 126b and have the pad layer 122 that includes the second buffer layer 122b.

[0059] As in Fig. 31, in operation 3130, curved sensing elements and support element layers are formed with one of the sensing electrodes. For example, as shown in the Fig. 43A-43B, the sensing elements 116 and the support elements 120 are formed on second conductive layers 122a formed on the electrode fingers 108 of the sensing electrode 104. The formation of the sensing elements 116 and support elements 120 may include: (i) forming a patterned layer 3960 (in the Fig. 39A-39B), (ii) performing a heat treatment on the structured layer 3960 to form a modified structured layer 3960* having a curved cross-section (shown in the Fig. 40A-40B), (iii) topcoat deposition of a support element layer 120* (shown in the Fig. 41A-41B) on the modified structured layer 3960*, (iv) cap layer deposition of a second element layer 132* (shown in the Fig. 41A-41B) on the support element layer 120*, (v) cap layer deposition of a first element layer 130* (shown in the Fig. 41A-41B) on the second element layer 132*, (vi) patterning the first and second element layers 130* and 132* to form first and second elements 130 and 132 of the sensing element 116, respectively (in the Fig. 42A-42B), and (vii) patterning the support element layer 120* to form support elements 120, first conductive layers 124a and 126a of the measurement contact pads 124 and 126, respectively, and second conductive layers 122a of the pad layers 122 (in the Fig. 43A-43B).

[0060] As in the Fig. 39A-39B, the formation of the patterned layer 3960 may involve a topcoat deposition of a layer of organic material on the pattern of Fig. 38A and patterning the layer of organic material using photolithography and an etching process (e.g., a dry or wet etch). The wet etching process may include etching with an acid, such as sulfuric acid (H 2 SO 4). The dry etching process may include reactive ion etching with a chlorine- or fluorine-based gas. In some embodiments, the dry etching process may include using a gas mixture including hydrogen, nitrogen, and argon. The gas mixture may comprise about 5% to about 20% hydrogen. The flow rate of hydrogen may range from about 20 sccm to about 100 sccm, and the flow rate of nitrogen and argon may range from about 100 sccm to about 400 sccm. The etching process may be performed for a time period ranging from about 10 s to about 90 s, at a temperature ranging from about 10°C to about 90°C, and at a pressure ranging from about 15 mTorr to about 100 mTorr.In some embodiments, the patterned layer 3960 may have a vertical dimension (e.g., height) along a Z-axis in the range of about 100 nm to about 10 µm (e.g., about 200 nm, about 300 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 2 µm, about 5 µm, about 7 µm, or about 9 µm). In some embodiments, the organic material may include a photosensitive polymeric material, such as polyimide or a suitable photoresist.

[0061] The formation of the structured layer 3960 may be followed by a heat treatment of the structured layer 3960 to form a modified structured layer 3960*, as shown in the Fig. 40A-40B. Before heat treatment, the structured layer 3960 may have a rectangular cross-section (in Fig. 39B); it can be modified to have a curved cross-section after heat treatment (in Fig. 40B) in the modified patterned layer 3960*. The curved top surfaces 3960s* of the modified patterned layer 3960* can be used to pattern the curved shapes of the sensing elements 116 and support elements 120 formed in subsequent processes. In some embodiments, the curved top surfaces 3960s* may each have a radius of curvature at room temperature in the range of about 100 nm to about 25 mm (e.g., about 200 nm, about 500 nm, about 700 nm, about 1 µm, about 5 µm, about 10 µm, about 20 µm, about 50 µm, about 70 µm, 90 µm, about 100 µm, 250 µm, about 500 µm, about 750 µm, about 1 mm, about 2 mm, about 4 mm, about 10 mm, about 15 mm, or about 20 mm).

[0062] The heat treatment may include annealing the patterned layer 3960 in a gaseous environment comprising air, nitrogen, oxygen, or a combination thereof at a temperature in the range of about 30°C to about 500°C (e.g., about 40°C, about 50°C, about 80°C, about 100°C, about 120°C, about 150°C, about 200°C, about 250°C, about 300°C, about 350°C, about 400°C, or about 450°C). The annealing process may be performed for a period of time in the range of about 1 minute to about 3 hours (e.g., about 2 minutes, about 10 minutes, about 30 minutes, about 1 hour, about 1.5 hours, about 2 hours, or about 2 hours).

