Thermal detector for electromagnetic radiation comprising a transducer, diode thermometers

Abstract

The invention relates to a thermal detector comprising: a readout substrate (10), including a readout circuit (12); and an absorbing membrane (30), suspended above and thermally insulated from the readout substrate (10), and including a thermometer transducer electrically connected to the readout circuit (12). The thermometer transducer is formed of several thermometer diodes (D1, D2) connected in parallel, and the readout circuit (12) is adapted to selectively activate the thermometer diodes (D1, D2). The thermometer diodes (D1, D2) and the readout circuit (12) are configured to exhibit at least two of the following electrical configurations: a configuration where the total electric current Id flowing through the thermometer transducer has a first value of Id,1; and another configuration where the total electric current Id has a second value of Id,2 different from Id,1. Figure for the abstract: Fig. 1B

Description

Title of the invention: Thermal detector of electromagnetic radiation comprising a diode thermometer transducer technical field

[0001] The field of the invention is that of thermal detectors of electromagnetic radiation, for example terahertz or infrared, comprising a membrane suspended above a reading substrate where a thermometer transducer formed of at least one diode is located. PREVIOUS STATE OF THE ART

[0002] Thermal detectors of electromagnetic radiation, for example terahertz or infrared, may comprise an absorbing membrane suspended above a reading substrate and thermally insulated from it. The absorbing membrane includes an absorber of the electromagnetic radiation to be detected, and a thermometer transducer, thermally connected to it, whose electrical property varies according to its heating. Such a thermometer transducer may be a thermistor (for example, vanadium or titanium oxide, or even amorphous silicon), a diode (pn or pin junction), or even a metal-oxide-semiconductor field-effect transistor (MOSFET).

[0003] A thermometer diode has the advantage of exhibiting a low thermal resolution ATmin compared to other types of thermometer transducers, which gives the thermal detector high sensitivity in terms of minimum detectable power (MDP). However, the thermal resolution ATmin of the thermometer diode depends in particular on its bias point in Id(Vd). Furthermore, the electric current Id flowing through the thermometer diode leads to heat dissipation by Joule heating, which generates self-heating of the absorbing membrane. This self-heating improves the sensitivity of the thermal detector, but degrades its speed in terms of effective thermal response time 1*^. Therefore, it appears that it is not possible to optimize one of these performance parameters (sensitivity and speed) without degrading the other.

[0004] Furthermore, during the manufacture of a thermal detector, the thermometer diode is usually sized to obtain a low thermal resolution ATmin, with a compromise made to achieve sufficient sensitivity and speed (or by prioritizing either sensitivity or speed). During the operation of the thermal detector, it is not possible to adjust its performance in terms of sensitivity and speed to meet the desired requirements, except by modifying the bias voltage Vd of the thermometer diode, but this then leads to a degradation of its thermal resolution ATmin, and therefore of the sensitivity of the thermal detector. Description of the invention

[0005] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to offer a thermal detector of electromagnetic radiation, for example terahertz or infrared radiation, which has improved performance, in particular which allows the performance to be adjusted in a controlled manner, in order to favor the sensitivity or the speed of the thermal detector, without degrading the thermal resolution of the thermometer transducer.

[0006] To this end, the object of the invention is a thermal detector of electromagnetic radiation, comprising: a reading substrate, including a reading circuit; and an absorbing membrane, suspended above the reading substrate and thermally insulated from it, and including a thermometer transducer electrically connected to the reading circuit and biased by the latter with a voltage Vd

[0007] According to the invention: the thermometer transducer is formed of several thermometer diodes connected in parallel; the reading circuit is adapted to activate the thermometer diodes selectively; and the thermometer diodes and the reading circuit are configured so as to present at least the following two electrical configurations: a first configuration where a total electric current Id flowing in the thermometer transducer biased at the voltage Vd has a first value Id4; and a second configuration where the total electric current Id has a second value Id>2 different from Id4.

[0008] Some preferred but not limiting aspects of this thermal detector are the following.

[0009] The thermometer diodes can be lateral diodes each comprising two doped lateral regions and a central region located, in a plane parallel to the main plane of the absorbing membrane, between the two doped lateral regions.

