Lithium niobate crystal pyroelectric sensor

Abstract

The invention discloses a lithium niobate crystal pyroelectric sensor, and belongs to the field of infrared detection. The sensor uses a lithium niobate crystal as a pyroelectric response sensitive element of an infrared radiation heat signal. The lithium niobate crystal sensitive element is subjected to reduction treatment, and meanwhile, the pyroelectric coefficient is remarkably improved, and 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 niobate 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 niobate 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 niobate crystals. Background Technology

[0002] Pyroelectric infrared (PIR) detection is a type of thermal detector 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 are widely used in intrusion detection sensors, flame detection, gas detection, spectrometers, medical equipment, infrared thermal imaging, infrared guidance, and many other fields.

[0003] Lead zirconate titanate-based ceramic materials are among the most widely used and technologically mature materials in commercial human infrared detection, possessing a high pyroelectric coefficient (2×10⁻⁶). -4 C·m -2 K -1 ~3×10 -4 C·m -2 K -1 Lead zirconate titanate (LZT) ceramics offer advantages such as a high Curie temperature and the ability to operate without a bias electric field. However, their extremely high dielectric constant (typically 1000–3000) limits device response speed. Furthermore, LZT ceramics contain 60%–70% lead, posing significant environmental risks.

[0004] Lithium tantalate crystal is the most widely used single-crystal material in pyroelectric sensors such as flame detection and spectral detection, with a pyroelectric coefficient of approximately 1.9 × 10⁻⁶. -4 C·m -2 K -1 Lithium niobate has a high Curie temperature of 665 ℃ and a relatively low dielectric constant (~40), exhibiting excellent temperature stability and the advantage of being able to grow large-size single crystals via the Czochralski method. Lithium niobate crystals have a similar crystal structure to lithium tantalate crystals, but with a higher Curie temperature and lower preparation cost. However, the pyroelectric coefficient of lithium niobate crystals is only 0.8 × 10⁻⁶. -4 C·m -2 ·K -1 The inherent defects of lithium niobate crystals severely limit their application in pyroelectric effects, thus they have long been neglected. Lithium niobate crystals are rich in intrinsic defects, allowing for significant manipulation of many of their properties through compositional changes, doping engineering, and valence state control. However, current research on the manipulation of the pyroelectric effect of lithium niobate crystals is limited, and existing manipulation processes are complex. Even after optimization, the pyroelectric performance of lithium niobate crystals still cannot meet practical application requirements. Therefore, there is an urgent need for a lead-free, environmentally friendly pyroelectric sensor to replace lead zirconate titanate ceramics and find applications in the field of infrared detection. Summary of the Invention

[0005] The main objective of this invention is to provide a lithium niobate crystal pyroelectric sensor that uses a reduced lithium niobate 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 niobate 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 niobate crystal, the two lithium niobate 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 niobate crystal pyroelectric sensor.

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

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

[0010] 2. Lithium niobate wafer reduction treatment: The lithium niobate wafer is subjected to reduction treatment. Preferably, the pyroelectric coefficient of the lithium niobate wafer is increased after reduction treatment, while the resistivity 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 niobate wafer using magnetron sputtering to obtain a lithium niobate 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 niobate pyroelectric sensor: A lithium niobate crystal sensing element, a field-effect transistor, and an infrared narrowband filter are packaged into a lithium niobate crystal pyroelectric sensor. Preferably, the two lithium niobate crystals are connected in reverse series. Alternatively, a single sensing element can operate independently.

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

[0014] 1. The sensor's sensing element is made of lithium niobate crystal material, which does not contain lead and is more environmentally friendly.

[0015] 2. After reduction treatment, the pyroelectric coefficient of lithium niobate crystal sensing elements can be improved, and the dielectric constant and dielectric loss of lithium niobate crystals are small, resulting in a significant increase in the response voltage and sensitivity of the prepared lithium niobate crystal sensor.

[0016] 3. The resistivity of the lithium niobate crystal sensing element is reduced through reduction treatment. When connected to the field-effect transistor, no impedance matching resistor is required, which reduces the number of internal components and soldering points of the sensor, reduces noise, and lowers costs. Detailed Implementation

[0017] 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.

[0018] Example 1:

[0019] This embodiment 1 discloses a lithium niobate crystal pyroelectric sensor, the specific steps of which are as follows:

[0020] (1) Preparation of lithium niobate wafers: Lithium niobate crystals were oriented, cut and ground to obtain lithium niobate 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 niobate crystals. The ground lithium niobate wafers do not require polishing.

[0021] (2) Reduction treatment of lithium niobate wafers: The ground lithium niobate wafers are placed in a tube furnace with a controllable atmosphere. After evacuation, argon gas is introduced into the quartz tube and reduced at 450 °C for 30 min.