[0063] As in the Fig. 41A-41B, the formation of the modified patterned layer 3960* may be followed by a cap layer deposition of the support element layer 120* on the structure of Fig. 40A, followed by a capping deposition of the second element layer 132* on the support layer 120*, and then a capping deposition of the first element layer 130* on the second element layer 132*. The deposition of the support layer 120*, the first element layer 130*, and the second element layer 132* may each be carried out using a suitable conformal deposition process, such as CVD, PECVD, ALD, PEALD, e-beam evaporation, electroplating, chemical plating, or a combination thereof. As shown in the Fig. 41A-41B, the support element layer 120*, the first element layer 130*, and the second element layer 132* may each be substantially conformal to their underlying topography. The vertical dimensions 120t*, 130t*, and 132t* may each range from about 100 nm to about 10 µm (e.g., about 200 nm, about 300 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 2 µm, about 5 µm, about 7 µm, or about 9 µm). The vertical dimensions 120t*, 130t*, and 132t* may be the same or different from each other.

[0064] The support element layer 120*, the first element layer 130*, and the second element layer 132* may be similar or different in material composition. In some embodiments, the support element layer 120*, the first element layer 130*, and the second element layer 132* may each contain a metal, a metal alloy, a semiconductor, or a combination thereof. In some embodiments, the support element layer 120*, the second element layer 132*, and the first element layer 130* may each contain Si, Ge, Al, Cu, Fe, Ni, Cr, Pt, W, Ti, Ta, Rh, Co, Ag, Sn, AlCu, CuNi, PtRh, NiSi, CoSi, TiAl, aluminum alloy, copper alloy, nickel alloy, stainless steel, or a combination thereof.In some embodiments, the materials of the support element layer 120*, the first element layer 130*, and / or the second element layer 132* may be doped with a material such as silicon, germanium, indium, phosphorus, boron, nitrogen, or a combination thereof, and may have different dopant materials and doping concentrations from one another.

[0065] In some embodiments, the first and second element layers 130* and 132* may include temperature-sensitive materials having thermal expansion coefficient values ​​ranging from about 5 µm / m-°C to about 30 µm / m-°C (e.g., about 6 µm / m-°C, about 8 µm / m-°C, about 10 µm / m-°C, about 12 µm / m-°C, about 15 µm / m-°C, about 17 µm / m-°C, about 20 µm / m-°C, about 22 µm / m-°C, about 23 µm / m-°C, about 25 µm / m-°C, or about 27 µm / m-°C). There may be a difference of about 0.1 µm / m-°C to about 25 µm / m-°C (for example, about 0.2 µm / m-°C, about 0.5 µm / m-°C, about 0.7 µm / m-°C, about 0.9 µm / m-°C, about 1 µm / m-°C, about 1.5 µm / m-°C, about 3 µm / m-°C, about 5 µm / m-°C, about 7 µm / m-°C, about 10 µm / m-°C, about 12 µm / m-°C, about 15 µm / m-°C, about 17 µm / m-°C, about 20 µm / m-°C, or about 23 µm / m-°C) between the thermal expansion coefficient values ​​of materials in the first and second element layers 130* and 132*.In some embodiments, the support element layer 120* may have a similar material composition and a similar coefficient of thermal expansion value as the first element layer 130* or the second element layer 132*. In some embodiments, the support element layer 120* may differ from the first and second element layers 130* and 132* in material composition and may have a material with a coefficient of thermal expansion value that is less than about 5 µm / m-°C (for example, about 4 µm / m-°C, about 3 µm / m-°C, about 2 µm / m-°C, about 1 µm / m-°C, about 0.5 µm / m-°C, about 0.2 µm / m-°C, or about 0.1 µm / m-°C) or substantially zero.

