Microbolometer with Reduced Pixel Pitch

Abstract

The present disclosure relates to a microbolometer, which includes an array of pixels, each pixel includes one or more detection units, and each detection unit includes an absorption layer (530), wherein: the pitch of the detection units in at least one direction in the plane of the pixel array is between 5 and 11 μm; the pixel fill factor FF of the absorption layer (530) of one or more detection units in each pixel is in the range of 0.10 to 0.50; and the sheet resistance Rs of the absorption layer (530) of each detection unit is between 16 and 189 ohm / sq.

Description

[0001] Cross - reference to related applications

[0002] This patent application claims priority to a French patent application filed on June 5, 2019, and assigned application number FR1905962, the content of which is incorporated herein by reference. Technical field

[0003] The present disclosure generally relates to the field of infrared imaging, and more particularly to a microbolometer and a method of manufacturing a microbolometer. Background art

[0004] A microbolometer is an uncooled infrared (IR) camera for capturing thermal images of an image scene. Such an infrared camera typically includes an arrangement of infrared - sensitive detectors forming a pixel array. Each pixel of the pixel array converts the temperature measured at the pixel into a corresponding electrical signal, typically a voltage, which is then converted by an ADC (analog - to - digital converter) into a digital output signal.

[0005] Each pixel of the microbolometer includes a membrane suspended over a substrate. The membrane includes an absorption layer that absorbs energy from infrared light irradiating the pixel, causing its temperature to increase according to the intensity of the infrared light. For example, the membrane also includes a thermal layer having the property of changing its resistance by such a temperature rise, and thus the pixel can be read out by detecting the change in resistance of the thermal layer, which is thermally connected to the absorption layer.

[0006] It is generally desirable for the microbolometer to have a relatively high sensitivity within the target wavelength range, which generally means a higher absorption rate. It is also desirable for the device to be relatively compact and of relatively low cost.

[0007] However, there are technical problems in reducing the size and / or cost of the microbolometer without reducing its sensitivity. In fact, the smaller the pixel pitch of the microbolometer, the lower the amount of absorbed power, and the more difficult it is to design the arms for supporting an absorption layer having a relatively high thermal resistance. Summary of the invention

[0008] An object of embodiments of the present disclosure is to at least partially solve one or more problems in the prior art.

[0009] According to one embodiment, a microbolometer including a pixel array is provided, each pixel including one or more detection units, each detection unit including an absorption layer, wherein: the pitch of the detection units in at least one direction in the plane of the pixel array is between 5 and 11 μm; the pixel fill factor FF of the absorption layer of one or more detection units in each pixel is in the range of 0.10 to 0.50; and the sheet resistance Rs of the absorption layer of each detection unit is between 16 and 189 ohm / sq.

[0010] According to one embodiment, the ratio Rs / FF of each pixel of the array is between 200 and 600 ohm / sq.

[0011] According to one embodiment, each pixel has a pixel fill factor in the range of 0.10 to 0.40.

[0012] According to one embodiment, each pixel has a pixel fill factor in the range of 0.20 to 0.40.

[0013] According to one embodiment, the pitch of the detection units in at least one direction in the plane of the pixel array is between 8 and 9 μm.

[0014] According to one embodiment, each pixel of the array has:

[0015] - a pixel fill factor FF equal to or greater than 0.40 and less than 0.50, and the sheet resistance Rs of the absorption layer is at least 75 ohm / sq; or

[0016] - a pixel fill factor FF equal to or greater than 0.30 and less than 0.40, and the sheet resistance Rs of the absorption layer is at least 50 ohm / sq; or

[0017] - a pixel fill factor FF equal to or greater than 0.20 and less than 0.30, and the sheet resistance Rs of the absorption layer is at least 25 ohm / sq; or

[0018] - a pixel fill factor FF equal to or greater than 0.10 and less than 0.20, and the sheet resistance Rs of the absorption layer is at least 16 ohm / sq.

[0019] According to one embodiment, the ratio Rs / FF is in the range of 377 ohm / sq ± 20%.

[0020] According to one embodiment, the absorption layer of each detection unit is a metal layer.

[0021] According to one embodiment, the absorption layer is formed of TiN and has a thickness between 10 and 115 nm.

[0022] According to one embodiment, a pixel array includes a substrate, and each pixel of the pixel array includes a reflective layer formed on the substrate and a film suspended over the reflective layer. A quarter-wavelength resonator is formed between the film and the reflective layer in each pixel, and the film includes an absorption layer and a thermal layer.

[0023] According to one embodiment, the surface area of the absorption layer is less than 75% of the surface area of the film.

[0024] According to one embodiment, the height of the quarter-wavelength resonator is in the range of 1.5 to 3.5 μm.

[0025] According to one embodiment, the pitch of the detection units in at least one direction in the plane of the pixel array is less than four times the height of the quarter-wavelength resonator.

[0026] According to another aspect, a method of manufacturing a microbolometer array is provided. The method includes: forming an array of pixels, each pixel having one or more detection units, wherein forming the array includes: forming detection units having a pitch of 5 to 11 μm on at least one axis in the plane of the pixel array; and forming each detection unit to include an absorption layer having a pixel fill factor FF in the range of 0.10 to 0.50 and a sheet resistance Rs between 16 and 189 ohm / sq.

[0027] According to yet another aspect, a microbolometer is provided that includes an array of pixels, each pixel including one or more detection units, each detection unit including an absorption layer that forms a quarter-wavelength resonator having a height h between 1.5 and 5 μm, wherein the pitch of the detection units in at least one axis in the plane of the pixel array is in the range of 2.4h to 3.6h.

[0028] According to one embodiment, the pixel fill factor FF of the absorption layer of one or more detection units in each pixel is in the range of 0.20 to 0.70.

[0029] According to one embodiment, the pixel fill factor FF of the absorption layer of one or more detection units in each pixel is in the range of 0.10 to 0.50.

[0030] According to one embodiment, the pitch of the detection units is in the range of 4 to 15 μm.

[0031] According to one embodiment, the pitch of the detection units is in the range of 5 to 11 μm.

[0032] According to one embodiment, the absorption layer is a metal layer having a sheet resistance of 189 ohm / sq or less.

[0033] According to one embodiment, the absorption layer is a metal layer having a sheet resistance of 126 ohm / sq or less.

[0034] According to one embodiment, the absorption layer is formed of titanium nitride.

[0035] According to one embodiment, the resonator cavity height is between 1.5 and 3.5 μm.

[0036] According to one embodiment, each pixel of the array has:

[0037] - a pixel fill factor FF equal to or greater than 0.40 and less than 0.50, and the sheet resistance Rs of the absorption layer is at least 75 ohm / sq; or

[0038] - a pixel fill factor FF equal to or greater than 0.30 and less than 0.40, and the sheet resistance Rs of the absorption layer is at least 50 ohm / sq; or

[0039] - a pixel fill factor FF equal to or greater than 0.20 and less than 0.30, and the sheet resistance Rs of the absorption layer is at least 25 ohm / sq; or

[0040] - a pixel fill factor FF equal to or greater than 0.10 and less than 0.20, and the sheet resistance Rs of the absorption layer is at least 16 ohm / sq.

