DE102017012296B4 - infrared radiation sensors - Google Patents

Abstract

An infrared radiation sensor, comprising:a substrate (24, 120) having a major surface defining a substrate plane;a diaphragm (10, 110) formed in or on the substrate (24, 120), at least a portion the membrane (10, 110) forms a deflectable electrode; anda counter electrode (116, 116a, 116b);wherein the deflectable electrode and the counter electrode (116, 116a,116b) face each other laterally with respect to the substrate plane, wherein between the deflectable electrode and the counter electrode (116, 116a, 116b) a capacitance is formed, wherein the membrane (10, 110) comprises a composition comprising at least two layers (12, 14, 112, 114) of materials having different coefficients of thermal expansion, and wherein the composition comprises an absorption region configured to, by absorbing infrared radiation to cause a deformation of the composition, which deformation leads to a vertical deflection, with respect to the substrate plane, of the deflectable electrode relative to the counter electrode (116, 116a, 116b), which causes a change in capacitance, the counter electrode (116, 116a , 116b) facing the deflectable electrode at a plurality of lateral edges of the deflectable electrode, wobe i a membrane support (130) is coupled to the membrane (110) in a region spaced from lateral edges of the membrane (110) as seen in a plan view of the substrate plane, and wherein the membrane support (130) is coupled to the membrane (110) is coupled in a central region of the membrane (110), in a plan view of the substrate plane.

Description

Area

The present disclosure relates to infrared radiation sensors and methods of making infrared radiation sensors. More particularly, the present disclosure relates to microelectromechanical systems (MEMS) infrared radiation sensors and methods of fabricating infrared radiation sensors and using MEMS technologies.

background

Infrared imaging is used in a variety of well-known industrial, commercial, and military applications such as security, law enforcement, and industrial and environmental monitoring. The ability to detect infrared radiation enables a wide range of applications, from temperature measurements to accurate characterization of all types of inorganic and organic substances by spectroscopic methods such as IR and Raman spectroscopy.

In infrared cameras, bolometers can be used as radiation detectors. In such bolometers, detection takes place indirectly by converting absorbed light energy into heat. The heat leads to an intensification of the scattering of freely movable electrons within a solid body. Therefore, an increase in electrical resistance can be detected as a signal. Highly doped silicon, both amorphous and polycrystalline in the form of a membrane can be used as a heat-sensitive resistive element. The surface area and thickness of the membrane can be adjusted or optimized to achieve maximum efficient radiation reception. Bolometers can have a pixel size of 17×17 μm ² and a thermal contrast (NETD=Noise Equivalent Temperature Difference) of 30 mK to 50 mK.

Generally, bolometers can have two electrical contacts connected to the membrane on two opposite sides thereof to operate the membrane structure as a resistor. This can result in relatively high heat dissipation through the contact structures, which can be implemented using metal studs, and therefore sensitivity can be reduced. Miniaturization of the bolometers is directly related to a reduction in the active surface area of the membrane.

Other infrared imagers can use differential capacitive MEMS infrared sensors within a sensor array. Such differential capacitive infrared sensors may include a bi-material deflectable electrode element anchored to a top surface of an integrated circuit substrate and a surface electrode fabricated on the top surface of the integrated circuit substrate and positioned below the deflectable electrode element. The surface electrode and the deflectable electrode element may be separated by a gap to form a first variable capacitor having a first capacitance value. An infrared transmissive sealing lid electrode may also be provided. A first bias may be applied to the surface electrode and a second bias may be applied to the sealing cap electrode. A differential capacitance monitor is physically coupled to the bi-material deflectable electrode member, the surface electrode, and the sealing cap electrode. The differential capacitance monitor is operable to monitor an amount of differential between the first capacitance value of the first adjustable capacitor and the second capacitance value of the second adjustable capacitor.

Infrared capacitance sensors may consist of a bi-material strip that changes the position of one plate of a sensing capacitor in response to temperature changes due to absorbed incident thermal radiation. The bi-material strip may be composed of two materials with a large difference in thermal expansion coefficients. The plates of the sense capacitor face each other parallel to a substrate plane and are electrically connected to a sense circuit.

From the U.S. 2010/0 243 904 A1 an infrared sensor is known in which a cantilever beam provided with a functional layer is laterally opposed to a cantilever beam not provided with a functional layer. When infrared radiation is absorbed, the functional layer causes the corresponding cantilever beam to be deflected, which in turn can be detected by a change in capacitance.

the U.S. 6,737,648 B2 shows an infrared sensor in which a movable electrode and a stationary electrode face each other laterally with respect to a substrate plane. A deflection of the movable electrode takes place parallel to the substrate plane.

abstract

The present invention provides an infrared radiation sensor according to claim 1 and an infrared radiation sensor according to claim 2. Further developments of the invention are defined in the dependent claims. Examples of the present disclosure that do not fall under the scope of the claims do not form part of the invention and are provided for illustrative purposes only.

