Hemt humidity sensor for respiratory monitoring and method of manufacturing and use thereof

Abstract

The application discloses a HEMT humidity sensor for breath monitoring, a preparation method and application thereof, and belongs to the field of semiconductor humidity sensors. The preparation method comprises the following steps: step 1, mesa etching of a GaN-based heterojunction material epitaxial wafer is carried out by using a stage power etching method; step 2, etching of a source-drain electrode buried region is carried out by using a scheme of first plasma treatment and then wet etching; step 3, a gold-free ohmic contact manufacturing scheme is adopted; step 4, a cage-shaped monomer containing a mercapto group and a monomer containing an olefin bond are dissolved in a mixed solvent of tetrahydrofuran and methanol as a skeleton material and a photocatalyst; step 5, a small amount of precursor liquid is drop-coated on the surface of a sensitive gate region of the HEMT device, and irradiated under ultraviolet light for 15-30 minutes; and step 6, the same solvent system is used for wetting. The HEMT humidity sensor made of the material as a sensitive material has a sensitivity of an order of magnitude in a full humidity range, and the sensor can well detect breath and distinguish breath frequency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of humidity-sensitive elements and its preparation, and particularly relates to an ion gel gate high electron mobility transistor humidity-sensitive element and a preparation method and application thereof. BACKGROUND

[0002] The home health system relying on sensing technology is a key foundation for building a smart medical system and solving medical and livelihood problems. Respiratory function monitoring, as an important part of the home health system, is an important way to non-invasively evaluate human health status. Exhaled gas humidity detection has important significance in the fields of mental and physical state monitoring, lung function evaluation, and non-invasive respiratory diagnosis.

[0003] Existing respiratory detection mainly relies on lung function testing instruments, polysomnography (PSG), and end-tidal carbon dioxide concentration monitoring (ETCO2) detection methods. These methods can accurately record / evaluate the respiratory pattern / lung function of individuals in clinical practice. However, due to the complexity of the detection process, high universal threshold, and the need for professional personnel to analyze and process data, the advantages of respiratory analysis are difficult to fully play in daily life. In recent years, in order to seek a low-threshold, wearable real-time respiratory monitoring method, a large number of respiratory monitoring methods based on different principles have emerged, such as force-sensitive, temperature-sensitive, sound-sensitive, and humidity-sensitive methods. These methods each have advantages and disadvantages, among which the humidity-sensitive method based on exhaled gas humidity detection principle has the advantages of direct efficiency, high recognition, and less external interference, and has been widely valued and intensively studied.

[0004] In order to develop the application of humidity sensors in the field of respiratory monitoring and lung function evaluation, it is necessary to further improve the performance indicators of the sensor. On the one hand, the respiratory cycle of a person at rest is generally 3-4 s, and can be as short as 2 s in excessive ventilation. In order to achieve accurate detection of the amount and rate of change of water molecules, the humidity sensor must have high sensitivity and response recovery speed within 1 s. On the other hand, the relative humidity of exhaled gas is about 70-90% RH, so how to improve the high-humidity stability of the humidity sensor is also an important problem that needs to be solved. The solution to these problems can significantly improve the performance of the sensor and lay a technical foundation for its application expansion in the field of respiratory monitoring and lung function evaluation.

[0005] For respiratory monitoring, researchers based on different sensing mechanisms, build a variety of material systems, and through different device structures to improve the performance of humidity sensors. However, at present, humidity sensors are difficult to have high sensitivity, fast response, and high stability of sensing performance at the same time. The limited response of the humidity-sensitive device under the stimulation of high-humidity gas flow can only meet the requirements of respiratory frequency monitoring, and most of the test curves are in the metastable state type (c), or even the non-stable state type (d). Figure 1 c), even the non-stable state type (d).Figure 1 d). In order to achieve accurate measurement of the indicators such as breath depth, flow rate, tidal volume, etc., the output value needs to quickly reach a steady state Figure 1 b). Therefore, designing and constructing a high-sensitivity, fast-response and high-stability humidity sensor is the key to effective breath monitoring. Under the stimulation of exhaled high humidity flow, the sensor can achieve high change rate, quickly reach a steady state (I: stable type → ideal type), accurately measure various indicators in the breath, and work in a high humidity environment for a long time to achieve real-time monitoring all day long. SUMMARY The purpose of the present application is to solve the performance problems of the humidity-sensitive element in human breath monitoring. By in-situ synthesizing a high-performance ionic gel humidity-sensitive film in the sensitive gate region of a high electron mobility transistor (HEMT), a high-sensitivity, fast-response and high-humidity-stability polymer-based humidity-sensitive element based on an AlGaN / GaN high electron mobility transistor suitable for breath frequency and breath pattern monitoring and a preparation method thereof are provided.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0007] A preparation method of an ionic gel gate-based HEMT humidity-sensitive device,