[0041] According to one embodiment, the ratio Rs / FF of each pixel of the array is between 200 and 600 ohm / sq.

[0042] According to one embodiment, the ratio Rs / FF of each pixel of the array is within 20% of 377 ohm / sq.

[0043] According to one embodiment, each detection unit includes a film including an absorption layer, a thermal layer, and a dielectric layer.

[0044] According to another aspect, there is provided a method of manufacturing a microbolometer, the method including forming a pixel array, each pixel including one or more detection units, wherein forming the array includes: forming each detection unit to include an absorption layer that forms a quarter-wavelength resonator cavity having a height h between 1.5 and 5 μm; and forming detection units having a spacing in the range of 2.4h to 3.6h on at least one axis in the plane of the pixel array. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The above and other features and advantages will be described in detail in the following description of specific embodiments given in a diagrammatic manner and are not limited to reference to the accompanying drawings, in which:

[0046] Figure 1Schematically shows an image capture circuit of an infrared camera according to an exemplary embodiment;

[0047] Figure 2 Is a cross-sectional view of a pixel of a microbolometer according to an exemplary embodiment;

[0048] Figure 3 Is a plan view of a part of a microbolometer array according to an exemplary embodiment;

[0049] Figure 4 Is a graph showing the function relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, in the case where the pixel pitch is 17 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0050] Figure 5 Is a perspective view of a pixel of a microbolometer according to an exemplary embodiment of the present disclosure;

[0051] Figure 6 Is according to an exemplary embodiment of the present disclosure Figure 5 Of a cross-sectional view of a part of a pixel;

[0052] Figure 7 Is a graph showing the function relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, in the case where the pixel pitch is 8.5 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0053] Figure 8 Is a plan view of a part of a microbolometer array according to an exemplary embodiment of the present disclosure;

[0054] Figure 9 Is a plan view of a part of a microbolometer array according to another exemplary embodiment of the present disclosure;

[0055] Figure 10 Is a graph showing the function relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for many different sheet resistances of the absorption layer, in the case where the pixel pitch is 8.5 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0056] Figure 11 Is a graph showing the function relationship between the absorption rate gain of the absorption layer of a microbolometer pixel and the pixel fill factor for many different sheet resistances of the absorption layer, in the case where the pixel pitch is 8.5 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0057] Figure 12 is a graph that shows in more detail Figure 11 the region of the graph corresponding to a gain of 20% or more;

[0058] Figure 13 is a graph that shows more specifically Figure 11 the region of the graph in

[0059] Figure 14 is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the sheet resistance / fill factor ratio for different fill factors;

[0060] Figure 15 is a graph that shows in more detail Figure 14 the region of the graph in

[0061] Figure 16 is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, where the pixel pitch is 11 μm, the Fabry - Perot cavity height is 3.5 μm, and the optical wavelength is 13 μm;

[0062] Figure 17 is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, where the pixel pitch is 5 μm, the Fabry - Perot cavity height is 1.5 μm, and the optical wavelength is 6 μm;

[0063] Figure 18 is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, where the pixel pitch is 5 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0064] Figure 19 is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, where the pixel pitch is 6 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0065] Figure 20 is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer, where the pixel pitch is 7 μm, the Fabry - Perot cavity height is 2.5 μm, and the optical wavelength is 10 μm;

[0066] Figure 21 It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer under the conditions of a pixel pitch of 8 μm, a Fabry - Perot cavity height of 2.5 μm, and an optical wavelength of 10 μm;

[0067] Figure 22 It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different thicknesses of the absorption layer under the conditions of a pixel pitch of 9 μm, a Fabry - Perot cavity height of 2.5 μm, and an optical wavelength of 10 μm;

[0068] Figure 23 It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer under the conditions of a pixel pitch of 10 μm, a Fabry - Perot cavity height of 2.5 μm, and an optical wavelength of 10 μm;

[0069] Figure 24 It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer under the conditions of a pixel pitch of 11 μm, a Fabry - Perot cavity height of 2.5 μm, and an optical wavelength of 10 μm;

[0070] Figure 25 It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the pixel fill factor for eight different sheet resistances of the absorption layer under the conditions of a pixel pitch of 12 μm, a Fabry - Perot cavity height of 2.5 μm, and an optical wavelength of 10 μm;

[0071] Figure 26A It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the optical wavelength for seven different pixel fill factors under the conditions of a pixel pitch of 8.5 μm and a Fabry - Perot cavity height of 2.5 μm;

[0072] Figures 26B to 26G It is a graph showing the functional relationship between the absorption rate of the absorption layer of a microbolometer pixel and the optical wavelength for seven different pixel fill factors, where Figure 26B and 26C correspond to a Fabry - Perot cavity height of 2.5 μm and pixel pitches of 6 μm and 9 μm respectively; Figure 26D and 26E correspond to a Fabry - Perot cavity height of 1.5 μm and pixel pitches of 3.6 μm and 5.4 μm respectively; Figure 26F and26G corresponding to a Fabry - Perot cavity height of 5 μm and pixel pitches of 12 μm and 18 μm respectively;

[0073] Figures 26H to 26R is a graph showing the absorption rate of the absorption layer of a microbolometer pixel with a Fabry - Perot cavity height of 2.5 μm as a function of optical wavelength for seven different pixel fill factors, where the graphs respectively show examples with pixel pitches of 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, and 10 μm;

[0074] Figure 27 is a graph showing the ratio of non - absorbed diffracted power as a function of optical wavelength for seven different pixel fill factors, a pixel pitch of 8.5 μm, and a Fabry - Perot cavity height of 2.5 μm;

[0075] Figure 28 and 29 are graphs respectively showing the spatial distributions of the electric field and magnetic field in a microbolometer pixel with an absorption layer thickness of 6 nm, a pixel fill factor of 0.3, and an optical wavelength of 6 μm;

[0076] Figure 30 and Figure 31 are graphs respectively showing the spatial distributions of the electric field and magnetic field in a microbolometer pixel with an absorption layer thickness of 6 nm, a pixel fill factor of 0.3, and an optical wavelength of 8 μm;

[0077] Figure 32 and 33 are graphs respectively showing the spatial distributions of the electric field and magnetic field in a microbolometer pixel with an absorption layer thickness of 6 nm, a pixel fill factor of 0.3, and an optical wavelength of 10 μm;

[0078] Figure 34 and Figure 35 are graphs respectively showing the spatial distributions of the electric field and magnetic field in a microbolometer pixel with an absorption layer thickness of 6 nm, a pixel fill factor of 0.3, and an optical wavelength of 12 μm;

