Tungsten-doped vanadium oxide thin film for thermal meter type infrared detector and preparation method of tungsten-doped vanadium oxide thin film

Abstract

The invention discloses a tungsten-doped vanadium oxide thin film for a thermal meter type infrared detector and a preparation method of the tungsten-doped vanadium oxide thin film. The tungsten doping proportion of the tungsten-doped vanadium oxide thin film is changed in a gradient mode in the direction perpendicular to the thin film, multiple layers of vanadium oxide thin films with the tungsten doping concentration changing from low to high or from high to low in a stepped mode are sequentially grown on the surface of a substrate, and then annealing is conducted to enable the concentration gradient of doped tungsten atoms to become smooth. And the integrated gradient tungsten-doped vanadium oxide film is formed. The gradient tungsten-doped vanadium oxide thin film has high TCR in a wide temperature window, is applied to a thermometer type infrared detector as a heat-sensitive material, can greatly improve the sensitivity of the infrared detector, and can be used in complex application scenes.

Description

Technical Field

[0001] The present invention relates to a highly sensitive thermal material for a micro-thermometer infrared detector, and in particular to a gradient tungsten-doped vanadium oxide thin film material and a preparation method thereof, and belongs to the intersecting field of sensors, micro-electromechanical systems and material science. Background Art

[0002] A micro-calorimeter infrared detector is an infrared detector based on micro-electromechanical technology. Since it does not require a complex cooling system to detect and image infrared bands, this type of detector is widely used in infrared imaging cameras and has a high market share in the civilian field. A micro-calorimeter infrared detector usually contains a cavity and a bracket structure. There is a metal reflector at the bottom of the cavity. This cavity structure is used to enhance the absorption of infrared light and convert the energy of infrared light into heat energy, which increases the temperature of the structure. A thin film of thermosensitive material is prepared above the cavity to detect temperature changes through changes in its resistance, thereby realizing the detection of infrared light. The side length of a typical detector unit is from a dozen to several hundred microns. In addition, the detector chip also includes structures such as the device's electrodes, interconnects, and readout circuits, while the complete detection system is mainly composed of the detector chip, optical system, and packaging structure.

[0003] An important factor affecting the sensitivity of the micro uncooled calorimeter infrared detector is the temperature sensitivity of the thermosensitive material on the cavity. Traditionally, there are two types of thermosensitive materials used in commercial calorimeter infrared detectors: vanadium oxide (VO x ) and amorphous silicon (α-Si). The first pyroelectric infrared detector using vanadium oxide was successfully developed by Honeywell in the United States in the 1980s, while amorphous silicon was not successfully commercialized by a French company until the late 1990s. The vanadium oxide (VO x ) can generally reach 2%-3%. Compared with α-Si, using VO x The detector has more advantages in performance, because VO x The material has low noise and high TCR, making it an ideal sensitive material for detectors.

[0004] Single crystal vanadium oxide material (VO 2 ) is a classic metal-insulator phase change material. It undergoes an insulator-metal phase transition at around 67 degrees Celsius, converting from a low-temperature insulating state to a high-temperature metallic state, and its resistance will be greatly reduced. It has a very high TCR in a relatively narrow temperature window near the phase transition temperature. However, its property that its resistance changes only drastically near the phase transition temperature also restricts its further application. Commercial VO xThe material is an amorphous material in which vanadium oxides of various valences coexist. It has a relatively stable TCR (2%-3%) over a wide temperature range and has no phase transition near 67 degrees Celsius.

[0005] The phase transition temperature of single crystal vanadium oxide can be adjusted by doping. Different doping elements and different doping methods can make the phase transition temperature and performance of the doped film change favorably, which is of great value for improving the sensitivity of calorimeter-type infrared detectors. Summary of the invention

[0006] The object of the present invention is to prepare a doped vanadium oxide film used in a micro-calorimeter type infrared detector, which has the advantage of having high temperature sensitivity in a wide temperature range.

[0007] If tungsten is doped into a single crystal vanadium oxide material, the phase transition temperature of the material can be reduced by about 25 degrees Celsius for every 1% atomic ratio of tungsten element doping. Based on this, the present invention proposes a gradient tungsten-doped vanadium oxide film, which makes the film resistance change dramatically in a larger temperature window by doping different concentrations of tungsten at different positions, thereby achieving a higher TCR in the full temperature range. Compared with traditional VO x The gradient doped film of the present invention has a TCR of more than 7%, which can significantly improve the sensitivity of the infrared detector.