[0010] The thermometer diodes can be made of the same crystalline semiconductor material.

[0011] The thermometer diodes can be mounted symmetrically, and can each have an identical or different width from one thermometer diode to another.

[0012] The thermometer diodes can be mounted in an antisymmetrical manner, and can each have a different width from one thermometer diode to another.

[0013] The absorbing membrane can be held suspended by thermal insulation arms extending to anchoring pillars, and polarization conductive tracks can extend from the anchoring pillars through the thermal insulation arms to come into electrical contact with the thermometer diodes.

[0014] The same polarization conductive track can be in electrical contact with an anode or a cathode of at least two thermometer diodes connected in a symmetrical arrangement.

[0015] The same polarization conductive track can be in electrical contact with an anode and a cathode of at least two thermometer diodes connected in an antisymmetric arrangement.

[0016] The reading circuit may include at least one switch or at least one two-way switch connected to the thermometer diodes to activate the thermometer diodes selectively.

[0017] The thermal detector is preferably adapted to detect terahertz radiation or infrared radiation. Brief description of the drawings

[0018] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0019] [Fig.1A] is a schematic and partial cross-sectional view of a thermal detector according to one embodiment, here in the case of a thermal detector of terahertz radiation;

[0020] [Fig.1B] is a schematic and partial top view of the thermal detector illustrated in [Fig.1A];

[0021] [Fig.1C] illustrates the equivalent electrical circuit of the thermometer diodes and the thermal detector reading circuit illustrated in [Fig.1B];

[0022] [Fig.2A] is a schematic and partial top view of a thermal detector according to an alternative embodiment;

[0023] [Fig.2B] illustrates the equivalent electrical circuit of the thermometer diodes and the thermal detector reading circuit illustrated in [Fig.2A];

[0024] [Fig.3A] is a schematic and partial top view of a thermal detector according to another embodiment;

[0025] [Fig.3B] illustrates the equivalent electrical circuit of the thermometer diodes and the thermal detector reading circuit illustrated in [Fig.3A];

[0026] [Fig.4A] is a schematic and partial top view of a thermal detector according to another embodiment;

[0027] [Fig.4B] illustrates an example of the evolution of the self-heating gain gÆ as a function of the total width of the polarized thermometer diodes, in the case of the thermal detector of [Fig.4A].

[0028] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0029] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are inclusive, unless otherwise stated.

[0030] Figures IA and IB are schematic and partial views of a thermal detector 1 according to one embodiment, in cross-section ([Fig. 1A]) and in top view ([Fig. 1B]). [Fig. 1C] illustrates an equivalent electrical circuit of the thermometer diodes D1, D2 and the reading circuit 12.

[0031] In general, the thermal detector 1 according to the invention is adapted to absorb electromagnetic radiation, for example in the terahertz or infrared range. The thermal detector 1 can thus be particularly adapted to detect terahertz radiation whose central wavelength Xc is within a predefined spectral range from approximately 0.1 mm to 1 mm (spectral range between approximately 0.3 and 3 THz), or even to detect infrared radiation, for example, from the LWIR (Long Wavelength Infrared) range whose wavelength is between approximately 8 pm and 14 pm.

[0032] In this example, the thermal detector 1 is adapted to detect terahertz radiation. It can belong to an array of identical thermal detectors arranged mutually at a spacing of, for example, 50 pm. Only one of the detection pixels of the thermal detector array is shown here. Furthermore, the thermal detector 1 includes an absorbing membrane 30 suspended above and thermally insulated from a reading substrate 10. The absorbing membrane 30 includes a thermometer transducer formed of several thermometer diodes connected in parallel by the reading circuit, here diodes D1 and D2. The configuration of the absorbing membrane 30 and the thermometer diodes D1 and D2 is described here for illustrative purposes; as explained later, other configurations are possible.

[0033] Here and for the remainder of the description, a three-dimensional direct frame XYZ is defined, where the XY plane is substantially parallel to the plane of the reading substrate 10, the Z axis being oriented in a direction substantially orthogonal to the plane of the reading substrate 10 in the direction of the absorbing membrane 30. The terms "lower" and "upper" are understood to be relative to an increasing positioning when moving away from the reading substrate 10 in the +Z direction.