[0079] Figure 36 and Figure 37 are graphs respectively showing the spatial distributions of the electric field and magnetic field in a microbolometer pixel with an absorption layer thickness of 6 nm, a pixel fill factor of 0.3, and an optical wavelength of 14 μm;

[0080] Figure 38 and 39are diagrams respectively showing the spatial distributions of the electric and magnetic fields in a microbolometer pixel having an absorption layer with a thickness of 22 nm, a pixel fill factor of 0.3, and for a light wavelength of 6 μm;

[0081] Figure 40 and 41 are diagrams respectively showing the spatial distributions of the electric and magnetic fields in a microbolometer pixel having an absorption layer with a thickness of 22 nm, a pixel fill factor of 0.3, and for a light wavelength of 8 μm;

[0082] Figure 42 and Figure 43 are diagrams respectively showing the spatial distributions of the electric and magnetic fields in a microbolometer pixel having an absorption layer with a thickness of 22 nm, a pixel fill factor of 0.3, and for a light wavelength of 10 μm;

[0083] Figure 44 and Figure 45 are diagrams respectively showing the spatial distributions of the electric and magnetic fields in a microbolometer pixel having an absorption layer with a thickness of 22 nm, a pixel fill factor of 0.3, and for a light wavelength of 12 μm; and

[0084] Figure 46 and 47 are diagrams respectively showing the spatial distributions of the electric and magnetic fields in a microbolometer pixel having an absorption layer with a thickness of 22 nm, a pixel fill factor of 0.3, and for a light wavelength of 14 μm. DETAILED DESCRIPTION

[0085] Similar features have been designated by like references in the various figures. In particular, structural and / or functional features common to the various embodiments may have the same reference, and may be configured with the same structure, dimensions, and material properties.

[0086] For clarity, only the operations and elements that contribute to an understanding of the embodiments described herein have been described in detail. In particular, the circuitry for measuring the pixel resistance in a microbolometer array has not been described in detail, and the method for processing the captured pixel data to generate a thermal image has also not been described in detail.

[0087] In the following disclosure, unless otherwise specified, when referring to absolute position determiners such as the terms "front", "rear", "upper", "lower", "left", "right", etc., or relative position determiners such as the terms "above", "below", "higher than", "lower than", etc., or orientation determiners such as "horizontal", "vertical", etc., i.e., referring to the directions shown in the figures, or to the microbolometer oriented during normal use.

[0088] Unless otherwise specified, "about", "approximate", "substantially", and "circa" mean within 10%, and preferably within 5%.

[0089] In the following description, the following terms will be considered to have the following definitions.

[0090] "Absorption layer": The layer that absorbs energy from infrared light in the pixels of a microbolometer. In embodiments of the present disclosure, this layer is formed of a metal such as titanium nitride (TiN), titanium (Ti), or platinum (Pt).

[0091] "Pixel fill factor": The ratio between the surface area of the absorption layer and the surface area of the pixel. In the present disclosure, the value of the pixel fill factor is set with a precision of two decimal places.

[0092] "Pixel pitch" or "detection unit pitch": The spacing at which pixels / detection units are formed in a microbolometer array. The pixel pitch can correspond to the width of each pixel or detection unit in the x or y direction, or the distance from the edge of one pixel or detection unit to the corresponding edge of an adjacent pixel or detection unit. In the present disclosure, the pitch of pixels and detection units is set in micrometers with a precision of one decimal place, and in some cases two decimal places.

[0093] In the present disclosure, it is assumed that the value of sheet resistance is accurate to within 5%, and that the thickness expressed in nanometers is accurate to the nearest nanometer.

[0094] [[ID=5l]]Figure 1 An image capture device 100 of an infrared camera according to an exemplary embodiment is schematically shown. The device 100 includes an array 102 of pixels 104 that form a microbolometer capable of operating at ambient temperature. For example, the array includes N columns and M rows, where N and M are, for example, each equal to 2 or greater, and can be equal to 1000 or more. The output of the array 102 is coupled to a readout circuit 106, which is, for example, a readout integrated circuit (ROIC). For example, the circuit 106 includes one or more analog-to-digital converters for converting the signals captured in the microbolometer array 102 into a digital signal S. For example, the digital signal S is provided to a processing device (P) 108, which performs processing of the raw image data to generate a thermal image I. For example, the device 100 is capable of capturing a still thermal image or forming a video stream of thermal images.

[0095] Figure 2 is Figure 1A more detailed cross-sectional view of one of the pixels 104 of the microbolometer array 102. Pixel 104 includes a membrane 202 that is suspended over a reflective surface 204 formed on a substrate 206. For example, the membrane 202 is supported by arms 208 that also provide thermal insulation between the substrate 206 and the membrane 202.

[0096] For example, the membrane 202 includes an absorption layer 210, a thermal layer 212, and a dielectric layer 214 across at least a portion of its surface area, where one isolates the absorption layer and the thermal layers 210, 212 from each other, and the other two sandwich the layers 210, 212 therebetween.

[0097] The absorption layer 210 is formed of a metal such as titanium nitride, titanium, platinum, or other metals, for example. The absorption layer 210 absorbs the energy from the infrared light impinging on the pixel and is thus heated. This heat is transferred to the thermal layer 212, which is formed of a material having a resistance that varies with temperature. Contacts C1 and C2 near the edge of the thermal layer 212 allow the resistance of the thermal layer of each pixel to be measured via the readout circuit ( Figure 2 not shown in) via the arms 208.

[0098] The thickness Em of the membrane 202 is typically in the range of 100 nm to 1 μm.

[0099] The space between the surface of the membrane 202 and the reflective layer 204 defines a quarter-wavelength resonator 216, also known as a Fabry - Perot cavity. Typically, the resonator 216 is filled with air or under partial vacuum. The height h of the resonator is selected to achieve a relatively high absorption of infrared light by the absorption layer 210 of the membrane 202 over a desired wavelength range. In particular, the height h of the resonator is selected to be equal to λtg / 4, where λtg is the target wavelength.

[0100] The height h is, for example, in the range of 0.50 to 5.0 μm and, in some embodiments, in the range of 1.5 to 3.5 μm. Hereinafter, unless otherwise specified, the examples and simulations are based on a cavity height of 2.5 μm, which provides a relatively high absorption for light wavelengths centered around 10 μm. In fact, the spectrum near this wavelength is typically of most interest for thermal infrared applications. However, in alternative embodiments, different wavelengths of light may be targeted.

[0101] Figure 3 A portion of the microbolometer array 102 is shown in more detail according to an example embodiment. In Figure 1 this, the dashed grid represents the boundaries of the pixels of the array, and the solid rectangles represent the surface areas of the absorption layers 210 of each pixel. Figure 3

[0102] Figure 3 ​The x-axis therein is defined as corresponding to the direction of the pixel rows in the plane of the microbolometer array, and Figure 3 the y-axis therein is defined as corresponding to the direction of the pixel columns in the plane of the microbolometer array.