character list

• 1a bis 1c zeigen schematische Querschnittsansichten zum Erläutern von Beispielen von nicht erfindungsgemäßen Infrarotstrahlungssensoren mit Elektroden, die einander in einer seitlichen Richtung zugewandt sind;
• 2a und 2b zeigen eine schematische Draufsicht und eine schematische Querschnittsansicht eines Beispiels eines erfindungsgemäßen Infrarotstrahlungssensors mit Elektroden, die einander in einer zeitlichen Richtung zugewandt sind, und einer zentral getragenen Membran;
• 3a und 3b zeigen eine schematische Draufsicht und eine schematische Querschnittsansicht eines weiteren Beispiels eines erfindungsgemäßen Infrarotstrahlungssensors mit Elektroden, die einander in einer seitlichen Richtung zugewandt sind, und einer zentral getragenen Membran;
• 4 zeigt eine Modifikation des Sensors von 3b;
• 5 zeigt eine schematische Querschnittsansicht eines Beispiels eines erfindungsgemäßen Infrarotstrahlungssensors, der zwei Gegenelektroden und eine floatende ablenkbare Elektrode aufweist;
• 6 zeigt eine schematische Querschnittsansicht eines Beispiels eines nicht erfindungsgemäßen Infrarotstrahlungssensors mit vertikaler Auslesung;
• 7 zeigt eine schematische Querschnittsansicht eines weiteren Beispiels eines nicht erfindungsgemäßen Infrarotstrahlungssensors mit vertikaler Auslesung;
• 8 zeigt eine schematische Querschnittsansicht eines Beispiels eines nicht erfindungsgemäßen Infrarotstrahlungssensors, der Gegenelektroden aufweist, die in einem Deckel des Sensors gebildet sind;
• 9 zeigt eine schematische Draufsicht von Abschnitten des Substrats des Sensors, der in 8 gezeigt ist;
• 10 zeigt eine schematische dreidimensionale Ansicht von Abschnitten des Sensors von 8 und 9, wobei Abschnitte abgeschnitten sind;
• 11 zeigt eine schematische Ansicht einer Membran und Tragestrukturen des in 8 gezeigten Sensors;
• 12a bis 12c zeigen schematische Querschnittsansichten, die unterschiedliche Betriebszustände des Sensors von 8 zeigen;
• 13a und 13b zeigen Ersatzschaltungen eines Sensors, wie er in 8 gezeigt ist;
• 14a und 14b zeigen eine schematische Ansicht und eine Ersatzschaltung zum Erläutern eines Beispiels einer Erfassungsschaltung;
• 15a und 15b zeigen eine schematische Ansicht und eine Ersatzschaltung zum Erläutern eines weiteren Beispiels einer Erfassungsschaltung;
• 16a und 16b zeigen eine schematische Ansicht und eine Ersatzschaltung zum Erläutern noch eines weiteren Beispiels einer Erfassungsschaltung;
• 17a bis 17l zeigen schematische Querschnittsansichten von Schritten von Beispielen von Verfahren zum Herstellen von Infrarotstrahlungssensoren.

Examples of the disclosure will be described using the accompanying drawings.

• 1a until 1c Fig. 12 shows schematic cross-sectional views for explaining examples of infrared ray sensors not according to the invention having electrodes facing each other in a lateral direction;
• 2a and 2 B Fig. 12 shows a schematic plan view and a schematic cross-sectional view of an example of an infrared radiation sensor according to the invention having electrodes facing each other in a temporal direction and a centrally supported diaphragm;
• 3a and 3b Fig. 12 shows a schematic plan view and a schematic cross-sectional view of another example of an infrared radiation sensor according to the invention with electrodes facing each other in a lateral direction and a centrally supported diaphragm;
• 4 shows a modification of the sensor from 3b ;
• 5 Fig. 12 shows a schematic cross-sectional view of an example of an infrared radiation sensor according to the invention, having two counter electrodes and a floating deflectable electrode;
• 6 Fig. 12 is a schematic cross-sectional view of an example of a vertical readout infrared radiation sensor not according to the present invention;
• 7 Fig. 12 is a schematic cross-sectional view of another example of a vertical readout infrared radiation sensor not according to the invention;
• 8th Fig. 12 shows a schematic cross-sectional view of an example of an infrared radiation sensor not according to the invention, having counter electrodes formed in a cover of the sensor;
• 9 shows a schematic top view of portions of the substrate of the sensor shown in FIG 8th is shown;
• 10 FIG. 12 shows a schematic three-dimensional view of sections of the sensor of FIG 8th and 9 , with portions cut off;
• 11 shows a schematic view of a membrane and supporting structures of the in 8th shown sensor;
• 12a until 12c show schematic cross-sectional views showing different operating states of the sensor of FIG 8th demonstrate;
• 13a and 13b show equivalent circuits of a sensor as shown in 8th is shown;
• 14a and 14b Fig. 12 shows a schematic view and an equivalent circuit for explaining an example of a detection circuit;
• 15a and 15b Fig. 12 shows a schematic view and an equivalent circuit for explaining another example of a detection circuit;
• 16a and 16b Fig. 12 shows a schematic view and an equivalent circuit for explaining still another example of a detection circuit;
• 17a until 17l Fig. 12 shows schematic cross-sectional views of steps of example methods for manufacturing infrared radiation sensors.

Detailed description

Hereinafter, examples of the present disclosure will be described in detail using the accompanying drawings. It should be noted that the same elements or elements having the same functionality are provided with the same or similar reference numbers, and repeated description of the elements provided with the same or similar reference numbers will typically be omitted. Thus, descriptions provided for elements with the same or similar reference numbers are interchangeable. In the following description, numerous details are set forth in order to provide a more thorough explanation of the examples of the disclosure. However, it will be appreciated by those skilled in the art that other examples may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form and not shown in detail in order to avoid obscuring the examples described herein. In addition, characteristics of the different examples described hereinafter, unless specifically noted otherwise.

Examples of the present disclosure relate to infrared radiation sensors that include a substrate. In general, the substrate may comprise one or two major surfaces, i.e. surfaces having a larger square dimension than the other surfaces thereof. The major surface of the substrate may define a substrate plane, that is, a substrate plane may pass through the major surface of the substrate even if the surface has irregularities. In general, the substrate can comprise two main surfaces and the substrate plane can be parallel to the two main surfaces of the substrate. A length direction and a width direction can be parallel to the subject plane, while a thickness direction can be vertical (or perpendicular) to the subject plane. In general, the terms “vertical” and “lateral” as used herein can mean vertical and lateral or sideways with respect to the plane of the substrate.

Examples of the present disclosure provide infrared radiation sensors that can be inexpensively manufactured using MEMS technologies. Examples create MEMS infrared radiation sensors. Examples allow for miniaturization and integration of infrared detectors into microelectronics, wherein CMOS-compatible materials and processes (CMOS=complementary metal-oxide semiconductor) can be used in fabricating the sensors. Examples of the present disclosure enable low energy infrared radiation to be received and converted into a useful signal with high efficiency.

According to examples of the present disclosure, infrared radiation is indirectly detected by measuring an electrical capacitance. In examples of the present disclosure, fewer electrical contacts are provided to the sensitive element of the sensor. In examples, the area of electrical contact may be reduced for better thermal isolation. In examples, a radiation-sensitive membrane may be placed in an evacuated cavity so that heat losses due to convective heat flux and heat removal through the atmosphere may be reduced. In examples, high thermal contrast infrared sensors can be implemented with a NETD up to 1 mK.