[0008] Step one ( Figure 2 a): GaN-based heterojunction wafer mesa etching: after the clean GaN-based heterojunction wafer is developed by photolithography, the sample is subjected to mesa isolation etching using Cl-based gas and the process parameters of the inductively coupled plasma device optimized in the early stage. A smaller power is used for etching at the end to reduce surface damage and roughness, and finally chemical solution cleaning treatment is performed;

[0009] Step two ( Figure 2 b): Source-drain electrode buried region etching: after the wafer is developed by photolithography, the source-drain buried region of the epitaxial layer is etched by inductively coupled plasma method. After dry etching, the sample etching damage is further reduced by using the scheme of first etching the GaN surface by plasma and then etching by wet method, so as to maintain the smoothness of the etched surface;

[0010] Step three ( Figure 2 c): Drain ohmic contact electrode fabrication: electron beam evaporation method is used to deposit metal in the electrode window formed by photolithography, and the excess metal is stripped by acetone immersion ultrasonic stripping; good ohmic contact is formed by using rapid thermal annealing process;

[0011] Step four ( Figure 3): the thiol-containing and the olefin-containing prepolymers and a small amount of photocatalyst are dissolved in a mixed solvent of tetrahydrofuran and methanol; a small amount of precursor solution is drop-coated on the surface of the sensitive gate region of the HEMT device, and is subjected to in-situ cross-linking reaction under ultraviolet light; finally, rinsing is performed with the same solvent system to remove the catalyst and unreacted raw materials.

[0012] Compared with the prior art, the present application has the following advantages:

[0013] The present application adopts the ion gel high-performance humidity-sensitive material to modify the sensitive gate region of the depletion-mode HEMT transistor, and combines the high sensitivity, high chemical stability of the HEMT device and the advantages of the ion gel in terms of high moisture adsorption and desorption and high moisture stability, so that the ion gel gate HEMT humidity-sensitive element prepared has high sensitivity and high stability, and can be used to continuously monitor the human exhaled gas. BRIEF DESCRIPTION OF DRAWINGS In order to more clearly illustrate the technical solutions of the embodiments of the present application, the present application will be described in detail below in combination with the drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0014] Figure 1 It is a schematic diagram of the breathing monitoring curve type based on the humidity sensor; Figure 2 It is a schematic diagram of the preparation process of the humidity-sensitive device according to the present application; Figure 3 It is a process diagram of the in-situ preparation of the humidity-sensitive film in the gate region of the humidity-sensitive device according to the present application;

[0015] Figure 4 It is a humidity absorption performance diagram of the humidity-sensitive device according to the present application;

[0016] Figure 5 It is a simulation result diagram of the humidity-sensitive device according to the present application for breathing detection. DETAILED DESCRIPTION The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0017] Example 1

[0018] The HEMT structure used in the present application is as follows Figure 2As shown, including a 20 nm thick silicon oxide layer, a 2 µm thick undoped gallium nitride layer, a 20 nm thick aluminum gallium nitride layer with an aluminum content of 25%, source and drain electrodes of Ti / Al / Ni / TiN, and an electrode protection layer of SiO2.

[0019] The specific steps are as follows:

[0020] Step one: surface pretreatment of HEMT epitaxial wafer: the cut epitaxial wafer is placed in an acetone solution and ultrasonically cleaned for 10 minutes, the epitaxial wafer is taken out and placed in anhydrous ethanol and ultrasonically cleaned for 10 minutes, then the epitaxial wafer is placed in deionized water and ultrasonically cleaned for 10 minutes to remove the glue on the surface of the epitaxial wafer and the organic matter attached to the surface; then the epitaxial wafer is taken out and immersed in a dilute hydrochloric acid solution with a volume ratio of 1:10 for 3 minutes to remove the oxide film on the surface of the epitaxial wafer, and finally the epitaxial wafer is placed in deionized water and ultrasonically cleaned for 10 minutes to remove the residual reagent. The surface of the epitaxial wafer is blown dry with a nitrogen gun for use;