[0103] For example, the pixels in the microbolometer array have a pixel pitch Px in the x-direction and a pixel pitch Py in the y-direction, and the pixel pitches Px and Py are substantially the same, for example. Hereinafter, when referring to a specific value of the pixel pitch, unless otherwise stated, it is assumed to be the pitch in the x- and y-directions. The area Apix of the pixel is equal to Px·Py. The absorption layer 210 has, for example, a width Wx shorter than the pitch Px in the x-direction and a width Wy shorter than the pitch Py in the y-direction. Thus, the surface area Aabs of the absorption layer is equal to Wx·Wy. The pixel fill factor FF of the absorption layer within each pixel can be defined as Aabs / Apix.

[0104] First aspect

[0105] To provide a relatively high absorptivity of the microbolometer and thus a high sensitivity, the fill factor FF is typically selected to be as close to 1 as possible, as now referenced Figure 4 as described.

[0106] Figure 4 is a graph showing the functional relationship between the absorption rate (ABSORPTION RATE) and the fill factor (FF) for eight different sheet resistances of an absorption layer formed of titanium nitride and for a microbolometer pixel having a pixel pitch of 17.0 μm for a light wavelength of 10 μm, such as Figures 1 to 3 pixel 104.

[0107] Corresponding to Figure 4 curves 401 to 408, the sheet resistances and the thicknesses of the titanium nitride absorption layer are shown in the following table:

[0108] [Table 1]

[0109]

[0110]

[0111] As can be seen from Figure 4 it, by using a relatively thin absorption layer with a thickness of 5 or 10 nm and a fill factor above 0.65, an absorption rate above 0.9 can be achieved. The best absorption rate can be obtained by using an absorption layer with a thickness of 5 nm and a fill factor close to 0.90. However, for pixels with a pitch of 17.0 μm, the achievable fill factor is typically around 0.60.

[0112] To reduce the size of a microbolometer array while maintaining the number of pixels, it is desirable to reduce the pixel pitch. However, it is difficult to achieve a reduction in pixel pitch without significantly reducing the fill factor. Additionally, Figure 4 the curves of

[0113] indicate that reducing the fill factor will result in a significant reduction in absorptivity, which is undesirable.

[0114] Reducing the sheet resistance of the absorption layer means increasing its thickness. For example, for an absorption layer of titanium nitride, to achieve a sheet resistance of less than 200 ohm / sq, its thickness is at least 10 nm, and to achieve a sheet resistance of less than 130 ohm / sq, its thickness is at least 15 nm.

[0115] This increase in the thickness of the absorption layer increases the heat conduction between the absorption layer and the substrate, resulting in poorer performance. In particular, referring to Figure 2 the pixels of Figure 5 increasing the thickness of layer 210 will increase the heat conduction via arm 208 to substrate 206, resulting in a decrease in sensitivity. A modified pixel with a relatively low fill factor and relatively low heat conduction to the substrate will now be described in more detail with reference to

[0116] Figure 5 is a perspective view of a pixel 500 of a microbolometer according to an example embodiment of the present disclosure.

[0117] Pixel 500 includes, for example, a membrane 502 suspended over a reflective layer 504 formed on a substrate 506.

[0118] Membrane 502 is supported, for example, by a pair of arms 518, 520 that are respectively anchored to two posts 508 formed at opposite corners of the pixel. Each post 508 includes a base portion 510 from which a strut 512 extends. The struts 512 of the two posts pass through respective ends 514, 516 of arms 518, 520 and into a cover 522. Arms 518, 520 connect the posts to membrane 502 and in particular provide the function of mechanically supporting membrane 502, between membrane 502 and an ROIC formed, for example, in substrate 506 ( Figure 5a function of providing an electrical connection between (not shown in the figure) and a function of providing thermal insulation between the film 502 and the substrate 506. To provide good thermal insulation, the arms 518, 520 are relatively long, for example, providing a relatively high thermal resistance. In fact, in Figure 5 In the example of, the arms 518, 520 extend parallel to and are separated from the opposite edges of the film 502, and are attached to the opposite corners of the film 502 via the connecting portion 524. Therefore, the arms 518, 520 extend substantially the length of one edge of the film 502, for example. In some embodiments, each of the arms 518, 520 has a length of at least 50% of the pixel pitch.

[0119] For example, the film 502 includes a stack 526 in a part of its surface area, which includes a thermal layer 528 and an absorption layer 530, and these layers are insulated from each other by a dielectric layer ( Figure 5 not shown in the figure). For example, the stack 526 occupies less than 75% of the surface area of the film 502, including the surfaces of the arms 518, 520. The region of the film 502 surrounding the stack 526 forms a support layer for the stack 526, and also provides an electrical connection between the points near the edge of the thermal layer 528 and the arms 518, 520, so that the resistance of the thermal layer 528 can be measured by the readout circuit. For example, Figure 5 The dashed lines in show a schematic diagram of the electrical connections 531, 532 extending from the arms 518, 520 to the opposite edges of the thermal layer 528, respectively. These electrical connections 531, 532 and the arms 518, 520 are formed of a metal layer of titanium nitride, titanium, platinum, or other metals, and they are sandwiched between dielectric layers formed of silicon nitride, silicon dioxide, silicon oxynitride, or other electrically insulating materials, for example.

[0120] Although in Figure 5 In the embodiment of, the absorption layer 530 is formed on the thermal layer 528, but in an alternative embodiment, this order can be reversed. For example, the absorption layer 530 is formed on the bottom surface of the film 502.

[0121] The resonant cavity 533 between the reflective layer 504 and the film 502 forms a quarter-wavelength resonant cavity with a height of h. In one example, the height h is 2.5 μm to target a light wavelength of about 10 μm, although in alternative embodiments, different heights in the range of 1.5 to 3.5 μm can be used to target different light wavelengths.

[0122] In Figure 5 In the example of, the film 502 is substantially square, but includes notches 534, 536 at the opposite corners, thus leaving space for the posts 508. The stack 526 is formed, for example, in a part of the film 502 between these notches, thus extending to almost the full length of the film 502.

[0123] Of course, althoughFigure 5 An embodiment of a bolometer with an absorber layer having a relatively low sheet resistance is provided, but many different embodiments will be apparent to those skilled in the art, such as omitting the base portion 510 and / or the cover 522, and / or using different forms of the arms 518, 520 and the electrical connections 531, 532.

[0124] Figure 6 is a cross-sectional view taken along Figure 5 line A-A' through the membrane 502 and the arms 518, 520.

[0125] As Figure 6 shown, the membrane 502 is formed, for example, of a dielectric layer 602, and the electrical connections 531, 532 are formed, for example, by metal deposition. The thermal layer 528 and the absorber layer 530 are electrically insulated from each other, for example, by a dielectric layer 604, and a region near the bottom edge of the thermal layer 528 is in contact, for example, with the top surface of the electrical connections 531, 532 and is otherwise covered by a dielectric material. In one embodiment, the absorber layer 530 is a titanium nitride layer having a thickness of at least 10 nm and in some cases at least 15 nm. For example, the thermal layer 528 has a thickness of approximately 100 nm.

