Lithium tantalate crystal pyroelectric sensor

Abstract

The invention discloses a lithium tantalate crystal pyroelectric sensor, and belongs to the field of infrared detection. The sensor uses a lithium tantalate crystal as a pyroelectric response sensitive element of an infrared radiation heat signal. After the lithium tantalate crystal sensitive element is subjected to reduction treatment, the pyroelectric coefficient is not reduced, but the resistivity is reduced. The sensor adopts a structure that double sensitive elements are reversely connected in series to compensate the environment temperature, and adopts narrow-band optical filters with different transmission wavelengths to filter signal light, so as to meet the sensing of a signal with a specific wavelength or a specific object. The lithium tantalate crystal pyroelectric sensor meets the detection requirement of infrared radiation heat signals, an impedance matching resistor is not needed when the sensitive element is connected with the field-effect tube, and the lithium tantalate crystal pyroelectric sensor has the advantages of being simple in structure, high in sensitivity, fast in response, low in noise and environmentally friendly and is suitable for various infrared detection scenes.

Description

Technical Field

[0001] This invention relates to applications in the field of infrared radiation signal detection, specifically to a pyroelectric infrared sensor using lithium tantalate crystals. Background Technology

[0002] Pyroelectric infrared (PIR) detection is a type of thermal detection that converts temperature changes caused by varying infrared radiation signals into electrical signals based on the pyroelectric effect of the sensitive element. Compared to other thermal detectors, PIR detectors offer advantages such as fast response, high responsivity, wide operating frequency range, and no need for cooling. They have been widely used in civilian fields such as human motion detection, gas analysis, and temperature measurement, and also play a crucial role in military technologies such as infrared night vision and target tracking.

[0003] Lithium tantalate crystals are one of the most widely used pyroelectric materials, with a pyroelectric coefficient of approximately 1.9 × 10⁻⁶. -4 C·m -2 ·K -1 With a Curie temperature as high as 665 ℃, lithium tantalate exhibits stable physicochemical properties, is easy to process, and can be fabricated into large-size single crystals using the melt pulling method. Based on the advantages of lithium tantalate crystals, such as high pyroelectric coefficient, low dielectric constant and dielectric loss, high Curie temperature, and high temperature stability, it has been widely used in non-infrared spectroscopic gas detectors, flame detection, non-contact temperature measurement, and spectrometers.

[0004] Lithium tantalate crystals are rich in intrinsic defects, allowing for significant manipulation of many of their properties through compositional changes, doping engineering, and valence state modulation. However, research on the modulation of the pyroelectric properties of lithium tantalate crystals is currently limited. Optimization of the detection performance of lithium tantalate crystal pyroelectric sensors has been achieved through techniques such as thinning of the sensing element, depositing an infrared absorption layer on the sensing element, and redesigning the internal structure of the sensor. However, these methods increase the complexity and cost of the sensor fabrication process. Lithium tantalate crystals have extremely high resistivity, typically around 10⁻⁶. 14 The impedance of lithium tantalate crystals (LiTAN) is much higher than that of the input impedance of a field-effect transistor (FET). This necessitates the use of a high-precision, high-resistance external load resistor to achieve impedance matching with the preamplifier when connecting the LiTAN to the FET. This not only increases the cost of the sensor but also conflicts with the technical approach of reducing detector noise. Therefore, it is necessary to optimize the pyroelectric properties of LiTAN material. Without reducing the pyroelectric coefficient of LiTAN, its resistivity should be reduced, the external matching resistor eliminated, and the internal structure of the sensor simplified, resulting in superior performance for the LiTAN crystal sensor. Summary of the Invention

[0005] The main objective of this invention is to provide a lithium tantalate crystal pyroelectric sensor that uses a reduced lithium tantalate crystal as the sensing element, which can meet the detection requirements of infrared radiation thermal signals, and does not require a matching resistor when the lithium tantalate crystal sensing element is connected to the field-effect transistor.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] After reducing the lithium tantalate crystal, the two lithium tantalate crystal sensing elements are connected in reverse series. The signal is initially amplified using a field-effect transistor. A narrowband filter can also be used to filter the detection signal to obtain a lithium tantalate crystal pyroelectric sensor.