[0034] The thermal detector 1 comprises a functionalized substrate 10, called the readout substrate, made in this example of silicon, comprising a readout circuit 12 for controlling and reading the thermal detectors. The readout circuit 12 is here in the form of a CMOS integrated circuit located in a support substrate 11. It comprises portions of conductive lines (not shown), for example metallic, separated from each other by an electrically insulating material, for example a silicon-based mineral material such as silicon dioxide (SiOx), silicon nitride (SiNx), or their alloys. It may also include active electronic elements (not shown), for example diodes, transistors, or passive electronic elements, for example capacitors, resistors...connected by electrical interconnections to the absorbing membrane 30 on one side, and to a connection pad (not shown) on the other, the latter being intended to connect the thermal detector 1 to an external electronic device.

[0035] As detailed below, the reading circuit 12 is adapted to voltage-bias the thermometer transducer to a predefined value Vd, which can be chosen to optimize the thermal resolution ATmin. Furthermore, since the thermometer transducer is composed of several thermometer diodes connected in parallel (here, diodes DI and D2), the reading circuit 12 is adapted to activate the thermometer diodes (i.e., to bias them in the forward direction) independently of each other, i.e., selectively. To achieve this, the reading circuit includes one or more switches. Thus, a diode that is not activated is either unbiased or biased in the reverse direction: in both cases, it carries little or no electric current.

[0036] The thermal detector 1 preferably comprises a reflector 20, made of at least one material reflective to the terahertz radiation to be detected. It rests here on the surface of an insulating layer of the readout substrate 10. Alternatively, it can be formed from a portion of the conductive line of the last electrical interconnection level of the CMOS integrated circuit, and thus be located within the readout substrate 10.

[0037] The reading substrate 10 and the reflector 20 are here covered by an insulating layer 21 made of a dielectric material, such as silicon oxide. This insulating layer 21 allows, in particular, the height of a cavity formed between the reflector 20 and a high-impedance surface 23 to be adjusted. Its thickness can be adjusted to optimize the absorption of the radiation to be detected by an absorber 36 located on the absorbing membrane 30. It can thus be substantially equal to X / 4n where / is a reference wavelength of terahertz radiation to be detected and where n is the refractive index of the insulating layer 21.

[0038] The thermal detector 1 here includes connecting pillars 22, made of an electrically conductive material, which pass through the insulating layer 21 and ensure the electrical connection between anchoring pillars 24 and the reading circuit 12.

[0039] The thermal detector 1 here comprises a high-impedance surface (HIS) 23, adapted to reflect the terahertz radiation to be detected without phase shift. It is located below the absorbing membrane 30 and at a distance from it along the Z-axis, and is coupled to an absorber 36 located on the absorbing membrane 30, here a resistive dipole. In this example, the high-impedance surface 23 rests on the reading substrate 10, and here on the insulating layer 21. It is spaced from the reflector 20 and the absorber 36 by a distance that optimizes the absorption of the terahertz radiation by the absorber 36. The high-impedance surface 23 is made of a material chosen from aluminum, copper, gold, among others, and has a thickness, for example, between 50 nm and 500 nm, preferably on the order of 300 nm.

[0040] The thermal detector 1 comprises a thermometric membrane 30, suspended above the reading substrate 10 and here above the high-impedance surface 23 by anchoring pillars 24, and insulated from it by thermal insulation arms 25. The anchoring pillars 24 and the thermal insulation arms 25 also provide the electrical connection of the thermometer transducer to the reading circuit 12 (here via the connecting pillars 22). The anchoring pillars 24 are made of at least one electrically conductive material and are electrically connected to the underlying connecting pillars 22 (and here extend vertically from them). The thermal insulation arms 25 include a layer 33 made of at least one electrically conductive material, which extends from the anchoring pillars 24 to the diodes Dl, D2, forming conductive biasing tracks to allow the thermometer diodes Dl, D2 to be voltage biased to a predefined value Vd.

