A HIGH-BANDWIDTH THERMOELECTRIC THIN-FILM UV, VISIBLE LIGHT AND INFRARED RADIATION SENSOR AND A METHOD FOR MANUFACTURING THEREOF

Abstract

The invention relates to UV, visible light and infrared radiation sensors, in particular to high-bandwidth thin-film electromagnetic radiation sensors, operating using the principle of thermoelectric effect. According to one embodiment the sensor comprises: a thermoelectric active layer, an electrode layer one and an electrode layer two, wherein the electrode layer one is located below the thermoelectric active layer and the electrode layer two is located above the thermoelectric active layer, whereby the sensor is designed so that the thermal gradient can be created and the electrical voltage can be measured perpendicular to the thermoelectric active layer, between the electrode layer one and the electrode layer two, wherein the material of the thermoelectric active layer is low molecular weight organic compound, selected so that its thermal conductivity would be less than 1 W/(m K{circumflex over ( )}2), Seebeck coefficient modulus would be greater than 100 μV/K and its molecular weight is less than 900 Da.

Claims

1.-10. (canceled)

11. A thermoelectric thin-film UV, visible light and infrared radiation sensor, having signal rise time <10 ns and fall time <1 μs, comprising: a 100-1000 nm thick thermoelectric active layer, an electrode layer one and an electrode layer two, wherein the electrode layer one is located below the thermoelectric active layer and the electrode layer two is located above the thermoelectric active layer, whereby the sensor is designed so that the thermal gradient can be created and the electrical voltage can be measured perpendicular to the thermoelectric active layer, between the electrode layer one and the electrode layer two, wherein the material of the thermoelectric active layer is low molecular weight organic compound, selected from the group consisting of metal phthalocyanines, perylene derivatives and polyacene derivatives, so that its thermal conductivity would be less than $1\frac{W}{m{K}^2},$ Seebeck coefficient modulus would be greater than $100\frac{\mu V}{K}$ and its molecular weight is less than 900 Da.

12. The sensor according to claim 11, further comprising an absorption layer, located on the electrode layer two.

13. The sensor according claim 11, wherein the electrode layer one has a thickness greater than 100 μm, so that it can serve also as a conductive substrate.

14. The sensor according claim 11, wherein the electrode layer one and the electrode layer two are made of copper, aluminium, gold, silver or their alloys.

15. The sensor according claim 11, wherein the sensor further comprises a substrate having $\mathrm{thermal}\mathrm{conductivity}>10\frac{W}{m{K}^2}$ and electrical resistivity >15 Ω/square, to which the electrode one is attached along its surface, which is opposite to the electrode one surface to which the thermoelectric active layer is deposited.

16. A method for the manufacture of the thermoelectric thin-film UV, visible light and infrared radiation sensor having signal rise time <10 ns and fall time <1 μs, according to any one of claims 1-5, comprising the following steps: providing an electrode one having an electrical resistance of less than 15 Ω/square; depositing a 100-1000 nm thick thermoelectric active layer on the top of the electrode one by thermal evaporation in vacuum; wherein the material of the thermoelectric active layer is selected from the group consisting of metal phthalocyanines, perylene derivatives and polyacene derivatives; providing an electrode two having an electrical resistance of less than 15 Ω/square, on top of the thermoelectric active layer by physical vapour deposition in vacuum; and optional step of (iv) applying an absorption layer on top of the electrode two.

17. The method according to claim 16, wherein the material, selected for the electrode layer one and the electrode layer two is selected from the group consisting of copper, aluminium, gold, silver and their alloys.

18. The method according to claim 16, the method further comprising the step (i′) of providing a substrate having $\mathrm{thermal}\mathrm{conductivity}>10\frac{W}{m{K}^2}$ and resistivity >15 Ω/square, the substrate on which the electrode one is deposited by physical vapour deposition along its surface, which is opposite to the electrode one surface to which the thermoelectric active layer is to be deposited or is deposited.

19. The method according to claim 16, the method further comprising the step (v) of applying an electrically non-conductive insulation layer of necessary shape on the electrode one before step (ii) to define the conductive area of the electrode one.

Description

SHORT DESCRIPTION OF DRAWINGS

[0012] FIG. 1 shows structural scheme of one embodiment of the invention as well as direction of sensor operation, where 1 is a heat conducting substrate of the sensor, 2—an electrode layer one, 3—a thermoelectric active layer, 4—an electrode layer two.

[0013] FIG. 2 is a schematic representation of a cross-section of another embodiment of the sensor, where 1 is a heat conducting substrate of the sensor, 2—an electrode layer one, 3—a thermoelectric active layer, 4—an electrode layer two, 5—optional absorption layer.

[0014] FIG. 3 is a schematic view of a cross-section of the sensor on an electrically conductive substrate, wherein 6—is an electrode layer one having thickness greater than 100 μm, and serving as an electrically conductive substrate, 3—a thermoelectric active layer, 4—an electrode layer two, 5—optional absorption layer.

[0015] FIG. 4 is a diagram, showing graph of a signal of the sensor without an absorption layer, irradiated with a 10 ns pulse of 1064 nm, pulse peak power 1 kW.