In examples of the present disclosure, the sensitive element is a composition comprising two layers of materials with different coefficients of thermal expansion placed one on top of the other in direct mechanical contact with each other. In examples, the sensitive element comprises a material combination of silicon and silicon oxide or silicon dioxide. The sensitive element may be carried at one position thereof and may be movable to other positions thereof. Thus, in the event of temperature changes, the sensitive element can be deflected due to the different coefficients of thermal expansion of the layer of composition. In examples, the composition is a two-material composition comprising a first layer of material having a first coefficient of thermal conductivity and a second layer of material having a second coefficient of thermal conductivity.

1a and 1b 12 show an example of an infrared radiation sensor having a membrane 10. FIG. The membrane 10 includes a semiconductor layer 12 and an oxide layer 14 formed on the silicon layer 12 . The semiconductor layer can be a silicon layer and the oxide layer can be a SiO ₂ layer. The membrane forms a sensitive element fixed to a substrate 24 on one side 10a thereof and freely movable on the other side 10b thereof. Thus, the membrane 10 forms a cantilever and the semiconductor layer 12 forms a deflectable electrode. The free end 10b has a side surface facing a side surface 16b of a stator 16 . The stator 16 has a semiconductor layer 17 forming a stationary electrode. The stator 16 may be formed in the same layer of material as the sensitive element, but is fixed to the substrate 24 and has no moveable portion. In examples, the stator does not have a movable portion because the extension of the stator in the direction of longitudinal extension of the cantilever is substantially less than the extension of the cantilever in that direction. The semiconductor materials 12, 17 of the cantilever 10 and the status 16 may be doped to be electrically conductive enough to form electrodes of a capacitor. More specifically, the free end 10b and the lateral side surface 10b of the stator 16 face each other laterally across an air gap 18, and therefore the deflectable electrode and the stationary electrode form a capacitor. A contact 20 for contacting the deflectable electrode 12 and a contact 22 for contacting the stationary electrode 16 may be provided.

1a shows the sensor element in a state in which the deflectable electrode is undeflected, indicating an equilibrium state or can be quiescent. 1b shows the sensor element under the influence of heat. 1c Fig. 12 shows an electrical equivalent circuit of the system with a variable capacitance C between the laterally facing surfaces of the semiconductor layers 12 and 17 and the electrical resistance R _m of the semiconductor layers.

Incident infrared radiation can be absorbed in the semiconductor layer 12 through interaction with free charge carriers within the doped semiconductor layer. As the charge carriers tend to assume a lower energy state, they are relaxed due to interaction with photons in the solid. Thus, the membrane is heated. Since the membrane has a combination of layers of materials with different coefficients of thermal expansion, such as Si and SiO ₂ , which are in direct contact with each other, heating the membrane leads to a deformation and therefore a reflection of the membrane, as is shown in 1b is shown schematically.

For example, silicon has a thermal expansion coefficient of about 26×10 ^-7 K ^-1 and SiO ₂ has a thermal expansion coefficient of about 5×10 ^-7 K ^-1 . Thus, the coefficient of silicon is about five times higher than that of SiO ² .

Connecting a voltage source to contacts 20 and 22 results in the in 1c shown equivalent circuit. Since thermal expansion is a reversible process, the deflection of the sensitive element 10 will vary with changing radiation intensity. Therefore, the capacitance varies between the cantilever 10 and the stator 10, and the capacitance can be read electrically. More specifically, the capacitance may change as the overlapping area of the deflectable electrode and the stationary electrode changes when viewed in the lateral direction. At the in 1a until 1c example shown, the overlapping area is in the state of 1a at a maximum.

In examples, the membrane may be pre-deflected such that the capacitance between the deflectable electrode (i.e., the sensitive element) and the stator is not at a maximum in the steady state. Thus, a readout can take place in a more linear region of capacitance variation. Pre-deflection can be achieved by depositing an oxide layer of the membrane onto the semiconductor layer at elevated temperatures such that mechanical stress develops between the layers as they cool to room temperature. Pre-deflection of the membrane may be provided with respect to all examples of the present disclosure.

Semiconductor layer 12 represents an absorption region of the membrane and may be doped with phosphorus or boron to allow absorption of infrared radiation. In order to increase the interaction of the incident photons with free charge carriers within the semiconductor, a high concentration of the dopants is desirable.

Show accordingly 1a until 1c an example of an infrared radiation sensor in which a membrane is formed in or on a substrate 24 . The semiconductor layer 12 of the membrane 10 forms a deflectable electrode and the semiconductor layer 17 of the stator 16 forms a counter-electrode. The semiconductor layer or region 17 of the stator 16 is electrically isolated from the semiconductor layer 12 . The semiconductor layer 12 and the semiconductor layer 17 face each other laterally with respect to the substrate plane, forming a capacitance C between them and therefore between the deflectable electrode 12 and the counter-electrode 16 . The membrane has a composition that has the semiconductor layer 12 and the oxide layer 14 in direct mechanical contact with each other. The semiconductor layer 12 of the cantilever beam 10 presents an absorption region configured to cause deformation of the composition by absorbing infrared radiation, which deformation results in deflection of the deflectable electrode 12 relative to the counter electrode 17, resulting in a change in the capacitance C causes.

According to the example, the capacitance or capacitor is formed by electrodes facing each other laterally. Thus, vertical spacing between the deflectable electrode and a bottom of a cavity over which the deflectable electrode may be formed is not critical to capacitance. Thus, the height of the void in the thickness direction of the substrate can be increased, and therefore the risk of necking-in can be reduced.

wobei k = 2n-1, wobei d die Dicke der Schicht ist, n eine natürliche Zahl ≥ 1 ist und λ₀ die Wellenlänge der einfallenden Infrarotstrahlung ist.In general, the layer of the composition through which the infrared radiation is incident in the absorption region can act as an antireflection layer in addition to the purpose of allowing deformation upon heating. For example, the oxide layer 14 can also serve as an anti-reflection layer and for this purpose the thickness of the anti-reflection layer can be adjusted to meet the anti-reflection condition: $$\mathrm{i.e}=k\frac{{\lambda }_0}{2}$$

where k = 2n-1, where d is the thickness of the layer, n is a natural number ≥ 1 and λ ₀ is the wavelength of the incident infrared radiation.

According to the 1a until 1c In the example shown, the membrane and therefore the flexible electrode 10 is in the form of a cantilever beam fixed at one end 10a thereof. A side face of the cantilever, such as side face 10b, may laterally face a side face of a stationary electrode, such as side face 16b. In examples, multiple side surfaces of the flexible electrode may laterally face side surfaces of one or more stationary electrodes. For example, the stator 16 can be provided to substantially surround the membrane 10 so that the front and back of the flexible electrode, which is in 1a until 1b are shown also face side faces of the stator 16 which act as stationary electrodes. Thus, a change in capacitance in the event of deflection can be increased.