[0066] The cap layer deposition of the first element layer 130* may be followed by patterning of the first and second element layers 130* and 132* to form first and second elements 130 and 132 of the sensing element 116, as shown in FIGS. Fig. 42A-42B. Patterning the first element layer 130* may include forming a patterned photoresist on the first element layer 130* using photolithography, and selectively removing portions of the first element layer 130* not protected by the patterned photoresist to form first elements 130. In some embodiments, forming the first elements 130 may be followed by selectively removing portions of the second element layer 132* not covered by overlying first elements 130 to form second elements 132.Alternatively, in some embodiments, the formation of the first elements 130 may be followed by patterning the photoresist using photolithography to cover the first elements 130, and then selectively removing portions of the second element layer 132* not covered by overlying first elements 130 protected by an overlying patterned photoresist. This alternative method of forming second elements 132 may be used to prevent overetching of the first element layer 130* when materials of the first and second element layers 130* and 132* are similar and / or the etch selectivity between the materials of the first and second element layers 130* and 132* is between about 1 and about 10 (e.g., about 2, about 5, or about 8).

[0067] The process of removing the portions of the first and second element layers 130* and 132* may include a dry or wet etching process, respectively. In some embodiments, the dry etching process may include the use of a gas mixture comprising: CH 4 , O 2 , SF 6 , Ar, H 2 , Cl 2 , BCl 3 , NF 3 , HBr, silane, or a combination thereof; hydrogen bromide (HBr), O 2 , Fluoroform (CHF 3 ) and Cl 2 ; HBr, O 2 , Cl 2 and / or nitrogen (N 2 ) at a pressure of about 45 mTorr to about 60 mTorr; HBr, O 2 , Cl 2 , N 2 and argon (Ar) at a pressure of about 45 mTorr to about 60 mTorr; or HBr, O 2 , Cl 2 and N 2 at a pressure of about 45 mTorr to about 60 mTorr. In some embodiments, the dry etching process may involve the use of a gas mixture containing BCl3 and Cl 2 containing, with a flow rate of Cl 2 between about 0 and 200 sccm and a flow rate of BCl 3 between about 10 and 200 sccm. The dry etching process may be performed at an RF power between about 50 and 2000 watts and a pressure between about 5 and 200 mT. In some embodiments, the wet etching process may include the use of an etchant comprising phosphoric acid, nitric acid, acetic acid, dilute hydrofluoric acid, hydrochloric acid, sulfuric acid, or a combination thereof. The etching process parameters for removing portions of the first and second device layers 130* and 132* may be similar to or different from each other.

[0068] The formation of the second element 132 may be followed by patterning the support element layer 120* to simultaneously form the support elements 120, the first conductive layers 124a and 126a of the measurement contact pads 124 and 126, respectively, and the second conductive layers 122a of the pad layers 122. Patterning the support element layer 120* may include forming a patterned photoresist on the support element layer 120* using photolithography, and selectively removing portions of the support element layer 120* not protected by the patterned photoresist to form support elements 120, first conductive layers 124a and 126a, and second conductive layers 122a, as shown in FIGS. Fig. 43A-43B. The process of removing portions of the support layer 120* may include a dry or wet etching process. In some embodiments, the dry etching process may include the use of a gas mixture containing CH4 , O 2 , SF 6 , Ar, H 2 , Cl 2 , BCl 3 , NF 3 , HBr, silane, or a combination thereof. In some embodiments, the wet etching process may include the use of an etchant comprising phosphoric acid, nitric acid, acetic acid, dilute hydrofluoric acid, hydrochloric acid, sulfuric acid, or a combination thereof.

[0069] In some embodiments, the first and second elements 130 and 132 and the support elements 120 may be formed in a different sequence of manufacturing steps than the sequence of manufacturing steps discussed above. For example, instead of forming the second elements 132, followed by the first elements 130, and then the support elements 120, the support elements together with the first conductive layers 124a and 126a and the second conductive layers 122a may be formed first, followed by the formation of the second elements 132, and then the first elements 130. In this exemplary case, the sequence of manufacturing steps after the formation of the modified patterned layer 3960* may include: (i) capping the support element layer 120* on the structure of Fig. 40A, (ii) patterning the support element layer 120* using photolithography and an etching process to simultaneously form the support elements 120, the first conductive layers 124a and 126a, and the second conductive layers 122a of the pad layers 122, (iii) cap layer deposition of the second element layer 132*, (iv) patterning the second element layer 132* using photolithography and an etching process to form second elements 132, (v) cap layer deposition of the first element layer 130*, and (vi) patterning the first element layer 130* using photolithography and an etching process to form first elements 130.