[0041] The absorbing membrane 30 therefore includes a thermometric transducer, formed here of several diodes D1, D2, etc., called thermometer diodes. The thermometer diodes D1, D2 rest on an insulating lower layer 31, made for example of amorphous silicon or another electrically insulating material, and are in contact with bias pads 35, which are in electrical contact with the conducting bias tracks 33.

[0042] The thermometer transducer comprises at least two thermometer diodes. In this example, two thermometer diodes D1, D2 are shown, but more diodes may be present, for example three or four diodes, depending in particular on the configuration of the bias conductive tracks 33.

[0043] The thermometer diodes D1, D2 are lateral diodes, in the sense that the injection of charge carriers into the semiconductor junction is horizontal (approximately parallel to the XY plane) and not vertical (along the Z-axis). They are formed of a layer of crystalline semiconductor material, for example silicon, consisting of two doped lateral regions of type p (anode D1.1 for diode D1) and type n (cathode D1.3), between which lies a central region (D1.2) that is unintentionally undoped or lightly doped. The lateral and central regions are aligned in the XY plane along a longitudinal axis (here parallel to the X-axis). The two lateral regions are preferably overdoped to ensure good ohmic contact with biasing pads.

[0044] The semiconductor layer of each thermometer diode D(i) has a length L, a width W(i), and a thickness e. Preferably, the length L is identical for all thermometer diodes. Preferably also, the thickness e is identical for all thermometer diodes. Preferably, the level and type of doping of the lateral and central regions are identical for all thermometer diodes. Finally, the width W of the thermometer diodes may or may not be identical, depending on the type of electrical assembly. Preferably, the width of a thermometer diode is constant along its longitudinal axis. The width of a thermometer diode is defined as the dimension of the semiconductor layer in the XY plane and along an axis orthogonal to the longitudinal axis. In the case of a symmetrical electrical assembly such as those in [Fig. 1C] and [Fig. 2B], the width of the thermometer diodes may be identical or different from one diode to another.Conversely, in the case of an antisymmetric electrical configuration such as that of [Fig. 3B] (also called a back-to-back configuration), the width W® of the temperature diodes differs from one diode to another. Note that in a symmetrical configuration, the temperature diodes are oriented in the same way with respect to the applied voltage, whereas in an antisymmetric or back-to-back configuration, the diodes have opposite orientations with respect to the applied voltage.

[0045] The temperature diodes D1, D2 are connected in parallel to each other to the reading circuit 12, which is adapted to bias them by applying a predefined value Vd. Furthermore, the reading circuit 12 is adapted to activate the temperature diodes D1, D2 (i.e., to bias them in the forward direction) independently of each other. For this purpose, the reading circuit 12 includes at least one switch, here two switches. In this example, the reading circuit 12 can bias, by actuation of the switches, one or the other of the temperature diodes, or all of the temperature diodes simultaneously.

[0046] The thermometer diodes D1, D2 are covered with an insulating intermediate layer 32. The bias conductive tracks 33 extend over this insulating intermediate layer 32 and make contact with the bias contacts 35. In this example, two conductive tracks 33 are in electrical contact with the anode D1 and the cathode D1 of the thermometer diode D1, and two other conductive tracks 33 are in electrical contact with the anode and cathode of the thermometer diode D2. Here, each of the four thermal insulation arms 25 is traversed by a bias conductive track 33.

[0047] An insulating top layer 34 covers the conductive tracks 33 and the biasing pads 35. The absorber 36 is formed by an antenna with a resistive load matched to its impedance (resistive dipole) which rests here on the insulating top layer 34, and may be coated with a protective layer (not shown). The absorber 36 is adapted to dissipate heat by Joule heating when an electric current flows through it. It is arranged in the absorbing membrane 30 so as to be in thermal contact with the temperature diodes D1, D2 (thermal coupling), so that the heat dissipated by Joule heating leads to an increase in the temperature of the temperature diodes D1, D2. It is here spaced and electrically isolated from the thermometer diodes D1, D2 by the upper insulating layer 34, which can be made for example of a silicon oxide or nitride and can have a thickness for example of the order of approximately 1000m.However, other arrangements of the resistive load with respect to the temperature diodes are possible. It can, for example, be located below the temperature diodes.