[0016] FIG. 5 is a diagram, showing graph of a signal of the sensor without an absorption layer, irradiated with a 10 ns pulse of 430 nm impulse, pulse peak power 2.3 kW.

[0017] FIG. 6 is a diagram, showing values of the sensor signal integral for different irradiance wavelengths as a function of pulse peak power; integration time 0.2 μs.

[0018] FIG. 7 is a schematic representation of sensor manufacture on electrically non-conductive (electrical resistivity >15 Ω/square) substrate, where: a—sensor substrate

[00003]$\left(\mathrm{thermal}\mathrm{conductivity}>10\frac{W}{m{K}^2}\right),$

b—sensor substrate with applied electrode layer one, c—with applied thermoelectric active layer, d—applied the electrode layer two, f—applied optional light absorption layer.

[0019] FIG. 8: is a schematic representation of another embodiment of the sensor manufacture on electrically conductive substrate, where: a—a thermally conductive

[00004]$\left(\mathrm{thermal}\mathrm{conductivity}>10\frac{W}{m{K}^2}\right)$

and electrically conductive (electrical resistivity 15 Ω/square) substrate, b—substrate with applied insulating layer, c—with applied thermoelectric active layer, d—applied the electrode layer two, f—applied optional light absorption layer.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The operation of the sensor according to the present invention is based on the thermoelectric effect perpendicular to the plane of the thin-film, i.e. in the direction of the smaller dimension of the thermoelectric active layer, in which also the electrical voltage is measured. The existing sensor structure allows to develop active area sensors of different sizes, which active area is not limited to the size of the sensor structure, as it is in the known MEMS systems.

[0021] The proposed high-bandwidth thermoelectric thin-film UV, visible light and infrared radiation sensor (FIG. 1) comprising: a 100-1000 nm thick organic thermoelectric active layer 3, an electrode layer one 2 and an electrode layer two 4. The electrode layer one 2 is located below the thermoelectric active layer 3 and the electrode layer two 4 is located above the thermoelectric active layer 3. The sensor is designed so that the thermal gradient is created and the electrical voltage can be measured perpendicular to the thermoelectric active layer 3—between the electrode layer one 2 and the electrode layer two 4. The material of the thermoelectric active layer 3 is low molecular weight organic compound, selected so that its thermal conductivity would be less than

[00005]$1\frac{W}{m{K}^2},$

Seebeck coefficient modulus would be greater than

[00006]$100\frac{\mu V}{K}$

and its molecular weight is less than 900 Da. Thermal resistance and Seebeck coefficient of layer 3 determine the response to the generated heat from absorbed radiation. The thermal resistance must be sufficiently high to produce high enough thermal gradient, therefore thickness of organic thermoelectric active layer 3 need to be greater than 100 nm if the thermal conductivity is close to

[00007]$1\frac{W}{m{K}^2}.$

On the other hand, the thicker the layer, the lower the bandwidth, so the thickness of organic thermoelectric active layer 3 should not exceed 1000 nm.

[0022] According to another embodiment (FIG. 2), the sensor may comprise an absorption layer 5, located on the electrode layer two 4. According to yet another embodiment, the electrode layer one 2 has a thickness greater than 100 μm, so that it can serve also as a substrate. The electrode layer one 2 and the electrode layer two 4 can be made of copper, aluminium, gold, silver or other appropriate material, such as their alloys. The copper is preferred material due to its high thermal conductivity and relatively low cost. The thermoelectric active layer 3 according to the invention may be a metal phthalocyanines, such as copper or zinc phthalocyanine, perylene derivative, or polyacene derivatives, such as pentacene or tetrathiotetracene.

[0023] The sensor according to yet another embodiment (FIG. 3) may comprise a substrate 1 having

[00008]$\mathrm{thermal}\mathrm{conductivity}>10\frac{W}{m{K}^2}$

and electrical resistivity >15 Ω/square, to which the electrode one 2 is attached along its surface, which is opposite to the electrode one 2 surface to which the thermoelectric active layer 3 is deposited.

[0024] The UV/visible light/infrared radiation falling on the sensor heats up the electrode layer two 4 (FIG. 1), creating a thermal gradient in the thermoelectric active layer 3 perpendicular to the plane of the thermoelectric active layer 3. A thermal gradient is formed and the electrical voltage is measured in the direction of the smallest dimension. The thermoelectric effect in the thermoelectric active layer 3 produces an electrical voltage in the direction of the thermal gradient. As the thermal conductivity of the thermoelectric active layer 3 is low

[00009]$\left(<1\frac{W}{m{K}^2}\right)$

and Seebeck coefficient modulus is high

[00010]$\left(>100\frac{\mu V}{K}\right),$

the generated thermal gradient is high enough to produce ample electric voltage by TE effect. The voltage further could be amplified with high performance amplifiers. As the thermoelectric active layer 3 has a thickness of less than 1 μm, the propagation of heat between the electrodes 2 and 4 is rapid, enabling the development of a high-bandwidth radiation sensor.