[0070] In another alternative embodiment, the support elements together with the first conductive layers 124a and 126a and the second conductive layers 122a may be formed first, followed by the formation of the first elements 130 and then the second elements 132. In this case, the sequence of manufacturing steps after the formation of the modified structured layer 3960* may include: (i) cap layer deposition of the support element layer 120* on the structure of Fig. 40A, (ii) patterning the support element layer 120* using photolithography and an etching process to simultaneously form the support elements 120, the first conductive layers 124a and 126a, and the second conductive layers 122a of the pad layers 122, (iii) capping the second element layer 132*, (iv) capping the first element layer 130* on the second element layer 132*, (v) patterning the first element layer 130* using photolithography and an etching process to form first elements 130, and (vi) selectively removing portions of the second element layer 132* not covered by overlying first elements 130 to form second elements 132.

[0071] As in Fig. 31, in operation 3135, the modified structured layer and the first and second sacrificial layers are removed. For example, as shown in the Fig. 44A-44B, the modified patterned layer 3960* and the first and second sacrificial layers 3348 and 3656 may be removed after the formation of the sensing elements 116, the support elements 120, the measurement contact pads 124 and 126, and the pad layers 122. In some embodiments, the modified patterned layer 3960* may be removed using a dry etching process (e.g., reactive ion etching) or a wet etching process (e.g., an etchant containing sulfuric acid). Removal of the modified patterned layer 3960* may be followed by removal of the first and second sacrificial layers 3348 and 3656 using a dry etching process (e.g., reactive ion etching) or a wet etching process (e.g., an etchant containing dilute hydrofluoric acid).

[0072] Additionally or optionally, in some embodiments, the removal of the first and second sacrificial layers 3348 and 3656 may be followed by the formation of the overlay layer 2944 (in the Fig. 2-3) on the structure of Fig. 44A. In some embodiments, the overcoat layer 2944 may include one or more self-assembled monolayers or an organic material. In some embodiments, the overcoat layer 2944 may be formed by a vapor process (e.g., a molecular vapor deposition (MVD) process) or a suitable deposition process for depositing self-assembled monolayers or organic material.

[0073] The present disclosure provides example structures of a MEMS thermal sensor and example methods for manufacturing them. The MEMS thermal sensor may be configured to measure temperatures based on capacitive detection technology. In some embodiments, the MEMS thermal sensor may include a pair of capacitive sensing electrodes (e.g., sensing electrodes 104 and 106) with interdigitated electrode fingers (e.g., electrode fingers 108) coupled to curved sensing elements (e.g., sensing elements 116). The sensing elements may be configured to sense temperature and generate mechanical movements in the electrode fingers, which may result in a change in the capacitance of the sensing electrodes. Based on the capacitance of the sensing electrodes, the MEMS thermal sensor may measure temperatures sensed by the sensing elements.

[0074] Compared to sensors with non-curved (e.g., flat) sensing elements, the curved configuration of the sensing elements disclosed herein (e.g., sensing elements 116) enables bidirectional mechanical movements of the electrode fingers (e.g., electrode fingers 108) and, as a result, generates a wider range of mechanical movements in lateral directions in response to temperatures sensed by the curved sensing elements (e.g., sensing elements 116). In some embodiments, the range of mechanical movements of each electrode finger coupled to a curved sensing element is increased by about 10% to about 50% (e.g., about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, or about 45%) compared to sensors with non-curved sensing elements.In some embodiments, the range of mechanical movements of each electrode finger coupled to a curved sensing element may range from about 1 nm to about 10 µm (e.g., about 5 nm, about 10 nm, about 20 nm, about 50 nm, about 100 nm, about 200 nm, about 500 nm, about 700 nm, about 900 nm, about 1 µm, about 5 µm, about 7 µm, or about 9 µm).