[0008] The specific implementation steps of the method of the present invention are as follows:

[0009] 1. Preparation of lithium tantalate wafers: Lithium tantalate crystals are oriented and cut along the crystallographic x, y, z directions and then ground without polishing to obtain lithium tantalate wafers.

[0010] 2. Lithium tantalate wafer reduction treatment: The lithium tantalate wafer is subjected to reduction treatment. Preferably, the resistivity of the lithium tantalate wafer after reduction treatment is reduced to match the input impedance of the field-effect transistor.

[0011] 3. Electrode fabrication for the sensing element: Electrodes are deposited on both surfaces of a lithium tantalate wafer using magnetron sputtering to obtain a lithium tantalate crystal sensing element. Preferably, the electrode material is a metal such as gold, silver, copper, nickel, aluminum, or chromium, or an alloy of these metals. Alternatively, conductive materials such as indium tin oxide, antimony tin oxide, zinc aluminum oxide, or silver oxide can be used.

[0012] 4. Fabrication of a lithium tantalate pyroelectric sensor: A lithium tantalate crystal sensing element, a field-effect transistor, and an infrared narrowband filter are packaged into a lithium tantalate crystal pyroelectric sensor. Preferably, the two lithium tantalate crystals are connected in reverse series. Alternatively, a single sensing element can operate independently.

[0013] Compared with existing pyroelectric infrared sensors based on lithium tantalate crystals, the present invention has the following advantages:

[0014] 1. After reduction treatment, the resistivity of the lithium tantalate crystal sensing element is reduced. When connected to the field-effect transistor, no external impedance matching resistor is required, resulting in a simpler internal structure and lower manufacturing cost.

[0015] 2. The number of internal components and solder joints in lithium tantalate sensors is reduced, resulting in lower noise. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0017] Example 1:

[0018] This embodiment 1 discloses a lithium tantalate crystal pyroelectric sensor, the specific steps of which are as follows:

[0019] (1) Preparation of lithium tantalate wafers: Lithium tantalate crystals were oriented, cut and ground to obtain lithium tantalate wafers with dimensions x×y×z=3.00 mm×5.00 mm×0.08 mm, where x, y, and z are the crystallographic orientations of the lithium tantalate crystals. The ground lithium tantalate wafers do not require polishing.

[0020] (2) Reduction treatment of lithium tantalate wafers: The ground lithium tantalate wafers are placed in a tube furnace with a controllable atmosphere, and the vacuum degree inside the quartz tube is kept at (10±1) Pa by evacuation. After reduction treatment at 400 ℃ for 60 min.

[0021] (3) Electrode preparation of sensitive elements: Electrodes were deposited on the two surfaces of the treated lithium tantalate wafer by magnetron sputtering. The electrode material was nickel metal and the electrode thickness was about 100 nm. Two sensitive elements were prepared by arranging them side by side along the y direction of the crystal.

[0022] (4) Fabrication of the lithium tantalate pyroelectric sensor: Two lithium tantalate crystal sensing elements are connected in reverse series, and the two sensing elements receive signals sequentially. A 2SK2751 field-effect transistor is used for signal amplification and impedance conversion. The two output terminals of the sensing elements are connected to the drain of the field-effect transistor and ground, respectively. An infrared narrowband filter with a transmission wavelength of 7 μm to 10 μm is used as the transmission window and packaged into a TO-5 structure to obtain the lithium tantalate crystal pyroelectric sensor.

[0023] (5) Device performance: When the lithium tantalate crystal pyroelectric sensor is used at an ambient temperature of 27 ℃, the infrared radiation signal of a 37 ℃ blackbody is amplified by 10 times at working frequencies of 0.1 Hz, 1.0 Hz and 3.0 Hz. The measured pyroelectric response voltages are 30.55 mV, 28.12 mV and 17.28 mV respectively.