[0022] (3) Preparation of sensitive element electrodes: Electrodes were deposited on the two surfaces of the treated lithium niobate 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.

[0023] (4) Fabrication of a lithium niobate pyroelectric sensor: Two lithium niobate crystal sensing elements are connected in reverse series to 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 a lithium niobate crystal pyroelectric sensor.

[0024] (5) Device performance: When the lithium niobate 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 110.25 mV, 51.12 mV and 20.33 mV respectively.

[0025] Example 2:

[0026] This embodiment 2 discloses a lithium niobate crystal pyroelectric sensor, the specific steps of which are as follows:

[0027] (1) Preparation of lithium niobate crystal wafers: Lithium niobate crystals were oriented, cut and ground to obtain lithium niobate wafers with dimensions x×y×z=3.00 mm×5.00 mm×0.05 mm, where x, y, and z are the crystallographic directions of the lithium niobate crystal. The ground lithium niobate wafers do not require polishing.

[0028] (2) Lithium niobate wafer reduction treatment: The ground lithium niobate 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 400 ℃ for 40 min.

[0029] (3) Preparation of sensitive element electrodes: Electrodes were deposited on the two surfaces of the treated lithium niobate 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.

[0030] (4) Fabrication of a lithium niobate pyroelectric sensor: Two lithium niobate 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. 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 the lithium niobate crystal pyroelectric sensor.

[0031] (5) Device performance: When the lithium niobate 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 101.46 mV, 37.94 mV and 12.18 mV respectively.

[0032] Example 3:

[0033] This embodiment 3 discloses a lithium niobate crystal pyroelectric sensor, the specific steps of which are as follows:

[0034] (1) Preparation of lithium niobate wafers: Lithium niobate crystals are oriented, cut and ground to obtain lithium niobate 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 niobate crystals. The ground lithium niobate crystals do not require polishing.

[0035] (2) Reduction treatment of lithium niobate wafers: The ground lithium niobate 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 450 °C for 60 min.

[0036] (3) Electrode preparation of sensing element: Electrodes were deposited on the two surfaces of the treated lithium niobate wafer by magnetron sputtering. The electrode material was nickel metal and the electrode thickness was about 100 nm, thus preparing a single lithium niobate crystal sensing element.

[0037] (4) Fabrication of a lithium niobate pyroelectric sensor: A single lithium niobate 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 niobate crystal pyroelectric sensor.

[0038] (5) Device performance: When the lithium niobate 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 72.29 mV, 29.26 mV and 6.44 mV respectively.

[0039] Comparative Example 1:

[0040] This comparative example discloses the test results of a lithium niobate crystal pyroelectric sensor of the same composition that has not undergone reduction treatment. The difference between this example and Example 1 is as follows:

[0041] (1) Sensor structure: The impedance of the lithium niobate 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 Example 1, the resistivity of the lithium niobate crystal sensing element is reduced after reduction treatment, eliminating the need for a matching resistor. The internal structure of the sensor is simpler, and the manufacturing cost is lower.

[0042] (2) Device performance: Under an ambient temperature of 27 ℃, the pyroelectric response voltages of the lithium niobate crystal pyroelectric sensor without reduction treatment, after 10 times signal amplification, were 20.98 mV, 9.00 mV, and 1.93 mV, respectively, for the infrared radiation signal from a 37 ℃ blackbody at operating frequencies of 0.1 Hz, 1.0 Hz, and 3.0 Hz. Compared with the sensor test results in Example 1, the pyroelectric response voltage has been significantly improved.

[0043] 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 niobate crystal pyroelectric sensor, employing a reduced-treated lithium niobate 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 as follows: The lithium niobate 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 niobate crystal pyroelectric sensor according to claim 1, characterized in that, The lithium niobate crystal sensor uses a lithium niobate crystal as the pyroelectric response sensitive element for infrared radiation thermal signals.

3. The lithium niobate crystal pyroelectric sensor according to claim 2, characterized in that, The lithium niobate crystal sensing element is subjected to reduction treatment to improve the pyroelectric coefficient and optimize the sensor performance.

4. The lithium niobate crystal pyroelectric sensor according to claim 2, characterized in that, The lithium niobate 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.

5. A lithium niobate 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.

6. The lithium niobate crystal pyroelectric sensor according to claim 1, characterized in that, The two lithium niobate 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.

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

8. A lithium niobate crystal pyroelectric sensor according to claim 6, characterized in that, By allowing two sensitive elements to receive signals sequentially, the sensor's output signal can be improved.

9. A pyroelectric sensor using a lithium niobate crystal as described in claims 1-8, characterized in that, Lithium niobate crystals can be used in infrared signal detection, human infrared detection, and spectral testing. These applications include, but are not limited to, medical and health care, security monitoring, smart homes, and gas detection.