[0075] The wider range of mechanical movements may generate a wider range of variations in the capacitance of the sensing electrodes (e.g., sensing electrodes 104 and 106). As a result, the MEMS thermal sensor (e.g., MEMS thermal sensor 100) may sense and measure a wider range of temperatures and may be more sensitive to temperature variations based on the capacitance of the sensing electrodes compared to sensors with non-curved sensing elements. In some embodiments, the sensitivity of the MEMS thermal sensor is increased by about 10% to about 60% (e.g., about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, or about 55%) compared to sensors with non-curved sensing elements.

[0076] In some embodiments, a method of fabricating a micro-electro-mechanical system (MEMS) thermal sensor includes forming first and second sensing electrodes having first and second electrode fingers, respectively, on a substrate, and forming a patterned layer having a rectangular cross-section between a pair of the first electrode fingers. The first and second electrode fingers are formed in an interdigitated configuration and suspended above the substrate. The method further includes modifying the patterned layer to have a curved cross-section between the pair of first electrode fingers, forming a curved sensing element on the modified patterned layer to couple to the pair of first electrodes, and removing the modified patterned layer.

[0077] In some embodiments, a method of fabricating a device includes forming first and second sensing electrodes with movable first and second electrode fingers, respectively, on a substrate; and forming a patterned layer having a curved cross-section between a pair of the first electrode fingers. The first and second electrode fingers are formed in an interdigitated configuration. The method further includes forming a curved support member on the patterned layer to couple to the pair of first electrodes, forming a curved sensing element on the curved support member, and removing the modified patterned layer.

[0078] In some embodiments, a micro-electro-mechanical system (MEMS)-based device includes a first sensing electrode having a plurality of first electrode fingers and a second sensing electrode having a plurality of second electrode fingers. The plurality of first and second electrode fingers are arranged in an interdigitated configuration and suspended above a substrate. The MEMS device further includes a curved sensing element coupled to adjacent first electrode fingers of the plurality of first electrode fingers. The curved sensing element is configured to move the adjacent first electrodes and change a capacitance between the first and second sensing electrodes in response to a temperature sensed by the curved sensing element.The MEMS device further includes a circuit coupled to the first and second sensing electrodes and configured to measure the temperature based on the capacitance between the first and second sensing electrodes.