[0024] Example 2:

[0025] This embodiment 2 discloses a lithium tantalate crystal pyroelectric sensor, the specific steps of which are as follows:

[0026] (1) Preparation of lithium tantalate crystal wafers: Lithium tantalate crystals were oriented, cut and ground to obtain lithium tantalate wafers with dimensions x×y×z=3.00 mm×5.00 mm×0.08 mm, where x, y, and z are the crystallographic orientations of the lithium tantalate crystals. The ground lithium tantalate wafers do not require polishing.

[0027] (2) Reduction treatment of lithium tantalate wafers: The ground lithium tantalate wafers are placed in a tube furnace with a controllable atmosphere, and the vacuum degree inside the quartz tube is maintained at (10±1) Pa by evacuation. The reduction treatment is carried out at 600 ℃ for 60 min.

[0028] (3) Electrode preparation of sensitive elements: Electrodes were deposited on the two surfaces of the treated lithium tantalate wafer by magnetron sputtering. The electrode material was nickel metal and the electrode thickness was about 100 nm. Two sensitive elements were prepared by arranging them side by side along the y direction of the crystal.

[0029] (4) Fabrication of a lithium tantalate pyroelectric sensor: Two lithium tantalate crystal sensing elements are connected in reverse series. One sensing element is covered, and the other is used to detect infrared radiation signals. A 2SK2751 field-effect transistor is used for signal amplification and impedance conversion. The two output terminals of the sensing element are connected to the drain of the field-effect transistor and ground, respectively. An infrared narrowband filter with a transmission wavelength of 7 μm to 10 μm is used as the transmission window and packaged into a TO-5 structure to obtain a lithium tantalate crystal pyroelectric sensor.

[0030] (5) Device performance: When the lithium tantalate crystal pyroelectric sensor is used at an ambient temperature of 27 ℃, the infrared radiation signal of a 37 ℃ blackbody is amplified by 10 times at working frequencies of 0.1 Hz, 1.0 Hz and 3.0 Hz. The measured pyroelectric response voltages are 27.28 mV, 25.21 mV and 16.63 mV respectively.

[0031] Example 3:

[0032] This embodiment 3 discloses a lithium tantalate crystal pyroelectric sensor, the specific steps of which are as follows:

[0033] (1) Preparation of lithium tantalate wafers: Lithium tantalate crystals are oriented, cut and ground to obtain lithium tantalate wafers with dimensions x×y×z=3.0 mm×3.0 mm×0.1 mm, where x, y and z are the crystallographic directions of lithium tantalate crystals. The ground lithium tantalate crystals do not require polishing.

[0034] (2) Reduction treatment of lithium tantalate wafers: The ground lithium tantalate wafers were placed in a corundum crucible and completely covered with lithium carbonate powder. Then the crucible was placed in a muffle furnace and reduced at 500 °C for 60 min.

[0035] (3) Electrode preparation of sensing element: Electrodes were deposited on the two surfaces of the treated lithium tantalate wafer by magnetron sputtering. The electrode material was nickel metal and the electrode thickness was about 100 nm, thus preparing a single lithium tantalate crystal sensing element.

[0036] (4) Fabrication of a lithium tantalate pyroelectric sensor: A single lithium tantalate crystal sensing element detects infrared radiation. A 2SK2751 field-effect transistor is used for signal amplification and impedance conversion. The two output terminals of the sensing element are connected to the drain of the field-effect transistor and ground, respectively. A narrow-band infrared filter with a transmission wavelength of 7 μm to 10 μm is used as the transmission window and packaged into a TO-5 structure to obtain a lithium tantalate crystal pyroelectric sensor.

[0037] (5) Device performance: When the lithium tantalate crystal pyroelectric sensor is used at an ambient temperature of 27 ℃, the infrared radiation signal of a 37 ℃ blackbody is amplified by 10 times at working frequencies of 0.1 Hz, 1.0 Hz and 3.0 Hz. The measured pyroelectric response voltages are 25.78 mV, 24.89 mV and 15.77 mV respectively.