In examples, a counter electrode faces the deflectable electrode laterally at a plurality of lateral edges of the deflectable electrode, and a membrane support is coupled to the membrane in a region spaced from the lateral edges of the membrane when viewed in a plan view of the substrate plane. In examples, the membrane support may be coupled to the membrane in a region spaced from any lateral edges of the membrane when viewed in a plan view of the substrate. In examples, the membrane support may be coupled to the membrane in a middle region of the membrane in a plan view of the substrate plane.

2a Fig. 1 shows an example of an infrared radiation sensor having a diaphragm supported at a central portion thereof. The sensor has a membrane 110 . The membrane 110 has a doped semiconductor layer 112 and an oxide layer 114 in direct mechanical contact with the doped semiconductor layer 112 . The doped semiconductor layer 112 and the oxide layer 114 provide a composition comprising two layers of materials having different coefficients of thermal expansion as discussed above. The sensor also includes a stationary electrode 116 forming a stator. The diaphragm 110 and the stator 116 are separated from each other by a narrow trench 118 . In examples, the width of the trench and therefore the distance between opposing lateral surfaces of the membrane 110 and the stationary electrode 116 is at most 500 nm. Thus, a capacitor structure is formed between opposing lateral surfaces of the doped semiconductor region and the diaphragm 110 and the stationary electrode 116. like it in 2 B As shown, stationary electrode 116 and membrane 112 may be formed in the same semiconductor layer.

The membrane 110 and stationary electrode 116 are electrically decoupled from a substrate in which they are formed. More specifically, the stator 116 and the diaphragm 110 are formed over a cavity 122 . A trench 124 laterally surrounds the stator 116 to electrically decouple the stator 116 from the substrate 120 . The diaphragm 110 and the stator 116 are attached to a cover 126 . The lid 126 is in 2a not shown so as not to cover the underlying structures. Also shows 2a only the structures within the outer edge of the stator 116. The cavity 122 may have a depth of about 1 micron. A further cavity 128 can be formed in the cover 126 above the membrane 110 . The membrane 110 is fixed to the cover 126 via a membrane carrier. The membrane support is formed by an oxide cylinder 130 which extends between the cover 126 in the oxide layer 114 . A contact 132 for contacting the doped semiconductor layer 112 of the membrane 110 extends through the oxide cylinder 130. Another contact 134 for contacting the doped semiconductor region of the stationary electrode 116 extends through the lid 126 and the oxide layer 114. As shown in FIG 2a As shown, contact 134 may be divided into a plurality of contacts.

At the in 2a and 2 B In the example shown, the membrane 110 is supported and electrically contacted in a central portion thereof, ie a portion separated from all lateral edges of the membrane. In examples, the portion where the membrane is supported may be the geometric center of the membrane in a plan view of the substrate plane.

In the example shown, pylons 136 are provided to stabilize the lid 126 . The pylons 136 extend through openings 138 formed in the diaphragm 110 and the stator 116. FIG. The pylons 136 may be formed from oxide pillars that mechanically connect the lid 126 to the bottom of the cavity 122 . The pylons 136 are electrically and mechanically decoupled from the diaphragm 110 and the stator 116 by trenches surrounding the pylons due to the larger dimensions of the openings 138 compared to the pylons 136.

In order to increase the active area of the capacitor between the stator 116 and the membrane 110, the trench between them in be meandering when viewed from above. In examples, the trench can be easily formed in a meander shape by etching. The lid 126 can seal the sensitive structure of the sensor with respect to the outside atmosphere. Thus, the pressure in cavities 122 and 128 can be adjusted by oxide deposition processes. In order to achieve better thermal insulation, a low pressure can be set inside the cavities in examples. In examples, the cavities may be evacuated. In general, the lid 126 and the oxide layer 114 can be transparent to infrared radiation.

The portions of the membrane 110 spaced from the fixed portion thereof constitute a deflectable electrode. The doped semiconductor layer 112 constitutes an absorption region.

As explained above, the incident infrared radiation causes the temperature of the composition of the membrane (doped semiconductor layer 112 and oxide layer 114) to rise, leading to a deformation of the composition, which deformation leads to deflection of the deflectable electrode. More specifically, the edges of the membrane 110 will flex upwards in the event of a temperature increase and therefore the capacitance between the deflectable electrode and the stator electrode 116 changes. This change in capacitance can be detected as a measure of the incident infrared radiation.

Because the only mechanical contact to the membrane 110 is via the membrane support 130 and contact 132, heat dissipation from the membrane 110 can be low. Thus, the sensitivity of the sensor can be increased.

In examples, additional trenches may be provided in the membrane to reduce thermal impact of the region coupled to the membrane support on other regions of the membrane. Such an example is in 3a and 3b shown. like it in 3a 1, trenches 150 are provided in the region where the membrane is supported by membrane support 130. FIG. like it in 3a As shown, trenches 150 are provided to form lands or latches 152 by which the portion of the diaphragm coupled to diaphragm support 130 is mechanically connected to other portions of the diaphragm. Trenches 150 may penetrate the membrane and are shown in Fig 3b Not shown. The latches 152 may include first and second latches that extend in opposite directions from the membrane support. The latches 152 may include a third latch extending from the distal end of the first latch in opposite directions perpendicular to the first latch. The latches 152 may include a fourth latch extending from the distal end of the second latch in opposite directions perpendicular to the second latch. To form such latches, the trenches 150 may include four trenches, as shown in FIG 3a is shown. In other words, the trenches 150 may be etched into the diaphragm to provide a spring structure that surrounds the diaphragm support and extends into the sides of the diaphragm. Such a spring structure can be formed by etching trenches and can serve to increase the thermal resistance of the diaphragm.

In examples, the pressure in the infrared radiation sensor, such as in the cavities surrounding the diaphragm, is kept low to reduce thermal conductivity in the cavity. Thus, heat dissipation from the sensitive structure can be reduced and sensitivity can be increased.

Operation of such a sensor was simulated using finite element analysis and showed substantial deflection of the edges of the membrane supported at a central portion thereof. Such deflection can be sensed as a change in capacitance between the deflectable electrode formed by portions of diaphragm 110 and stator electrode 116 . The change in capacitance can be detected using a suitable detector connected to terminals 132 and 134.