[0025] FIGS. 4 and 5 show the signal of a sensor whose thermoelectric active layer 3 is made of tetrathiotetracene by irradiating it with a 10 ns laser pulse of 1064 nm. It could be seen that the length of the increasing front of the signal is 10 ns, while the decreasing time constants are below 1 μs.

[0026] The method for the manufacture of the high-bandwidth thermoelectric thin-film UV, visible light and infrared radiation sensor, comprising the following steps: (i) providing an electrode one 2 having an electrical resistance of less than 15 Ω/square; ii depositing a 100-1000 nm thick thermoelectric active layer 3 on the top of the electrode one 2 by thermal evaporation in vacuum; (iii) providing an electrode two 4 having an electrical resistance of less than 15 Ω/square, on top of the thermoelectric active layer 3 by physical vapour deposition in vacuum; and optional step of (iv) applying an absorption layer 5 on top of the electrode two 4.

[0027] According to another embodiment the method further comprises the step (i′) of providing a substrate 1 having a

[00011]$\mathrm{thermal}\mathrm{conductivity}>10\frac{W}{m{K}^2}$

and resistivity >15 Ω/square, the substrate 1 on which the electrode one 2 is deposited by physical vapour deposition along its surface, which is opposite to the electrode one 2 surface to which the thermoelectric active layer 3 is to be deposited or is deposited.

[0028] According to yet another embodiment the method further comprises the step (v) of applying an electrically non-conductive insulation layer of necessary shape on the electrode one 2 before step (ii) to define the conductive area of the electrode one 2.

[0029] In the manufacture of the sensor, thin-film technologies in vacuum are used. An electrode one 2 of the required shape (FIG. 7b) is applied to the heat-conducting substrate 1 (FIG. 7a), if it is not electrically conductive. Applying the electrode comprises mainly of one or two steps. If necessary, in the first step a electrode adhesion to substrate-improving layer such as Cr layer, is applied to the substrate. In the second step, the electrode layer itself is applied. By thermal evaporation in vacuum method, an organic thermoelectric layer 3 having a thickness 100-1000 nm is applied to the electrode (FIG. 7c). The electrode layer two 4 is applied to the thermoelectric layer 3 (FIG. 7d). An optional radiation absorption layer 5 is applied over the electrode two 4 (FIG. 7f).

[0030] When a thermally conductive and electrically conductive substrate 6 is used (FIG. 8a), which also serves as an electrode layer one 2, an insulating layer 7 of necessary shape can be applied thereto (FIG. 8b). The thermoelectrically active layer 3 of organic materials having a thickness of 100-1000 nm is applied over the opened electrode one 2 portion by thermal evaporation in vacuum method (FIG. 8c). The electrode layer two 4 is applied to the thermoelectrically active layer (FIG. 8d). An optional radiation absorption layer 5 is applied over the electrode layer two 4 (FIG. 8f).

[0031] Examples of Implementation of the Invention

[0032] Table 1 provides a list of potentially suitable materials for sensor productions. Sensor could be made by various combinations of materials, but the main properties that organic thermoelectric materials should have are low thermal conductivity of formed thin film

[00012]$\left(<1\frac{W}{m{K}^2}\right)$

and high Seebeck coefficient modulus

[00013]$\left(>100\frac{\mu V}{K}\right).$

Preferred electrode material is copper due to its high thermal conductivity and relatively low cost.

TABLE-US-00001 TABLE 1 List of materials, that could be used to produce the sensor Electrode one Organic TE active layer Electrode two Aluminium Copper phthalocyanine Aluminium Cu Zinc phthalocyanine Cu Gold Other metal phthalocyanine derivatives Gold Silver Pentacene Silver Alloys Tetrathiotetracene Alloys Other polyacene derivatives Perylene derivatives

[0033] Some examples are detailed below. Example 1—sensor on electrically non-conducting substrate. The electrode layer one 2 consisting of Cr layer with a thickness of 10 nm and a Cu layer with a thickness of 190 nm is applied to the Si substrate 1. Cr is used to improve adhesion. A 500 nm thick tetrathiotetracene layer is applied over the electrode layer one 2 as the thermoelectric active layer 3. A 100 nm thick Cu electrode layer two 4 is applied above it.

[0034] Example 2—sensor on the conductive substrate. On the Cu substrate 6, an insulating layer 7 is formed from the photoresist SU-8 by a lithographic method. Above the exposed Cu layer, a 500 nm thick tetrathiotetracene layer is applied as the thermoelectric active layer 3. A 100 nm thick Cu electrode layer two 4 is applied above it.

[0035] The proposed sensor has a relatively simple design with operating principle (thermal gradient and electric voltage) in smallest dimension perpendicular to the thin film plane using organic TE active materials with low thermal conductivity. No buffer layer is required in these sensors where electric field is measured perpendicular to the plane of the thin film. Another and very important advantage of the invention over the sensors known to date is that it is possible to make a large-area sensor without reducing its high-bandwidth. Moreover, such a sensor is almost one order faster than the prior art ones due to the different voltage measurement direction.

SOURCES OF INFORMATION

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