[0038] Comparative Example 1:

[0039] This comparative example discloses the test results of a lithium tantalate crystal pyroelectric sensor of the same composition that has not undergone reduction treatment. The difference between this example and Examples 1-3 is as follows:

[0040] (1) Sensor structure: The impedance of the lithium tantalate crystal sensing element without reduction treatment is greater than the input impedance of the sensor preamplifier circuit. When connected to the field-effect transistor, a high-precision chip resistor with a resistance of 100 GΩ is required to detect the output signal. In Examples 1 to 3, the resistivity of the lithium tantalate crystal sensing element is reduced after reduction treatment, eliminating the need for a matching resistor. The internal structure of the sensor is simple, and the manufacturing cost is lower.

[0041] (2) Device performance: Under an ambient temperature of 27 ℃, the pyroelectric response voltages of the lithium tantalate crystal pyroelectric sensor without reduction treatment, after 10-fold signal amplification, were 27.22 mV, 25.73 mV, and 17.93 mV, respectively, to the infrared radiation signal from a 37 ℃ blackbody at operating frequencies of 0.1 Hz, 1.0 Hz, and 3.0 Hz. The sensor test results in Examples 1-3 are consistent with these results, indicating comparable sensor performance.

[0042] Although the preferred embodiments of the present invention have been disclosed above, and the description is quite specific and detailed, it should not be construed as limiting the scope of the present invention. For those skilled in the art, various modifications, improvements, and substitutions can be made without departing from the inventive concept. These include changing the transmission wavelength of the window filter, changing the packaging method, changing the connection method of the sensing elements, changing the sensor operating mode, and using different sensing element sizes, different numbers of sensing elements, different electrode sizes, different window sizes, etc., to create various reasonable modifications. All of these should be considered within the scope of protection of the present invention.

Claims

1. A lithium tantalate crystal pyroelectric sensor, employing a reduced-treated lithium tantalate crystal as the sensing element for detecting infrared radiation signals. It can operate with a single sensing element working independently or with two sensing elements connected in reverse series. The sensor utilizes a field-effect transistor for initial signal amplification. The sensor can employ a narrowband filter to filter the detected signal. Its characteristics are: The lithium tantalate crystal pyroelectric sensor can meet the detection requirements of infrared radiation thermal signals, and no matching resistor is required when the sensitive element is connected to the field-effect transistor.

2. The lithium tantalate crystal pyroelectric sensor according to claim 1, characterized in that, The lithium tantalate crystal sensor uses a lithium tantalate crystal as the pyroelectric response sensitive element for infrared radiation thermal signals.

3. The lithium tantalate crystal pyroelectric sensor according to claim 2, characterized in that, The lithium tantalate crystal sensing element undergoes a reduction process, which lowers its resistivity. When connected to a field-effect transistor, it does not require an external impedance matching resistor.

4. The lithium tantalate crystal pyroelectric sensor according to claim 1, characterized in that, Narrowband filters with different transmission wavelengths are used to filter the signal light in order to meet the requirements for detecting specific wavelength signals or specific objects.

5. A lithium tantalate crystal pyroelectric sensor according to claim 1, characterized in that, The two lithium tantalate crystal sensing elements are connected in reverse series to eliminate the influence of external factors such as ambient temperature fluctuations and vibrations on the sensor.

6. A lithium tantalate crystal pyroelectric sensor according to claim 5, characterized in that, One of the sensitive elements can be masked, while the other sensitive element is used for detection.

7. A lithium tantalate crystal pyroelectric sensor according to claim 5, characterized in that, By allowing two sensitive elements to receive signals sequentially, the sensor's output signal can be improved.

8. A pyroelectric sensor using a lithium tantalate crystal as described in claims 1-7, characterized in that, Lithium tantalate crystals can be used in infrared signal detection, human infrared detection, spectral testing, flame detection, and other applications, including but not limited to medical and health care, security monitoring, smart home, and gas detection.