Claims

[1] Method for manufacturing a thermal sensor based on a micro-electro-mechanical system, MEMS, comprising: Forming first (104) and second sensing electrodes (106) having first (108) and second electrode fingers (112) respectively on a substrate (102), wherein the first (108) and second electrode fingers (112) are formed in an interdigitated configuration and are suspended above the substrate (102); Forming a patterned layer (3960) having a rectangular cross-section between and vertically above a pair of the first electrode fingers (108); modifying the patterned layer (3960) to have a curved cross-section between the pair of first electrode fingers (108); Forming a curved sensing element (116) on the modified structured layer (3960) to couple it to the pair of first electrode fingers (108), and Removing the modified structured layer (3960). [2] The method of claim 1, wherein modifying the patterned layer (3960) comprises annealing the patterned layer (3960). [3] The method of claim 1 or 2, wherein forming the first (104) and second sensing electrodes (106) comprises: Forming a recess (3246) in the substrate (102); Bonding a wafer to raised regions on a side of the substrate (102) in which the recess (3246) is located; and Thinning the bonded wafer. [4] The method of claim 3, further comprising: forming a first sacrificial layer (3348) in the recess (3246); Forming a second sacrificial layer (3656) on the first sacrificial layer (3348) and within spaces between the first (108) and second electrode fingers (112); and Removing the first (3348) and second sacrificial layers (3656) after removing the modified structured layer (3960). [5] A method according to any one of the preceding claims, further comprising: Forming a support element (120) between the curved sensing element (116) and the modified structured layer (3960). [6] A method according to any one of the preceding claims, wherein forming the curved sensing element (116) comprises: Forming a second element (132) of the curved sensing element (116); and Forming a first element (130) of the curved sensing element (116) after forming the second element (132), wherein the first element (130) is formed on the second element (132). [7] The method of any one of claims 1 to 4, wherein forming the curved sensing element (116) comprises: Forming a second element (132) of the curved sensing element (116); and Forming a first element (130) of the curved sensing element (116) after forming the second element (132), wherein the first element (130) is formed on the second element (132), the method further comprising forming a support element (120) after forming the first element (132). [8] The method of any one of the preceding claims 1 to 6, wherein forming the curved sensing element (116) comprises: depositing a second element layer on the modified structured layer (3960); depositing a first element layer on the second element layer; Structuring the first element layer to form a first element (130) of the curved sensing element (116); and Etching the second element layer to form a second element (132) of the curved sensing element (116), wherein the first element (130) is formed on the second element (132). [9] A method according to any one of the preceding claims, wherein forming the structured layer (3960) comprises: depositing a layer of polymeric material; and Structuring the layer of polymer material. [10] A method of manufacturing a thermal sensor comprising: Forming first (104) and second sensing electrodes (106) with movable first (108) and second electrode fingers (112) respectively on a substrate (102), wherein the first (108) and second electrode fingers (112) are formed in an interdigitated configuration; Forming a structured layer (3960*) having a curved cross-section between and vertically above a pair of the first electrode fingers (108); Forming a curved support element (120) on the patterned layer (3960*) to couple it to the pair of first electrodes (108); Forming a curved sensing element (116) on the curved support element (120); and Removing the textured layer (3960*). [11] The method of claim 10, wherein forming the structured layer (3960*) with the curved cross-section comprises: Forming a structured layer (3960) having a rectangular cross-section between the pair of first electrode fingers (108); and Healing the structured layer (3960) with the rectangular cross-section. [12] The method of claim 10 or 11, wherein forming the curved sensing element (116) on the curved support element comprises: depositing a second element layer on the curved support element (116); depositing a first element layer on the second element layer; Structuring the first element layer to form a first element (130) of the curved sensing element (116); and Etching the second element layer to form a second element (132) of the curved sensing element (116), wherein the first element (130) is formed on the second element (132). [13] The method of any one of the preceding claims 10 or 11, wherein forming the curved sensing element (116) on the curved support element (120) comprises: depositing a second element layer on the curved support element (120); Structuring the second element layer to form a second element (132) of the curved sensing element (116), depositing a first element layer on the second element (132); and Structuring the first element layer to form a first element (130) of the curved sensing element (116). [14] The method of any one of the preceding claims 10 to 13, wherein forming the first (104) and second sensing electrodes (106) comprises: Forming a recess (3246) in the substrate (102); Bonding a wafer to raised regions on a side of the substrate (102) in which the recess (3246) is located; and Thinning the bonded wafer. [15] The method of any one of the preceding claims 10 to 14, further comprising forming buffer layers between the curved support member (120) and the first electrode fingers (108). [16] Thermal sensor based on a micro-electro-mechanical system, MEMS, comprising: a first sensing electrode (104) having a plurality of first electrode fingers (108); a second sensing electrode (106) having a plurality of second electrode fingers (112), wherein the plurality of first (108) and second electrode fingers (112) are arranged in an interdigitated configuration and suspended above a substrate (102); a curved sensing element (116) coupled to adjacent first electrode fingers (108) of the plurality of first electrode fingers (108), the curved sensing element (116) configured to move the adjacent first electrodes (108) and change a capacitance between the first (104) and second sensing electrodes (106) in response to a temperature sensed by the curved sensing element (116); and Circuits coupled to the first (104) and second sensing electrodes (106) and configured to measure the temperature based on the capacitance between the first (104) and second sensing electrodes (106). [17] The MEMS-based thermal sensor of claim 16, wherein the curved sensing element (116) is configured to move the adjacent first electrode fingers (108) away from each other in response to the temperature sensed by the curved sensing element (116). [18] A MEMS-based thermal sensor according to claim 16 or 17, wherein the curved sensing element (116) comprises: a first element (130) having a first coefficient of thermal expansion value; and a second element (132) having a second coefficient of thermal expansion different from the first coefficient of thermal expansion value. [19] A MEMS-based thermal sensor according to claims 16 to 18, wherein the curved sensing element (116) is coupled to the adjacent first electrode fingers (108), a convex side of the curved sensing element (116) facing the adjacent first electrode fingers (108).

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