4 shows a schematic cross-sectional view of a modification of FIG 3b shown sensor. As in 4 As shown, an optical reflector 160 is provided on the back side of the substrate 120, that is, on the side opposite to the side on which the lid 126 is provided. In addition, an optical filter 162 is provided on the cover 126 . The optical filter 162 may be an infrared filter that blocks wavelengths other than infrared. The optical reflector 160 may be reflective to infrared radiation such that infrared radiation that passes through the absorption region and is not absorbed therein is reflected back into the absorption region. Thus, efficiency can be improved using the optical reflector. In addition, using the optical filter 162 can improve the sensitivity. Appropriate optical reflectors and filters may be provided in any of the examples described herein. Corresponding filters and reflectors can be provided in all examples of the present disclosure.

As described above, in examples of the present disclosure, at least a portion of the membrane forms a deflectable electrode and the deflectable electrode is provided with an electrical contact to enable sensing of the capacitance between the deflectable electrode and the counter electrode. In other examples of the present disclosure, the deflectable electrode is electrically floating. In the context of this disclosure, “electrically floating” means that the deflectable electrode is not provided with a galvanic connection to circuitry external to the deflectable electrode. In such examples, the infrared radiation sensor may include a first counter electrode and a second counter electrode, with a first capacitance formed between the deflectable electrode and the first counter electrode and a second capacitance formed between the deflectable electrode and the second counter electrode.

An example of an infrared radiation sensor having a floating deflectable electrode and lateral capacitances between the deflectable electrode and two counter electrodes is in US Pat 5 shown. the inside 5 The sensor shown is similar to the one in 4 sensor shown with the following exceptions. There is no galvanic electrical contact to the silicon layer 112 of the membrane 110. In this case the membrane support 130 is formed by a solid oxide cylinder. There is no contact extending through the diaphragm support 130. Instead, two separate contacts 134a and 134b are provided for two separate counter electrodes 116a and 116b. Counter electrodes 116a and 116b may be electrically isolated from each other by additional trenches formed in the semiconductor layer in which membrane 110 and counter electrodes 116a and 116b are formed. In examples, such trenches may include the counter electrode 116 shown in FIGS 2a and 3a shown, divide in half. Correspondingly, a first capacitance is formed between a lateral side surface of the deflectable electrode 110 and the counter electrode 116a, and a second capacitance is formed between another lateral side surface of the deflectable electrode 110 and the second counter electrode 116b. The first and second capacitances are connected in series through the doped silicon layer 112 . A detector may be coupled to contacts 134a and 134b to sense the capacitance of this series connection of the series capacitances and/or changes therein. Thus, incident infrared radiation can be detected by a detector connected to contacts 134a and 134b.

In examples where the deflectable electrode is electrically floating, thermal insulation of the deflectable electrode can be improved and therefore sensitivity can be increased.

In the case of the above with reference to 1 until 5 In the examples described, lateral capacitances are formed between lateral side surfaces of a deflectable electrode and one or more stationary counter-electrodes. In such examples, the area of the capacitor electrodes facing each other can be easily varied and increased by shaping the trench separating the electrodes. An example is the in 2a and 3a shown meandering ditch.

In other examples of the present disclosure, vertical capacitances are formed between surfaces of a deflectable electrode and surfaces of first and second counter electrodes that face each other in a vertical direction.

6 FIG. 12 shows a schematic cross-sectional view of an infrared radiation sensor having a membrane 210 formed in a substrate 220. FIG. In examples, membrane 210 is separated from substrate 220 by cavity 222 and trenches 224 . The membrane 210 may be supported at a central portion thereof using a membrane support 130 as described above. There is no other mechanical or electrical connection between the membrane 210 and the substrate 220. The membrane 210 has a composition of a doped semiconductor layer 112 and an oxide layer 114. FIG. Thus, incident infrared radiation causes deformation of membrane 210, portions of which form a deflectable electrode. The sensor has a first counter-electrode 226 and a second counter-electrode 228 . A first vertical capacitance is formed between portions of membrane 210 forming a deflectable electrode and first counter electrode 226 and a second vertical capacitance is formed between other portions of membrane 210 forming a deflectable electrode and second counter electrode 228 . The first and second counter electrodes 226, 228 may be electrically connected to a sensing circuit 230 as shown in FIG 6 is represented by dashed lines.

Deformation of the deflectable electrode 210 causes the first and second capacitances to change. There is again a series connection between the first capacitance and the second capacitance via the doped semiconductor layer 112. In the case of FIG 6 In the example shown, the oxide layer 114 contributes to the capacitances. In other examples, the oxide layer 114 may be on the side of the diaphragm 112 be arranged which faces away from the counter-electrodes 226, 228.

7 Figure 12 shows a schematic cross-sectional view of another example of a vertical readout infrared radiation sensor. A diaphragm 210 ′ in the form of a cantilever is formed in a substrate 220 and is separated from the substrate by a cavity 222 and a trench 224 . Again, the membrane 210' may include a doped silicon layer 112 and an oxide layer 114 and therefore has a layered composition with at least two layers of materials with different coefficients of thermal expansion. The infrared radiation sensor further includes a first counter electrode 236 and a second counter electrode 238 provided on the bottom of the cavity 222 . The first and second counter electrodes 236, 238 face respective portions of the membrane 210' in a vertical direction. The first and second counter-electrodes 236, 238 can, as is shown in 7 indicated in dashed lines may be connected to a detection circuit 230 . As explained in more detail above, infrared radiation incident on the doped semiconductor layer 112 leads to a deformation of the semiconductor layer. Such deformation results in a deflection of the diaphragm 210' and therefore a change in the first and second capacitances. Such a change can be detected by the detection circuit 230 via a change in the series capacitance formed by the first and second capacitances coupled through the doped semiconductor layer 112 .

In examples, the portion of the membrane forming the deflectable electrode is vertically deflectable with respect to the substrate plane, with deformation of the composition causing vertical deflection of the portion of the deflectable electrode relative to the first counter electrode and the second counter electrode. In examples, the deflectable electrode and the first counter-electrode face each other laterally with respect to the substrate plane, and the deflectable electrode and the second counter-electrode face each other laterally with respect to the substrate plane. In other examples, the deflectable electrode and the first counter-electrode face each other vertically with respect to the substrate plane, and the deflectable electrode and the second counter-electrode face each other vertically with respect to the substrate plane.