[0048] In general, the thermometer diodes D1, D2 and the reading circuit 12 are configured so as to present at least the following two electrical configurations: a first configuration where the total electric current Id flowing in the thermometer transducer (i.e. in the thermometer diodes biased in the forward direction) has a first value Id.i; and a second configuration where the total electric current Id has a second value Id>2 different from Id>i.

[0049] In this example, the thermometer diodes D1, D2 are mounted symmetrically, and the readout circuit 12 can selectively bias one or both of the thermometer diodes D1, D2. The thermometer diode D1 has a width Wi, and the thermometer diode D2 has a width W2 less than Wi. The voltage Vd is applied to the thermometer transducer. Three electrical configurations are then possible: a first configuration where both thermometer diodes are activated simultaneously: the total electrical current Id flowing through the thermometer transducer then has a maximum value Id>max. It is possible, in another configuration, to activate only the single diode D1, leading to a current total electrical current Id having a value Id4 less than Id>max; and, in a last configuration, to activate only the single diode D2, leading to a total electrical current Id having a value Id>2 less than Id>max and Idji: Id>2 < Id,i < Id>max.

[0050] Note that, in these three electrical configurations, the current density flowing through the thermometer transducer has the same value Jd, so that the thermal resolution ATmin of the thermometer transducer remains constant. Therefore, the thermal detector 1 exhibits performance in terms of sensitivity and speed that can be adjusted according to the intended application, without degrading the thermal resolution ATmin of the thermometer transducer.

[0051] Thus, in the case of detecting a low incident flux, the sensitivity of the thermal detector 1 will be prioritized over its speed: the aim will therefore be to increase the self-heating ge of the absorbing membrane 30, and therefore the value of the total electric current Id: the reading circuit 12 will bias only diode DI or preferably both diodes DI and D2 simultaneously. Conversely, in the case of detecting a moving scene, the speed of the thermal detector 1 will be prioritized: the aim will then be to limit the self-heating ge of the absorbing membrane 30, and therefore the value of the total electric current Id: the reading circuit 12 will preferably bias only diode D2. A compromise can, however, be sought between the sensitivity and the speed of the thermal detector 1: therefore, the reading circuit may bias diode DI alone.It therefore appears that the thermal detector 1 exhibits great versatility in its performance in terms of sensitivity and speed, by controlling the activation of the thermometer diodes independently of each other, without this resulting in a degradation of the thermal resolution ATmin of the thermometer transducer.

[0052] Figure 2A is a schematic and partial cross-sectional view of a thermal detector 1 according to an alternative embodiment. Figure 2B partially illustrates the equivalent electrical circuit of the thermometer diodes D1, D2 and the reading circuit 12.

[0053] The thermal detector 1 differs from that of [Fig.1B] essentially in that the thermometer diodes D1, D2 have identical widths, and in that a single polarization conductive track 33c allows the cathodes of the thermometer diodes D1, D2 to be brought to the same electrical potential.

[0054] Thus, the thermometer transducer includes a diode Dl of width Wl, and a diode D2 of width W2 equal to Wl (but the widths Wl and W2 can of course be different).

[0055] Furthermore, the same conducting bias track 33c extends over one of the thermal insulation arms, and comes into electrical contact with the cathode of diode Dl and of that of diode D2. On the other hand, another conducting bias track 33a makes electrical contact with the anode of diode D1, and another conducting bias track 33b is in electrical contact with the anode of diode D2. Thus, the reading circuit 12, which here includes switches connected in series, one with diode D1 and the other with diode D2, allows selective activation of diode D1 alone, diode D2 alone, or both diodes D1 and D2.

[0056] Other electrical arrangements are obviously possible, such as providing the same conducting bias track 33c for the anodes of diodes D1 and D2, and two other conducting bias tracks 33a, 33b separate for the cathodes.

[0057] The thermal detector 1 according to this embodiment has better thermal insulation of the absorbing membrane 30, insofar as one of the thermal insulation arms 25 does not have a polarization conductive track 33, which improves the performance of the thermal detector 1 in terms of thermal insulation and therefore sensitivity.

[0058] Figure 3A is a schematic and partial cross-sectional view of a thermal detector 1 according to another embodiment. Figure 3B partially illustrates the equivalent electrical circuit of the thermometer diodes D1, D2 and the reading circuit 12.