[0126] It should be noted that although the electrical connections 531, 532 increase the absorption surface area of the pixel, the inventors have found that they have a relatively small effect on the effective optical fill factor of the pixel and can therefore be ignored, given the relatively low thickness and high sheet resistance of these metal layers.

[0127] Figure 7 is a graph showing the functional relationship between the absorption rate (ABSORPTIONRATE) of the absorber layer and the fill factor (FF) of a bolometer pixel (such as Figure 5 pixel 500) for eight different sheet resistances of the absorber layer 530, and having a pitch of 8.5 μm. As in Figure 4 the example of Figure 7 is based on a quarter-wavelength resonator having a height of 2.5 μm and a light wavelength of 10 μm. It is assumed that the absorber layer 530 is formed of titanium nitride, and Figure 7 the sheet resistances of the absorber layer 530 corresponding to curves 701 to 708 are the same as those of curves 401 to 408 in Table 1, respectively.

[0128] From Figure 7 it can be seen that in the case of curves 702 to 708, the best absorption rate can be achieved when the fill factor is equal to 0.50 or lower, and in the case of curves 703 to 708, it can be achieved when the fill factor is 0.40 or lower.

[0129] From Figure 7It can be seen that when the fill factor is below 0.20, the absorption rate drops rapidly, even for the thickest absorption layer. Thus, in some embodiments, the fill factor can be selected to be equal to or greater than 0.20.

[0130] Thus, from Figure 7 It can be seen that by reducing the fill factor of the absorption layer of each pixel to a range of 0.1 to 0.5 and also reducing the sheet resistance of the absorption layer to less than 189 ohm / sq, and in some embodiments less than 130 ohm / sq, a microbolometer with a relatively low pixel pitch and high absorption rate can be achieved.

[0131] Now reference will be made to Figure 8 and Figure 9 to describe in more detail an example of a microbolometer array having a fill factor of 0.5 or less.

[0132] Figure 8 FIG. shows a portion of a microbolometer array 800 according to an example embodiment. Similar to Figure 3 , the dashed grid represents the boundaries of the pixels 804 of the array, and the solid rectangles represent the surface areas of each absorption layer 530. However, with respect to the example of Figure 3 , the pixel fill factor FF has been reduced in the array of Figure 8 , for example, to a value in the range of 0.10 to 0.50. Additionally, in Figure 8 , the absorption layer 530 is not square but rectangular, with the width Wx on the x-axis being less than the width Wy on the y-axis. The pixels are, for example, square, with the pixel pitch Px in the x-direction equal to the pixel pitch Py in the y-direction, although in some embodiments these pitches can be different. For example, the pitches Px and Py are each in the range of 5.0 to 11.0 μm.

[0133] In the example of Figure 8 , each pixel 804 of the array corresponds to a detection unit including a single absorption layer 530. In alternative embodiments, each pixel can include more than one detection unit, as will now be described in connection with Figure 9 .

[0134] Figure 9 FIG. shows a portion of a microbolometer array 900 of a microbolometer according to another example embodiment. In the example of Figure 9 , the dashed grid represents the boundaries of the pixels 904 of the array, and the solid rectangles represent the surface areas of the absorption layers 530. Each pixel 904 includes more than one detection unit, and each detection unit has a corresponding absorption layer 530. In Figure 9In the example of, each pixel 904 includes four detection units arranged in a two-by-two configuration. The detection units of each pixel 904 are coupled together, for example, such that they generate a single pixel value, and thus each set of detection units can be considered to form a single pixel of the array.

[0135] In Figure 9 the case of, the pixel fill factor FF becomes equal to the ratio Aabs / Apix, where Apix is the surface area of each pixel, and Aabs is the combined surface area of the absorption layer 530 in each pixel.

[0136] In Figure 9 the case of, the relevant spacing is no longer the pixel spacing, but the spacing of the detection units, that is, the spacing of the absorption layer 530. In Figure 9 these spacings are labeled Px and Py in the x and y directions, respectively. For example, these spacings Px, Py are measured from the edge of one absorption layer 530 to the corresponding edge of the adjacent absorption layer 530.

[0137] Figure 10 is similar to Figure 7 the graph of, for the same type of microbolometer pixel, but further shows the curve where the sheet resistance drops to 16 ohm / sq. In fact, Figure 10 the curves 1001 to 1008 of represent absorption layers having the same sheet resistance as those of curves 401 to 408 in Table 1. Curves 1009 to 1023 correspond to the sheet resistance and titanium nitride thickness shown in the following table.

[0138] [Table 2]

[0139] Reference curve Titanium nitride thickness (nm) Sheet resistance (ohm / sq) 1009 45 42 1010 50 38 1011 55 34 1012 60 31 1013 65 29 1014 70 27 1015 75 25 1016 80 24 1017 85 22 1018 90 21 1019 95 20 1020 100 19 1021 105 18 1022 110 17 1023 115 16

[0140] From Figure 10 it can be seen that providing microbolometer pixels having a fill factor between 0.10 and 0.50 and a sheet resistance between 16 and 189 ohm / sq can significantly reduce the pixel spacing (down to 8.5 μm in the Figure 10 example of), while achieving an absorption rate of at least 0.3, or at least 0.45 in the case where the sheet resistance is between 42 and 126 ohm / sq.

[0141] Furthermore, although a lower sheet resistance level of less than 50 ohm / sq may not achieve an absorption rate close to 1.0, for fill factors between 0.10 and 0.30, they can provide a significant gain in using an absorption layer corresponding to curve 1001 having a sheet resistance close to 377 ohm / sq, which will now be explained in more detail with reference to Figures 11 to 13 more specifically.

[0142] Figure 11 is a graph showing curves 1102 to 1135, which represent the gain in terms of absorption relative to the absorption layer represented by curve 1001 in ​ . In particular, ​ curves 1102 to 1123 of ​ represent the gain of the absorption layer corresponding to curves 1002 to 1023 of ​ . Curves 1124 to 1135 in ​ represent absorption layers with thicknesses increasing in 5 nm increments from 120 to 190 nm. Curves 1126 to 1134 are not labeled in

[0143] but can be easily identified by their order between curves 1125 and 1135. ​ As can be seen from

[0144] - the pixel fill factor is equal to or greater than 0.40 and less than 0.50, and the sheet resistance is between 75 and 189 ohm / sq; or

[0145] - the pixel fill factor is equal to or greater than 0.30 and less than 0.40, and the sheet resistance is between 47 and 189 ohm / sq; or

[0146] - the pixel fill factor is equal to or greater than 0.20 and less than 0.30, and the sheet resistance is between 25 and 189 ohm / sq; or

[0147] - the pixel fill factor is equal to or greater than 0.10 and less than 0.20, and the sheet resistance is between 16 and 189 ohm / square.