In the above examples, portions of the membrane form a deflectable electrode and the membrane comprises the composition. In other examples, the membrane is supported on the substrate by the composition. In such examples, the membrane may be formed from a single layer and may be coupled to the substrate via the composition having at least two layers of material with different coefficients of thermal expansion. In such examples, the composition may comprise a first cantilever beam and a second cantilever beam, the first cantilever beam and the second cantilever beam supporting the membrane, with a free end of the first cantilever beam having a first side of the membrane and a free end of the second cantilever is coupled to a second side of the membrane opposite the first side in a lateral direction with respect to the plane of the substrate. One such example is below with reference to FIG 8th until 16 described.

Like it in the 8th until 11 As shown, an infrared radiation sensor includes a substrate 220 . A cavity 222 is formed in the substrate 220 and defines a semiconductor layer of the substrate. First and second cantilever beams 302, 304 and a diaphragm 310 are patterned in this semiconductor layer by trenches 306 penetrating the semiconductor layer. Each cantilever beam 302, 304 has a composition of a doped semiconductor layer 312 with an oxide layer 314. FIG. The membrane 310 includes the doped silicon layer 312, but not the oxide layer 314 in this example.

The sensor also has a first counter-electrode 320 and a second counter-electrode 322 . The first and second counter electrodes 320,322 are formed in an infrared radiation sensor lid 326 which seals the cavity in which the diaphragm 310 and cantilever beams 302,304 are formed. Contacts 324 and 326 as shown in 10 may be provided to connect the counter electrodes 320, 322 to a sensing circuit. In the schematic perspective view of 10 the lid 326 is shown translucent so as not to obscure the structures beneath it.

9 FIG. 12 shows a schematic plan view of the semiconductor layer in which the cantilever beams 302, 304 and the membrane 310 are formed. First ends 302a and 304a of the cantilever beams may be fixed to the substrate 220 . A second end 302b of the cantilever beam 302 is mechanically connected to the diaphragm 310 via a spring structure 330 and a second end 304b of the cantilever beam 304 is mechanically connected to an opposite end of the diaphragm 310 via a spring structure 332 . The first counterelec Rode 320 faces a portion of the deflectable membrane 310 in a vertical direction and the second counter electrode 322 faces another portion of the deflectable membrane 310 in a vertical direction. Correspondingly, a first capacitance is formed between the first counter-electrode 320 and the deflectable electrode 310 and a second capacitance is formed between the second counter-electrode 322 and the deflectable electrode 310 . Again there is a series connection between the first and second capacitances through the conductively doped silicon layer 312 which forms the deflectable electrode.

One end 302a , 304a of the cantilever beams 302 may be mechanically fixed to the substrate 220 . In examples, ends 302a, 304a may be mechanically fixed via oxide bridges or oxide pylons. The other sides 302b, 304b of the bi-material cantilever beams are attached to different sides of the membrane 310. FIG. Mechanical torsion springs 330 and 332 may be provided to ensure maximum deflection of the cantilever beams by decoupling relative to rotation of the ends 302b, 304b from the membrane 310 forming a stiffer central portion. Like it from 11 As can be seen, due to the torsion springs 330, 332, the diaphragm 310 can have a flat profile which can be optimal for a readout and which can contribute to the highest possible output signal. In other words, the torsion springs 330, 332 support the metal diaphragm 310 while allowing the entire structure to relax, thus promoting a greater swing and flutter profile.

Diaphragm 310 is formed of heavily doped semiconductor, such as silicon, and is used as a movable floating contact for sensing, readout, and IR absorption. In this example, the cantilever beams 302, 304 are composed of two layers of materials with different coefficients of thermal expansion to convert temperature changes to mechanical deformations. In examples, the cantilevers may be bi-material cantilevers having a silicon layer and a deposited oxide layer. Infrared radiation incident on the membrane 310 can cause a temperature increase in the membrane 310, which in turn can cause a temperature increase in the cantilever beams 302, 304 and therefore mechanical deformation thereof. This deformation of the cantilevered beams 302, 304 results in a deflection of the membrane 310, as shown in FIG 11 is shown. This deflection results in a change in capacitance which can be detected by a sensing circuit connected to the counter electrodes 320,322. Accordingly, the cantilevered beams may be viewed as representing a bi-material pair configured to convert heat generated in the membrane into vertical displacement thereof.

The cap 326 may be a silicon oxide cap and may seal the cavity in which the deflectable electrode is placed. Thus, a vacuum cavity can be formed to ensure minimal heat loss. The cavity 222 may be formed by a Venezia cavity, which allows electrical and thermal isolation of the membrane from the substrate.

12a until 12c show the sensor of 8th until 11 in different operating states. In 12a the membrane is in the undeflected state, such as the steady state. In 12b the membrane is deflected upwards when the membrane is heated. In 12c the membrane is deflected downwards. This condition can be reached when the membrane is cooled, starting from the undeflected condition. 13a Fig. 13 shows an equivalent circuit having a variable capacitance Cn between the counter electrode 320 and the membrane 310, a variable capacitance Cr between the counter electrode 322 and the membrane 310 and a variable capacitance Cb between the membrane and the bulk of the substrate under the membrane . The contact 324 of the first counter-electrode 320, the contact 326 of the second counter-electrode 322 and a bulk contact 350 are also in 13a shown. 13b FIG. 12 shows a corresponding equivalent circuit where the membrane 310, which is formed from highly doped conductive semiconductor material, has collapsed into a circuit node.

Because the membrane 310 is floating, the overall charge within the membrane remains the same and therefore electrostatic forces are balanced at all times. Thus, the risk of pull-in effects occurring is reduced.

14a until 16b show schematic views and equivalent circuits for explaining examples of possible detection circuits. In all examples, the bulk contact is connected to ground.

According to 14a a supply voltage Vdd is applied to the contact 324 and therefore the first counter electrode 320 and an output voltage Vout at the contact 326 is sensed. The output voltage 326 depends on the deflection of the membrane 310 and therefore provides a measure for the incident infrared radiation. Correspondingly 14a and 14b can be seen as showing an unbalanced readout with no pull-in.