[0008] The temperature sensitivity of vanadium oxide films is usually characterized by TCR (temperature coefficient of resistance), which is defined as follows:

[0009]

[0010] Where R is resistance and T is temperature. The physical meaning of TCR is the ratio of the change in resistance when the temperature changes to the resistance at this temperature. The larger the TCR, the more sensitive the material's resistance is to temperature.

[0011] As a classic metal-insulator phase change material, vanadium oxide has a very dramatic change in resistance when a phase change occurs. The resistance change can exceed 4 orders of magnitude in a temperature window of less than 10 degrees Celsius near 67 degrees Celsius, and the TCR of the material is very large at this time. At the same time, adding tungsten to vanadium oxide can reduce the phase change temperature of the material. For every 1% atomic ratio of tungsten added, the phase change temperature of vanadium oxide can be reduced by about 25 degrees Celsius. Based on this fact, the present invention proposes to prepare a gradient tungsten-doped vanadium oxide film, so that the tungsten doping ratio has a gradient in the direction perpendicular to the film, that is, the phase change temperature of the vanadium oxide layer at different thickness positions is different, so that the entire film can have a high TCR in a wide temperature range.

[0012] Specifically, the technical solution of the present invention is as follows.

[0013] A gradient tungsten-doped vanadium oxide film used in a calorimeter-type infrared detector, wherein the tungsten doping ratio changes gradiently in a direction perpendicular to the film, is obtained by the following preparation method: first, a multilayer vanadium oxide film with a tungsten doping concentration changing in a step-like manner from low to high or from high to low is grown in sequence on the surface of a substrate, and then annealing is performed to make the concentration gradient of the doped tungsten atoms smoother, thereby forming an integrated gradient tungsten-doped vanadium oxide film.

[0014] In actual use, the gradient tungsten-doped vanadium oxide film needs to be grown on the support structure of a calorimeter-type infrared detector, and the commonly used material for the support of such infrared detectors is silicon nitride. Therefore, the growth substrate of the gradient tungsten-doped vanadium oxide film is usually a silicon nitride substrate. For detectors using other support materials, the substrate material can be changed accordingly.

[0015] The above-mentioned gradient tungsten-doped vanadium oxide film can use PVD (physical vapor deposition) technology to grow vanadium oxide films with different tungsten doping concentrations during the growth process of each film. Specifically, PLD (pulsed laser deposition), magnetron sputtering and other technologies can be used. The target material used can be a tungsten-doped vanadium oxide target material or a tungsten-vanadium alloy target material with different doping ratios. It is also possible to grow tungsten-doped vanadium oxide films with different concentrations by chemical vapor deposition methods such as ALD (atomic layer deposition). At this time, the atomic ratio of doping can be controlled by controlling the number of cycles of tungsten oxide and vanadium oxide during the atomic layer deposition cycle.

[0016] The above-mentioned gradient tungsten-doped vanadium oxide film has different tungsten doping concentration and thickness for each layer of the film. Specifically, tungsten-doped vanadium oxide films are deposited on the substrate in sequence from low to high doping concentrations. The higher the doping concentration, the smaller the thickness of the corresponding layer of film deposited. When using PVD growth, targets with different tungsten doping concentrations are required to grow film layers with different doping ratios. When using ALD growth, the tungsten doping ratio can be controlled simply by adjusting the number of cycles of tungsten and vanadium. The thickness of the gradient tungsten-doped vanadium oxide film is generally 50 to 500nm, and the tungsten doping concentration can gradually change from 0.3% to 4% atomic ratio. 4 to 5 layers of thin films with step-like changes in tungsten doping ratios can be prepared first, and then thermal annealing can be performed.

[0017] The annealing process of the above-mentioned gradient tungsten-doped vanadium oxide film is to make the distribution of tungsten atoms smoother, thereby forming a uniform gradient tungsten-doped vanadium oxide film. After the film deposition is completed, the vertical distribution of the tungsten doping concentration is relatively steep, and the corresponding tungsten doping ratio of each layer is stepped. After annealing, the tungsten atoms will diffuse under the action of the concentration gradient, making the vertical distribution of tungsten smooth. After the annealing is completed, a gradient tungsten-doped vanadium oxide film can be obtained. The heating rate during annealing is preferably 15 to 30°C / min, heating to 450 to 500°C, maintaining for 10 to 15 minutes, and then naturally cooling to room temperature. Annealing is preferably carried out in an oxygen-containing atmosphere, with an oxygen flow rate of 2.5 to 4.5 sccm and a pressure of 4 to 5 Pa.