[0059] The thermal detector 1 differs from that of [Fig.1B] essentially in that the thermometer diodes D1, D2 are mounted in reverse (always in parallel), and in that only two conducting bias tracks 33a, 33b allow a potential difference to be applied to the thermometer diodes.

[0060] The thermometer transducer is therefore formed of two diodes Dl and D2 mounted in reverse (antisymmetric mounting), in the sense that here the cathode of Dl and the anode of D2 are connected to the same node of the electrical circuit and are therefore brought to the same electrical potential, and in that the anode of Dl and the cathode of D2 are connected to another same node of the electrical circuit.

[0061] Since the thermometer diodes D1 and D2 are mounted back-to-back, they have different widths. In this example, the width W1 is greater than the width W2.

[0062] Furthermore, a single biasing conductive track 33a extends into a thermally insulated arm 25 and makes electrical contact with the anode of diode D1 and the cathode of diode D2. Another biasing conductive track 33b extends into a different thermally insulated arm and makes electrical contact with the cathode of D1 and the anode of diode D2. Other electrical configurations are obviously possible. Two switches allow the bias voltage Vd to be applied to diodes D1 and D2 in either direction of the circuit.

[0063] During operation, a bias voltage Vd is applied to the diodes connected in parallel. Depending on the sign of the voltage Vd, one of the diodes is in the conducting state. while the other is in the blocked state. Thus, we can have an electrical configuration where diode DI alone is in the conducting state, so that the total electrical current Id has a value Idji, and another electrical configuration where diode D2 alone is in the conducting state, so that the total electrical current Id has a value Id>2, different from Id4 due to the difference between the widths Wi and W2.

[0064] The thermal detector 1 according to this embodiment has even higher thermal insulation of the absorbing membrane, insofar as only two of the four thermal insulation arms each have a polarization conductive track 33, which improves the performance of the thermal detector 1 in terms of thermal insulation and therefore sensitivity.

[0065] Figure 4A is a schematic, partial top view of a thermal detector 1 according to another embodiment. Figure 4B illustrates the evolution of the self-heating gain gÆ of the absorbing membrane 30 as a function of the cumulative width Wtot of the activated thermometer diodes.

[0066] The thermal detector 1 is adapted here to absorb in the sub-terahertz band, for example between 100 GHz and 11 Hz. The operating temperature can be around 80 K so as to minimize the thermal resolution of the thermometer diodes.

[0067] The insulating layer 21 located between the reflector 21 and the high-impedance surface 23 has a thickness of approximately 1 µm (see [Fig. 1A]). The high-impedance surface 23 is made of an aluminum layer. The absorbing membrane is spaced approximately 2.5 µm from the high-impedance surface 23.

[0068] The absorber 36 (metallic dipole) is made here of niobium. The coupling between the high-impedance surface 23 and the absorber 36 ensures the absorption of terahertz radiation. In this example, where the absorption spectrum is desired to be centered on the frequency of 425 GHz, the absorber 36 has a width of 6 pm and a length of 265 pm. These dimensions facilitate the integration of several thermometer diodes D1, D2. Furthermore, the bias conductive tracks 33 are made of TiN, and the insulating layers 31, 32, 34 are made of amorphous silicon.

[0069] The absorbing membrane 30 here has a rectangular shape with a high length-to-width ratio. Four thermal insulation arms 25 hold the absorbing membrane 30 in place. Two thermometer diodes D1, D2 are located in a central part of the absorbing membrane 30. The absorber 36 has a width less than the 6 pm indicated previously, relative to the thermometer diodes D1 and D2.

[0070] The thermometer diodes D1, D2 are made of crystalline silicon with a thickness of, for example, between 20nm and 300nm, for example equal to about 50nm. The n+ doped lateral region is doped with phosphorus, and the p+ doped lateral region is doped with boron. The doping level here is greater than 10¹⁹ cm³ to ensure good ohmic contact. The doping level (n-type or p-type) of the central region is between 10 and 10 cm⁻¹, for example, 10 cm⁻¹. Furthermore, the length of the central region is preferably between 1 and 1 Opm, for example, 5 pm, to optimize thermal resolution.