15a and 15b show a readout using reference pixel offset cancellation and pull-in cancellation for symmetric feed. An infrared radiation sensor 400 has a structure as referred to above 8th until 11 is described. A reference structure 402 has a similar structure. However, a shielding layer 404 is provided so that no infrared radiation impinges on the membrane of the reference structure 402 . A supply voltage Vdd is applied to a counter electrode of the sensor structure 400 and a supply voltage Vss is applied to a counter electrode of the reference structure 402 . The other counter electrodes are connected to each other and to an output contact 410 . The output voltage Vout is sensed at the output pin 410 . like it in 15b is shown, the capacitances of the sensor structure 400 are variable depending on the infrared radiation and the capacitances of the reference structure do not change due to the shielding layer 404.

16a and 16b show direct sensor and reference integration in an inverting amplifier with capacitive feedback. The supply voltage Vdd is applied to the first counter electrode 320 via the contact 324 . The voltage at the second counter-electrode is applied to a first input of a differential amplifier 420 . A reference voltage is applied to a second input of differential amplifier 420 . The output voltage Vout of amplifier 420 is a measure of the infrared radiation impinging on the sensor. The output of the differential amplifier is connected to the first input of the differential amplifier 420 via a feedback capacitor Cf. The output of the differential amplifier depends on the relationship between the feedback capacitor Cf and the capacitance at the first input of the differential amplifier 420 and is therefore a measure of the incident infrared radiation.

Even though 14a until 16b in connection with an infrared radiation sensor as described in US Pat 8th until 11 is shown, it is clear that a corresponding reading can also take place with the other examples of infrared radiation sensors described herein. In addition, any other circuit arrangement for detecting the respective capacitance or changes in the respective capacitance can be used.

In examples of the present disclosure, thermal isolation of the deflectable electrode may be improved since thermally insulating materials may be used to mechanically contact the sensing membrane. In examples, mechanical springs may promote maximum displacement of cantilever beams and maximum possible mean displacement of a conductive membrane. In examples, using an electrically isolated and "floating" structure can eliminate the pull-in effect since the top and bottom electrostatic forces can always balance. Spring systems as described in connection with examples of the present disclosure can work most efficiently when all electrostatic effects are compensated, so that there is a reduced risk of being pulled in.

In examples, the sensor structure may be integrated into a substrate or chip along with readout circuitry as described herein. Examples of the present disclosure relate to infrared radiation sensors, which may be implemented in MEMS technology using CMOS-compatible materials and processes.

Examples relate to methods of making an infrared radiation sensor in which a layer disposed over a cavity in a substrate is formed, the layer including an absorber layer. A deflectable electrode or a deflectable electrode and a supporting structure for the deflectable electrode are produced by patterning the layer. A composition comprising at least two layers of materials with different coefficients of thermal expansion is created before or after patterning the layer on the deflectable electrode or support structure. A first counter-electrode facing the deflectable electrode is created such that a first capacitance is formed between the first counter-electrode and the deflectable electrode. A second counter-electrode facing the deflectable electrode is created so that a second capacitance is formed between the second counter-electrode and the deflectable electrode. The deflectable electrode is floating, i.e. there is no galvanic connection to the deflectable electrode.

Examples provide a method of making an infrared radiation sensor that includes creating a layer disposed over a cavity in a substrate. A deflectable electrode is created by patterning the layer, wherein at least one lateral surface of the layer surrounding the deflectable electrode has a Counter electrode forms, which faces a lateral surface of the deflectable electrode. A lateral capacitance is formed between the lateral faces that face each other laterally. A composition comprising at least two layers of materials with different coefficients of thermal expansion is created before or after patterning the layer on the deflectable electrode.

Examples of methods for manufacturing infrared radiation sensors as described in 3b and 5 are shown below with reference to FIG 17a until 17l described. It goes without saying that corresponding steps can also be carried out when manufacturing infrared radiation sensors according to other examples described herein.

like it in 17a As shown, a semiconductor substrate 500 having a cavity 502 is prepared such that a semiconductor layer 504 is disposed over cavity 502 . At least the semiconductor layer 504 can be highly doped. The cavity 502 can be formed by a so-called Venezia process. The Venezia process may include etching trenches in a surface of the semiconductor substrate, annealing the semiconductor substrate in an H atmosphere to cause the semiconductor material to flow back so that the bottoms of the trenches are connected and the top portions of the trenches are closed, to form a buried cavity under the surface of the semiconductor substrate. In other examples, cavity 502 may be formed using a sacrificial layer process. The substrate 500 can be a silicon substrate.

like it in 17b As shown, an oxide layer 506 is formed on the substrate 500 to cover the semiconductor layer 504 . The oxide layer 500 can be deposited using chemical vapor deposition at elevated temperatures of 400 to 500°C so that pre-deflection of a membrane to be produced can take place after cooling to room temperature. A first deep trench etch then takes place to create a first deep trench 508 . A sacrificial layer 510 is then applied and structured, see FIG 17c . The sacrificial layer is later removed to form the lower cavity over the deflectable electrode. In examples, the sacrificial layer may be a carbon layer. Another oxide layer 512 is then deposited, such as by chemical vapor deposition. Planarization may take place to remove surface asperities of the oxide layer 512 . For example, chemical mechanical polishing can be performed to reduce or remove surface asperities. A second deep trench etch then takes place, as shown in 17d is shown. Thus, further deep trenches 514 are formed in order to pattern the semiconductor layer 504 in order to reach the membrane structures 520 and the counter-electrode structures 522 in the semiconductor layer. In the second deep trench etch, the semiconductor layer 504 can be patterned to form a single counter electrode 116 (as described in 3b is shown) or to obtain separate counter electrodes 116a, 116b, as is shown in 5 is shown.

17e until 5 p.m relate to a process for manufacturing an infrared radiation sensor as described in 3b is shown, in which the membrane 110 has an external contact. For this purpose, through-holes are etched, which reach to the counter-electrode 116 and the membrane 110. FIG. The through holes can be filled with conductive material such as tungsten. Metallization can then take place to form a contact 134 for the counter electrode 116 and a contact 132 which contacts the membrane 110 . Even though 17e until 5 p.m show a symmetrical structure with two counter-electrode contacts 134, 134`, a single contact may be sufficient. An additional oxide layer 524 may be formed on oxide layer 512 during this process.