[0018] The gradient tungsten-doped vanadium oxide film of the present invention is applied as a thermosensitive material to a calorimeter-type infrared detector, which can greatly improve the sensitivity of the infrared detector.

[0019] The technical effects of the present invention are as follows:

[0020] A gradient tungsten-doped vanadium oxide film is used to replace the single-concentration tungsten-doped vanadium oxide film commonly used in calorimeter-type infrared detectors to achieve a higher TCR in a larger temperature window, thereby greatly improving the sensitivity of the corresponding infrared detector.

[0021] Compared with a single-ratio tungsten-doped vanadium oxide film, the gradient tungsten-doped vanadium oxide film used in the present invention can be regarded as the accumulation of multiple layers of tungsten-doped vanadium oxide film layers with different doping ratios, and the tungsten doping concentration is smoothly distributed from low to high. Since each 1% of tungsten atom doping can reduce the phase transition temperature of vanadium oxide by about 25 degrees Celsius, within a wide temperature range, the corresponding layer in the gradient tungsten-doped vanadium oxide film is in the phase change process. Since the vanadium oxide film in the phase change process will produce a higher TCR, the gradient tungsten-doped vanadium oxide film proposed in the present invention has a higher TCR within a very wide temperature window. In contrast, the vanadium oxide film with a single tungsten doping ratio only has a higher TCR near the phase transition temperature, which is difficult to use in actual complex application scenarios. Compared with commercial VO x Compared with conventional materials, the gradient tungsten-doped vanadium oxide film proposed in the present invention has a higher TCR in the full temperature range and has a significant advantage in sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic cross-sectional diagram of the calorimeter type infrared detector of the present invention.

[0023] In the figure: 1 - gradient tungsten-doped vanadium oxide film; 2 - cavity support; 3 - reflector; 4 - substrate.

[0024] Figure 2This is a TCR variation curve of the gradient tungsten-doped vanadium oxide film prepared in an embodiment of the present invention during the temperature rise and fall process. DETAILED DESCRIPTION

[0025] The present invention will be further described below by way of examples in conjunction with the accompanying drawings, but the scope of the present invention is not limited in any way.

[0026] like Figure 1 As shown, the gradient tungsten-doped vanadium oxide film proposed in the present invention is a thermosensitive material used in a calorimeter-type infrared detector. The gradient tungsten-doped vanadium oxide film 1 is located on a cavity bracket 2, and a reflector 3 is provided on a substrate 4 in the cavity of the calorimeter-type infrared detector.

[0027] The preparation method of the gradient tungsten-doped vanadium oxide film is specifically described in detail using magnetron sputtering growth as an example. The use of other PVD and ALD technologies only differs in the specific growth of each layer, and the doping ratio and thickness of each layer remain unchanged, and the annealing process remains unchanged.

[0028] 1) Prepare the substrate material, usually silicon nitride, which is consistent with the support material of the target infrared detector;

[0029] 2) The target material used is a tungsten-vanadium alloy target material, which is made by doping a small amount of tungsten into vanadium. Each doping ratio corresponds to a target material with a doping ratio, and the target material needs to be replaced when growing films with different doping ratios.

[0030] 3) Magnetron sputtering sequentially grows four layers of vanadium oxide with different tungsten doping concentrations, and the specific parameters of each layer are as follows: the first layer, 0.3-0.5% atomic ratio W doped vanadium oxide, film thickness 35-45nm; the second layer, 1.0-1.3% atomic ratio W doped vanadium oxide, film thickness 20-30nm; the third layer, 2.0-2.5% atomic ratio W doped vanadium oxide, film thickness 12-18nm; the fourth layer, 3.0-4.0% atomic ratio W doped vanadium oxide, film thickness 8-10nm. The growth temperature is room temperature, the sputtering power is 50-60W, and the growth rate is 3-4nm per minute. A mixed process gas of oxygen and argon is introduced during the growth, and the pressure of the magnetron sputtering chamber is 0.6-0.8Pa. The thickness of the above layers can also be increased proportionally according to demand.