[0148] ​ Curves 1102 to 1125 of ​ are described in more detail, and in particular a gain of 20% or more. As can be seen from ​ a gain of more than 20% can be achieved in any of the following cases:

[0149] - the pixel fill factor is equal to or greater than 0.30 and less than 0.40, and the sheet resistance is between 94 and 189 ohm / sq; or

[0150] - the pixel fill factor is equal to or greater than 0.20 and less than 0.30, and the sheet resistance is between 38 and 189 ohm / sq; or

[0151] - the pixel fill factor is equal to or greater than 0.10 and less than 0.25, and the sheet resistance is between 22 and 189 ohm / sq.

[0152] ​is described in more detail ​ curves 1102 to 1115, and in particular a gain of 50% or more. From ​ it can be seen that when the pixel fill factor is equal to or greater than 0.10 and less than 0.24, and the sheet resistance is between 34 and 189 ohm / sq, a gain of more than 50% can be achieved.

[0153] ​ represents, for a fill factor of 0.10 (curve 1401) and 0.20 to 0.90 (curves 1402 to 1409, ​ only curves 1402 and 1409 are labeled in), the functional relationship of the absorption rate to the ratio of the sheet resistance (Rs) to the fill factor (FF). As in the previous example, ​ the curves correspond to an absorption layer formed of titanium nitride, having a pixel pitch of 8.5 μm, a quarter-wavelength resonator height of 2.5 μm, and a light wavelength of 10 μm.

[0154] ​ is described in more detail for curves 1402 to 1409 in ​ where the absorption rate is greater than or equal to 0.90. It can be seen that when the fill factor is between 0.10 and 0.50, and the ratio Rs / FF is in the range of 200 to 600 ohm / sq, an absorption rate of more than 0.90 can be achieved. From ​ it can also be noted that the curves are basically centered around a ratio of 377 ohm / sq, where 377 ohm corresponds to the impedance of free space Z0. In fact, for example, when the ratio Rs / FF is equal to 377 ± 40%, a high absorption rate of more than 0.93 can be observed, and when the ratio Rs / FF is equal to 377 ± 20%, an even higher absorption rate of more than 0.95 can be observed.

[0155] The above examples are based on a quarter-wavelength resonator height of 2.5 μm. The principles described in connection with these examples apply equally to different quarter-wavelength resonator heights, for example for a quarter-wavelength resonator height in the range of 1.5 to 3.5 μm, which will now be explained with reference to ​ and ​

[0156] ​ represents, for eight different sheet resistances of the absorption layer 530 and for a light wavelength of 13 μm, and having a pitch of 11 μm and a quarter-wavelength resonator height of 1.5 μm, the absorption rate (ABSORPTION RATE) versus microbolometer pixels such as ​ ​The graph of the functional relationship of the fill factor (FF) of the pixel 500). It is assumed that the absorption layer 530 is formed of titanium nitride, and the sheet resistance of the absorption layer 530 (corresponding to ​ The sheet resistances of curves 1601 to 1608) are the same as those of curves 401 to 408 in Table 1, respectively.

[0157] From ​ it can be seen that the result is similar to ​ the result of

[0158] ​ This is a graph showing the functional relationship between the absorption rate and the fill factor (FF) of microbolometer pixels (such as ​ the pixel 500) for eight different sheet resistances of the absorption layer 530, a light wavelength of 6 μm, a pitch of 5 μm, and a quarter-wavelength resonator height of 1.5 μm. It is assumed that the absorption layer 530 is formed of titanium nitride, and the sheet resistance of the absorption layer 530 (corresponding to ​ the curves 1701 to 1708) are the same as those of curves 401 to 408 in Table 1, respectively.

[0159] From ​ it can be seen that the gain shown by curves 1702 to 1708 with respect to curve 1701 is more significant for fill factors in the range of 0.10 to 0.50, but the best results can be obtained when the sheet resistance is less than 75 ohm / sq.

[0160] More generally, the principles described herein apply, for example, to any pixel pitch in the range of 5 to 11 μm, where the quarter-wavelength resonator height is, for example, equal to λtg / 4, where λtg is the light wavelength of interest (target wavelength), and the pitch is less than λtg. Thus, in the case of a quarter-wavelength resonator height of 1.5 μm, the pixel pitch is, for example, less than 6 μm, and in the case of a quarter-wavelength resonator height of 3.5 μm, the pixel pitch is, for example, anywhere in the range of 5 to 11 μm.

[0161] ​ and ​ the results of ​ are based on pixels with a pitch of 8.5 μm. The principles described with respect to these examples can be applied to pixels with a pitch at any position in the range of 5 to 11 μm, as will be described in more detail now with reference to

[0162] ​It shows the absorption rate as a function of the fill factor (FF) of microbolometer pixels (such as ​ pixel 500) for eight different sheet resistances of the absorption layer 530, with a quarter-wavelength resonator height of 2.5 μm and an optical wavelength of 10 μm. It is assumed that the absorption layer 530 is formed of titanium nitride, and the sheet resistances of the absorption layer 530 corresponding to ​ curves i01 to i08 (for i from 18 to 25) are the same as those of curves 401 to 408 in Table 1, respectively.

[0163] ​ Figure shows an example with a pixel pitch of 5 μm, ​ is an example with a pixel pitch of 6 μm, ​ is an example with a pixel pitch of 7 μm, ​ is an example with a pixel pitch of 8 μm, [[ID=1⑤]] ​ is an example with a pixel pitch of 9 μm, ​ is an example with a pixel pitch of 10 μm, ​ is an example with a pixel pitch of 11 μm, and ​ is an example with a pixel pitch of 12 μm.

[0164] As ​ shown, for pixel pitches from 5 to 6 μm and fill factors from 0.10 to 0.40, the best results are obtained when the sheet resistance is between 94 and 189 ohm / sq; for pixel pitches from 6 to 7 μm and fill factors from 0.10 to 0.50, the best results are obtained when the sheet resistance is between 94 and 189 ohm / sq, and for pixel pitches from 7 to ⑨ μm and fill factors from 0.10 to 0.50, the best results are obtained when the sheet resistance is between 75 and 189 ohm / sq.

[0165] As ​ shown, for pixel pitches from 9 to 10 μm and fill factors from 0.10 to 0.50, the best results can be obtained when the sheet resistance is between 75 and 189 ohm / sq, and for pixel pitches from 10 to less than 12 μm and fill factors from 0.10 to 0.50, the best results can be obtained when the sheet resistance is between 94 and 189 ohm / sq.

[0166] ​

[0167] Another difficulty with microbolometers is filtering out light of wavelengths outside the target range. In some embodiments, surface treatments and / or coatings may be applied to one or more optical elements between the microbolometer array and the image scene to filter the received light. However, these techniques increase the cost.

[0168] The present inventor has found that a certain choice of pixel pitch or detector element pitch can result in a filtering function, as now referenced ​ and ​ described.