Thereafter, openings 530 reaching the sacrificial layer 510 are formed through the oxide layers 512 and 524, as shown in FIG 17f is shown. The sacrificial layer 510 is removed through the openings 530 to create the cavity 128 over the membrane. An additional layer of oxide 532 is then deposited to seal cavities 128 and 502 . Finally, an optical filter 562 can be applied to the oxide layer 532 and an optical reflector 560 can be applied to the backside of the substrate 500. FIG.

Contacts 132, 134 can be coupled to external circuitry.

17i until 17l show part of a process used to manufacture an infrared radiation sensor as shown in 5 is shown, is suitable, which corresponds to that in 17a until 17d shown process follows. the inside 17i until 17l The process shown differs from that in 17e until 5 p.m shown process in that no contact to the membrane 110 is formed. Instead, two separate contacts 134a and 134b are formed to both counter electrodes 116a and 116b. Otherwise the process is similar to that referred to 17e until 5 p.m described process.

In examples, the composition is a layered composition having at least two layers of materials with different coefficients of thermal expansion that are in direct mechanical contact with each other. In examples, a layer may be formed from a doped semiconductor layer, such as silicon or germanium. In examples, the other layer may be formed by an oxide layer such as silicon oxide, silicon dioxide, or germanium oxide. In examples, the first layer is doped silicon and the second layer is silicon dioxide, with the coefficient of thermal expansion of silicon being almost five times higher than that of silicon oxide or silicon dioxide. Thus, in the event of a temperature rise, substantial deflection can be achieved.

Examples provide an infrared camera having an array of infrared radiation sensors as disclosed herein. In general, the size of the membrane affects the sensitivity of the sensor element since the larger the size of the membrane, the greater the change in the active area of the capacitor due to mechanical deformation of the membrane. Correspondingly, examples can relate to sensors with a high sensitivity. Such sensors can be useful as sensor elements in CO ₂ sensors where a sensitivity of 1 mK is desirable. In other applications, the sensor elements can be scaled down to a reduced size to implement small, high resolution infrared cameras.

In examples, the composition has two layers of materials with different coefficients of thermal expansion. In other examples, the composition may have more than two layers of materials with different coefficients of thermal expansion, such examples may have increased sensitivity.

In examples described herein, an oxide layer of the composition can act as a filter stack deposition on the semiconductor layer. In examples, bi-material parts are only in the cantilever and do not contribute to the optical performance. In such examples, a filter stack may be applied to the lid. In examples, an oxide layer may be deposited over the entire semiconductor membrane and may be used as an anti-reflective coating. In examples where oxide is applied only to the cantilevers and the surface of the membrane is not covered with a layer of oxide, optical components may be included in the lid. In examples, a Venezia process can be used to create the semiconductor layer in which the membrane is formed. The Venezia process can allow membranes to be formed with little or no charge. Otherwise, additional charges trapped in deposited layers can be a source of imbalance. Accordingly, using the Venezia process can help create a symmetrical system and can help reduce mechanical stress so that overall mechanical performance can be improved.

In examples, the deflectable electrode is vertically deflectable with respect to the substrate plane. In such examples, a membrane plane defined by major surfaces of the membrane in an undeflected state may be arranged parallel to the substrate plane. In other examples, the deflectable electrode may be laterally deflectable with respect to the substrate plane. In such examples, a membrane plane defined by major surfaces of the membrane may be vertical to the substrate plane.

Claims (4)

An infrared radiation sensor, comprising: a substrate (24, 120) having a major surface defining a substrate plane; a membrane (10, 110) formed in or on the substrate (24, 120), at least a portion of the membrane (10, 110) forming a deflectable electrode; and a counter electrode (116, 116a, 116b); wherein the deflectable electrode and the counter-electrode (116, 116a, 116b) face each other laterally with respect to the substrate plane, wherein a capacitance is formed between the deflectable electrode and the counter-electrode (116, 116a, 116b), wherein the membrane (10, 110) comprises a composition comprising at least two layers (12, 14, 112, 114) of materials having different coefficients of thermal expansion and wherein the composition comprises an absorption region configured to cause deformation of the composition by absorbing infrared radiation, wherein the deformation leads to a vertical deflection of the deflectable electrode relative to the counter-electrode (116, 116a, 116b) with respect to the substrate plane, which causes a change in the capacitance, the counter-electrode (116, 116a, 116b) of the deflectable electrode on a plurality of lateral Edges of the deflectable electrode facing, wherein a membrane support (130) with the Mem membrane (110) is coupled in a region spaced from lateral edges of the membrane (110), seen in a plan view of the substrate plane, and wherein the membrane support (130) is coupled to the membrane (110) in a central region of the membrane (110), in a plan view of the substrate plane. An infrared radiation sensor that has the following characteristics: a substrate (24, 120) having a major surface defining a substrate plane; a membrane (10, 110) formed in or on the substrate (24, 120), at least a portion of the membrane (10, 110) forming a deflectable electrode; and a counter electrode (116, 116a, 116b); wherein the deflectable electrode and the counter-electrode (116, 116a, 116b) face each other laterally with respect to the substrate plane, wherein a capacitance is formed between the deflectable electrode and the counter-electrode (116, 116a, 116b), the membrane (10, 110) having a composition comprising at least two layers (12, 14, 112, 114) of materials having different coefficients of thermal expansion, and wherein the composition has an absorption region configured to cause deformation of the composition by absorbing infrared radiation, the deformation resulting in vertical deflection, with respect to the substrate plane, of the deflectable electrode relative to the counter electrode (116, 116a, 116b). , which causes a change in capacitance, the counter electrode (116, 116a, 116b) facing the deflectable electrode at a plurality of lateral edges of the deflectable electrode, a membrane support (130) being coupled to the membrane (110) in a region separated from lateral edges of the membrane (110) is spaced, seen in a plan view of the substrate plane, wherein the membrane (110) has trenches (150) that reduce a thermal influence of the region coupled to the membrane support (130) on other regions of the membrane (110). The infrared radiation sensor according to any one of Claims 1 and 2 , in which the edges of the deflectable electrode and sections of the counter-electrode (116, 116a, 116b), which face one another, are meander-shaped in a plan view of the substrate plane. The infrared radiation sensor according to any one of Claims 1 until 3 , in which a first layer (12, 112) of the membrane (10, 110) is formed in a doped semiconductor layer of the substrate (24, 120), the counter-electrode (116, 116a, 116b) being formed in the doped semiconductor layer and of of the membrane (10, 110) is separated by trenches (18, 118).

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