[0031] 4) Annealing to form a uniform gradient tungsten-doped vanadium oxide film. The annealing procedure is: heating from room temperature to 450 degrees Celsius for 20 minutes, maintaining for 10 minutes, and naturally cooling to room temperature. During annealing, 3.5 sccm of oxygen is introduced and the pressure is maintained at 4.5 Pa.

[0032] from Figure 2 It can be seen that the TCR of the gradient tungsten-doped vanadium oxide film is greater than 5% during the heating and cooling process between 0-40°C, while the existing VO xThe TCR of the material is between 2-3% (see reference: [1] Yu Lijing, Tang Libin, Yang Wenyun, et al. Research progress of uncooled infrared detectors (invited) [J]. Infrared and Laser Engineering, 2021, 50(01): 71-85.).

[0033] The embodiments described above are not intended to limit the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention is defined by the scope of the claims.

Claims

1. A gradient tungsten-doped vanadium oxide film, characterized in that: The tungsten doping ratio changes gradiently in a direction perpendicular to the film, and the film material is obtained by the following preparation method: first, a multilayer vanadium oxide film with a tungsten doping concentration changing in a step-like manner from low to high or from high to low is grown in sequence on the surface of the substrate, and then the concentration gradient of the doped tungsten atoms is smoothed by annealing to form an integrated gradient tungsten-doped vanadium oxide film.

2. The gradient tungsten-doped vanadium oxide film according to claim 1, characterized in that: The substrate is a silicon nitride substrate.

3. The gradient tungsten-doped vanadium oxide film according to claim 1, characterized in that: The thickness of the gradient tungsten-doped vanadium oxide film is 50-500nm, and the tungsten doping concentration gradually changes from 0.3% to 4% atomic ratio.

4. The gradient tungsten-doped vanadium oxide film according to claim 1, characterized in that: Each layer of tungsten-doped vanadium oxide film is grown by physical vapor deposition or chemical vapor deposition. The target material used in the physical vapor deposition method is a tungsten-doped vanadium oxide target material or a tungsten-vanadium alloy target material with different doping ratios. The chemical vapor deposition method controls the doping atomic ratio by controlling the number of cycles of tungsten oxide and vanadium oxide during the deposition cycle.

5. The gradient tungsten-doped vanadium oxide film according to claim 4, characterized in that: The physical vapor deposition method adopts laser pulse deposition or magnetron sputtering; the chemical vapor deposition method adopts atomic layer deposition.

6. The gradient tungsten-doped vanadium oxide film according to claim 1, characterized in that: First, four layers of vanadium oxide films with different tungsten doping concentrations are grown on the substrate from bottom to top in sequence: the first layer, a 0.3-0.5 atomic ratio tungsten doped vanadium oxide film, with a thickness of 35-45nm; the second layer, a 1.0-1.3 atomic ratio tungsten doped vanadium oxide film, with a thickness of 20-30nm; the third layer, a 2.0-2.5 atomic ratio tungsten doped vanadium oxide film, with a thickness of 12-18nm; the fourth layer, a 3.0-4.0 atomic ratio tungsten doped vanadium oxide film, with a thickness of 8-10nm; then the temperature is increased for annealing, and the gradient tungsten-doped vanadium oxide film is obtained after natural cooling.

7. The gradient tungsten-doped vanadium oxide film according to claim 1, characterized in that: The annealing temperature is 450-500°C, and the annealing time is 10-15 minutes.

8. The gradient tungsten-doped vanadium oxide film according to claim 1, characterized in that: Annealing is performed in an oxygen-containing atmosphere, wherein the oxygen flow rate is 2.5-4.5 sccm and the pressure is maintained at 4-5 Pa.

9. Use of the gradient tungsten-doped vanadium oxide film as claimed in any one of claims 1 to 8 as a thermosensitive material in a calorimeter type infrared detector.

10. A pyrometer type infrared detector, comprising a substrate, a cavity support on the substrate, a reflector arranged on the substrate in the cavity, and a heat-sensitive material located on the cavity support, characterized in that: The thermosensitive material is the gradient tungsten-doped vanadium oxide film according to any one of claims 1 to 8.

Images