[0169] ​ is a graph showing the absorption rate as a function of optical wavelength for a pixel pitch / detector element pitch of 8.5 μm and for seven different pixel fill factors of microbolometer pixels (such as ​ pixel 500). For each fill factor, the thickness of the absorption layer is selected such that the ratio Rs / FF is substantially equal to 377 ohm / sq. In particular, ​ the curves 2601 to 2607 in

[0170] [Table 3]

[0171]

[0172] From ​ it can be seen that, depending on the fill factor, in the wavelength range (RANGE λr) of approximately 6 to 8 μm, a filtering function with a cut-off frequency λr (defined as an absorption rate less than 0.5) is obtained. The present inventor has found that this filtering function is the result of diffraction that occurs when the pitch of the pixels or detector elements in any one or both of the x and y directions approaches the lower cut-off wavelength defined by a quarter-wavelength resonator of each pixel. In the ​ example, the height h of the quarter-wavelength resonator is 2.5 μm, resulting in a lower cut-off wavelength λc of approximately 6 μm. More generally, the lower cut-off wavelength λc defined by the quarter-wavelength resonator is equal to approximately 0.6λ0, where λ0 is equal to the target wavelength, which is equal to four times the height h of the quarter-wavelength resonator.

[0173] It should be noted that below the trough at approximately 6 μm, the absorption rate rises again, reaching a peak at a wavelength of approximately 4 μm. However, these lower wavelengths are removed, for example, by a relatively inexpensive surface treatment or filtering layer applied to the optical element between the microbolometer array and the image scene.

[0174] More generally, the height h of the quarter-wavelength resonator of each pixel (see, for example, ​ and ​ ) is in the range of 0.5 to 5 μm, resulting in a target optical wavelength between 2 and 20 μm. However, for a quarter-wavelength resonator of at least 1.5 μm (corresponding to a target optical wavelength of at least 6 μm), the filtering performance is particularly evident.

[0175] A quarter - wavelength resonator with a height of 1.5 μm results in a lower cut - off wavelength λc of about 3.6 μm, and a quarter - wavelength resonator with a height of 5 μm results in a lower cut - off wavelength λc of about 12 μm. In some embodiments, the height h of the quarter - wavelength resonator for each pixel is in the range of 1.5 to 3.5 μm.

[0176] For example, to obtain a filtering function, the detection unit pitch is selected in the range of 0.9λc to 1.65λc, corresponding to the range [1.2λ0 / 2–1.8λ0 / 2] ± 10%, and preferably from λc to 1.5λc. In fact, this corresponds to the range in which the quarter - wave cut - off frequency effect works. When the detection unit pitch is selected in the range of 2.4h to 3.6h, where h is the height of the quarter - wavelength resonator, the filtering performance is particularly obvious. Thus, for a quarter - wavelength resonator height of 2.5 μm, the pixel pitch is in the range of 6 to 9 μm. In some embodiments, according to a second aspect, the pitch of the detection units is between 3.6 μm and 18 μm, and for example between 4 μm and 15 μm, and preferably between 5 and 11 μm.

[0177] As can be seen from ​ it, as the fill factor decreases and the thickness of the absorption layer increases, the suppression, that is, the filtering, is enhanced. In some embodiments, the absorption layer is formed of a metal and has a sheet resistance Rs of less than 189 ohm / sq.

[0178] In some embodiments, the fill factor and the sheet resistance of the absorption layer are selected based on the same criteria as described above with respect to the first aspect. For example, the absorption layer has a pixel fill factor FF in the range of 0.10 to 0.50 and a sheet resistance Rs in the range of 16 to 189 ohm / sq. Additionally, to obtain a relatively high absorption gain, the absorption layer is selected such that:

[0179] - the pixel fill factor is equal to or greater than 0.40 and less than 0.50, and the sheet resistance is between 75 and 189 ohm / sq; or

[0180] - the pixel fill factor is equal to or greater than 0.30 and less than 0.40, and the sheet resistance is between 47 and 189 ohm / sq; or

[0181] - the pixel fill factor is equal to or greater than 0.20 and less than 0.30, and the sheet resistance is between 25 and 189 ohm / sq; or

[0182] - the pixel fill factor is equal to or greater than 0.10 and less than 0.20, and the sheet resistance is between 16 and 189 ohm / sq.

[0183] In addition, in some embodiments, the ratio Rs / FF is in the range of 200 to 600 ohm / sq, or in the range of 377 ± 40%, or even in the range of 377 ± 20%.

[0184] ​ is a graph showing the relationship of the ratio of non-absorbed diffracted power to the optical wavelength as a function thereof. ​ The seven curves 2701 to 2707 of ​ respectively correspond to the same absorption layers as the curves 2601 to 2607 of

[0185] Although ​ the graph of ​ shows some artifacts, such as negative power near a wavelength of 5 μm, the graph still represents the general behavior of the absorption layer.

[0186] In addition, ​ the graph of

[0187] ​ confirms that the filtering effect is enhanced as the fill factor decreases and the absorption layer thickness increases. ​ is a graph showing the relationship of the absorptance of the absorption layer of a microbolometer pixel to the optical wavelength for seven different pixel fill factors and absorption layer thicknesses that are the same as those of ​ where the corresponding curves are labeled with the same reference marks as

[0188] ​ and 26C correspond to a Fabry - Perot cavity height of 2.5 μm and pixel pitches of 6 μm and 9 μm respectively.

[0189] ​ and 26E correspond to a Fabry - Perot cavity height of 1.5 μm and pixel pitches of 3.6 μm and 5.4 μm respectively.

[0190] ​ and 26G correspond to a Fabry - Perot cavity height of 5 μm and pixel pitches of 12 μm and 18 μm respectively.

[0191] ​ is a graph showing for ​Graph of the absorption rate of the absorber layer of a microbolometer pixel with the same seven different pixel fill factors and absorber layer thicknesses, having a Fabry - Perot cavity height of 2.5 μm, as a function of the optical wavelength, where the corresponding curves are labeled with the same reference marks as in ​ the same. ​ Examples with pixel pitches of 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, and 10 μm are shown respectively, and it is demonstrated that when the pixel pitch is in the range of 2.4h to 3.6h, corresponding to the range of 6 μm to 9 μm, and especially when the fill factor is at least 0.2, the filtering function is particularly obvious.

[0192] It should be noted that if a graph is plotted similar to ​ but with a quarter - wavelength resonator height of 1.5 μm, 5 μm, or anywhere in between, similar curves will be obtained, but the x - axis is scaled in view of the target wavelength.

[0193] ​

[0194] ​ is a graph showing the spatial distribution of the electric and magnetic fields in a pixel (such as pixel 104 or 500 above) with a pixel pitch of 8.5 μm and a quarter - wavelength resonator height h of 2.5 μm. Also refer to ​ , in ​ the vertical scale shown in the figure, the reflective layer 204 is located at approximately 0 μm, and the absorber layer 210 is located at approximately 2.5 μm.