[0071] Under these conditions, the thermometer diodes D1, D2 exhibit a thermal resolution ATmin, for a bias voltage Vd of approximately 1.02V (corresponding to a current density of 2nA / pm), of approximately 0.15mK, and a current temperature coefficient (CTC) greater than 20% / K for a current density of approximately 2nA / pm. The total thermal resistance Rth is therefore equal to 80 MK / W. It is then possible to determine the self-heating gÆ of the absorbing membrane 30, for power absorbed in the spectral band of InW.

[0072] Figure 4B illustrates an example of the variation of the self-heating ge as a function of the cumulative width Wtot of the temperature diodes activated by the reading circuit. The total width corresponds to the sum of the widths of the activated temperature diodes. It can be seen that the self-heating ge remains close to unity for a total width Wm of less than approximately 7 pm. Furthermore, for a total width of the biased diodes of approximately 14.2 pm, thermal runaway occurs, which is obviously undesirable since it can lead to degradation of the absorber membrane materials. This thermal runaway occurs when the sum of the absorbed power and the power generated by Joule heating in the absorber membrane is too great to be dissipated by the thermal insulation arms.

[0073] Thus, by adjusting the total width Wtot by selectively activating the thermometer diodes biased at a voltage Vd, it is possible to adjust the self-heating gÆ to favor the sensitivity and / or speed of the thermal detector, without degrading the thermal resolution ATmin of the thermometer diodes.

[0074] Specific embodiments have just been described. Various variants and modifications will be apparent to those skilled in the art.

Claims

Demands

1. A thermal detector (1) of electromagnetic radiation, comprising: • a reading substrate (10), including a reading circuit (12); • an absorbing membrane (30), suspended above the reading substrate (10) and thermally insulated from it, and including a thermometer transducer electrically connected to the reading circuit (12) and biased by the latter with a voltage Vd; • characterized in that the thermometer transducer is formed of several thermometer diodes (D1, D2) connected in parallel; • in that the reading circuit (12) is adapted to activate the thermometer diodes (D1, D2) selectively;• and in that the thermometer diodes (D1, D2) and the reading circuit (12) are configured so as to present at least the following two electrical configurations: a first configuration where a total electric current Id flowing in the thermometer transducer biased at the voltage Vd has a first value Idji; and a second configuration where the total electric current Id has a second value Id>2 different from Id>i.;

2. Thermal detector (1) according to claim 1, wherein the thermometer diodes (D1, D2) are lateral diodes each comprising two doped lateral regions and a central region located, in a plane parallel to the main plane of the absorbing membrane (30), between the two doped lateral regions.

3. Thermal detector (1) according to claim 2, wherein the thermometer diodes are made of the same crystalline semiconductor material.

4. A thermal detector (1) according to any one of claims 1 to 3, wherein the absorbing membrane (30) is held suspended by thermal insulation arms (25) extending to anchoring pillars (24), and wherein polarization conductive tracks extend from the anchoring pillars (24) to passing through the thermal insulation arms (25) to come into electrical contact with the thermometer diodes (D1, D2).

5. Thermal detector (1) according to any one of claims 1 to 4, wherein the thermometer diodes are mounted symmetrically, and each has an identical or not identical width from one thermometer diode to another.

6. Thermal detector (1) according to claims 4 and 5, wherein a single conductive polarization track is in electrical contact with an anode or cathode of at least two thermometer diodes connected in a symmetrical arrangement.

7. Thermal detector (1) according to any one of claims 1 to 4, wherein the thermometer diodes are mounted antisymmetrically, and each has a different width from one thermometer diode to another.

8. Thermal detector (1) according to claims 4 and 7, wherein a single conductive polarization track is in electrical contact with an anode and a cathode of at least two thermometer diodes connected in an antisymmetric arrangement.

9. Thermal detector (1) according to any one of claims 1 to 8, wherein the reading circuit (12) includes at least one switch or at least one two-way switch connected to the thermometer diodes to activate the thermometer diodes selectively.

10. Thermal detector (1) according to any one of claims 1 to 8, adapted to detect terahertz radiation or infrared radiation.

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