[0195] For example, the electric field is represented by contour lines corresponding to the electric field strength in V / m in the figure. For example, the magnetic field is represented by contour lines associated with the magnetic field strength in A / m in the figure.

[0196] ​ The curves of ​ and 29 show the spatial distribution of the electric and magnetic fields in a pixel of a microbolometer having an absorber layer thickness of 6 nm and a pixel fill factor of 0.30. In these figures, ​ and 31 represent the electric and magnetic field distributions in the case of light with a wavelength of 6 μm respectively, ​ and 33 represent the electric and magnetic field distributions in the case of light with a wavelength of 8 μm respectively, ​ and ​ represent the electric and magnetic field distributions in the case of light with a wavelength of 10 μm respectively, and ​and ​ respectively represent the electric field and magnetic field distributions in the case of light with a wavelength of 14 μm.

[0197] ​ The curves of ​ show the spatial distributions of the electric and magnetic fields in the pixels of a microbolometer having an absorption layer 22 nm thick and a pixel fill factor of 0.30. In these figures, ​ and 39 respectively represent the electric field and magnetic field distributions in the case of light with a wavelength of 6 μm, ​ and 41 respectively represent the electric field and magnetic field distributions in the case of light with a wavelength of 8 μm, ​ and ​ respectively represent the electric field and magnetic field distributions in the case of light with a wavelength of 10 μm, ​ and ​ respectively represent the electric field and magnetic field distributions in the case of light with a wavelength of 12 μm, and ​ and ​ respectively represent the electric field and magnetic field distributions in the case of light with a wavelength of 14 μm.

[0198] It can be seen that at a light wavelength of 6 μm ( ​ , 29 , 38 and 39), the Fabry - Perot cavity effect dominates, while in the case of a relatively thick absorption layer ( ​ and 39 ), there are diffraction effects, resulting in a highly dispersed field strength.

[0199] For light with a wavelength of 8 μm ( ​ , 31 , 40 and 41), the diffraction effect dominates, especially for a relatively thick absorption layer ( ​ and 41 ). This phenomenon is also amplified when the fill factor decreases. In addition, for a relatively thick absorption layer, the field strength is strongly amplified.

[0200] For light with wavelengths of 10 μm, 12 μm, and 14 μm, in the case of a relatively thin absorption layer ( ​ ), the Fabry - Perot coupling dominates, while for a thicker absorption layer ( ​ ), the Fabry - Perot coupling is replaced by phenomena characterized by the concentration of the electric field at the edges of the absorption layer and the confinement of the magnetic field below the absorption layer.

[0201] An advantage of the embodiments related to the first aspect described herein is that a relatively high absorption rate can be achieved when using a relatively compact microbolometer array.

[0202] An advantage of the embodiments related to the second aspect described herein is that a filtering function can be obtained, thereby relaxing the constraints on the optical filter of the microbolometer.

[0203] In addition, based on simulations performed on absorption layers with thicknesses of 6 and 18 nm, the inventors have found that a reduction in the pixel fill factor to the range of 0.10 to 0.50 and an increase in the absorption layer thickness do not result in an increase in crosstalk between pixels.

[0204] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these embodiments can be combined, and those skilled in the art will readily come up with ideas for other variations. For example, it will be obvious to those skilled in the art that although examples of absorption layers formed of titanium nitride have been described in detail, the principles described herein can be applied to other materials, including different metals.

Claims

1. A microbolometer comprising a pixel array, each pixel including one or more detection units, each detection unit including an absorption layer (210, 530), wherein: - the pitch of the detection units in at least one direction in the pixel array plane is between 5 and 11 μm; - the pixel fill factor FF of the absorption layer (530) of the one or more detection units in each pixel is in the range of 0.10 to 0.50; and - the sheet resistance Rs of the absorption layer (530) of each detection unit is between 20 and 189 ohm / sq, and the ratio Rs / FF of each pixel of the array is between 200 and 600 ohm / sq.

2. The microbolometer according to claim 1, wherein, Each pixel has a pixel fill factor in the range of 0.10 to 0.

40.

3. The microbolometer according to claim 1, wherein, Each pixel has a pixel fill factor in the range of 0.20 to 0.

40.

4. The microbolometer according to any one of claims 1 to 3, wherein, The pitch of the detection units in at least one direction in the pixel array plane is between 8 and 9 μm.

5. The microbolometer according to claim 4, wherein, Each pixel of the array has: - a pixel fill factor FF equal to or greater than 0.40 and less than 0.50, and the sheet resistance Rs of the absorption layer (530) is at least 75 ohm / sq; or - a pixel fill factor FF equal to or greater than 0.30 and less than 0.40, and the sheet resistance Rs of the absorption layer (530) is at least 50 ohm / sq; or - a pixel fill factor FF equal to or greater than 0.20 and less than 0.30, and the sheet resistance Rs of the absorption layer (530) is at least 25 ohm / sq; or - a pixel fill factor FF equal to or greater than 0.10 and less than 0.20, and the sheet resistance Rs of the absorption layer (530) is at least 20 ohm / sq.

6. The microbolometer according to any one of claims 1 to 3, wherein, The ratio Rs / FF is in the range of 377 ohm / sq ± 20%.

7. The microbolometer according to any one of claims 1 to 3, wherein, The absorption layer (530) of each detection unit is a metal layer.

8. The microbolometer according to claim 7, wherein, The absorption layer (530) is formed of TiN and has a thickness between 10 and 115 nm.

9. The microbolometer according to any one of claims 1 to 3, wherein, The pixel array includes a substrate (506), and each pixel of the pixel array includes: a reflective layer (504) formed on the substrate (506) and a film (502) suspended on the reflective layer (504), a quarter-wavelength resonator (533) is formed between the film (502) and the reflective layer (504) in each pixel, and the film (502) includes the absorption layer (530) and a thermal layer (528).

10. The microbolometer according to claim 9, wherein, The absorption layer (530) has a surface area less than 75% of the surface area of the film (502).

11. The microbolometer according to claim 9, wherein, The quarter-wavelength resonator (533) has a height (h) in the range of 1.5 to 3.5 μm.

12. The microbolometer according to claim 11, wherein, The pitch of the detection units in at least one direction in the pixel array plane is less than four times the height (h) of the quarter-wavelength resonator (533).

13. A method of manufacturing a microbolometer array, comprising: - forming a pixel array, each pixel having one or more detection units, wherein forming the array includes: - Form the detection unit such that it has a pitch between 5 and 11 μm on at least one axis in the plane of the pixel array; and - Form each detection unit to include an absorption layer (210, 530) having a pixel fill factor FF in the range of 0.10 to 0.50 and a sheet resistance Rs between 20 and 189 ohm / sq, and the ratio Rs / FF of each pixel of the array is between 200 and 600 ohm / sq.

Images