[0021] Step two: after the clean AlGaN / GaN epitaxial wafer is developed by photolithography, the sample is mesa-isolated etched using a Cl-based gas with the process parameters of the inductively coupled plasma device optimized in the early stage;

[0022] Step three: after the epitaxial wafer is developed by photolithography, the source and drain buried regions of the epitaxial layer are etched by inductively coupled plasma method, and the etching depth is 350 nm;

[0023] Step four: Ti (20 nm) / Al (100 nm) / Ni (45 nm) / TiN (55 nm) is sequentially deposited in the electrode window formed by photolithography by using an electron beam evaporation method, and the excess metal is ultrasonically stripped by acetone immersion.

[0024] Example 2

[0025] The preparation of the ion gel material used in the application is as follows: 50.0 mg of mercaptopropyl polyhedral oligomeric silsesquioxane, 255.0 mg of vinylhexylimidazole bromide salt and 4.0 mg of benzoin dimethyl ether are dissolved in a mixed solvent of 2 mL of tetrahydrofuran and 6 mL of methanol (the feeding ratio of mercaptopropyl polyhedral oligomeric silsesquioxane to vinylhexylimidazole bromide salt is 1:12); 2.5 ul of the precursor solution is dropped on the surface of the sensitive gate region of the HEMT device, and is irradiated under ultraviolet light for 20-30 minutes to perform in-situ crosslinking reaction; finally, the same solvent system is used for rinsing to remove the catalyst and unreacted raw materials.

[0026] Example 3

[0027] The sensitive element performance test is carried out according to the method disclosed in the art, and the specific method is as follows: the above-mentioned humidity sensitive element is detected by using Keithley 2450 SourceMeter (Keithley Instruments Corporation), different relative humidity environments are prepared by saturated salt solution, and the relative humidity includes 11% (LiCl), 33% (MgCl2), 54% (Mg(NO3)2), 75% (NaCl), 85% (KCl) and 95% (KNO3). Under the action of 1 volt direct current, the current between the source electrode and the drain electrode of the element prepared in Example 2 in the state of equilibrium under different relative humidity is read. The test is carried out on the hygroscopic characteristic curve of the element when the test element is converted between 11% and 95% relative humidity Figure 4 ), and the current-time change curve of the element under the exhaled air flow at the nose of the human body Figure 5 ).

[0028] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed in the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for preparing a HEMT humidity sensor for respiratory monitoring, characterized in that, It comprises the following steps: Step 1. Adopting stage power etching method to carry out mesa etching of GaN-based heterojunction material epitaxial wafer; GaN-based heterojunction epitaxial wafer mesa etching: after the clean GaN-based heterojunction epitaxial wafer is developed by photolithography, the sample is subjected to mesa isolation etching by using Cl-based gas and the process parameters of the inductively coupled plasma device optimized in the early stage, and finally the etching is carried out by using smaller power to reduce surface damage and roughness, and finally chemical solution cleaning treatment is carried out; Step 2. Adopting the method of first plasma treatment and then wet etching to carry out source and drain electrode buried region etching; Source and drain electrode buried region etching: after the epitaxial wafer is developed by photolithography, the epitaxial layer source and drain buried region is etched by inductively coupled plasma method; After dry etching, the scheme of first etching the surface of GaN by plasma treatment and then etching by wet etching is used to further reduce the etching damage of the sample, so as to keep the etching surface smooth and smooth; Step 3. Adopting gold-free ohmic contact method to make electrode; drain ohmic contact electrode manufacturing: adopting electron beam evaporation method to deposit metal in the electrode window formed by photolithography, and soaking the excess metal in acetone and ultrasonic stripping; using rapid thermal annealing process to form good ohmic contact; Step 4. Dissolve the cage-like monomer containing mercapto and the monomer containing olefin bond as the skeleton material and the photocatalyst in the mixed solvent of tetrahydrofuran and methanol; dissolve the pre-polymer containing mercapto and containing olefin bond and a small amount of photocatalyst in the mixed solvent of tetrahydrofuran and methanol; drop a small amount of precursor solution on the surface of the sensitive gate area of the HEMT device, and place it under ultraviolet light for in-situ crosslinking reaction; finally, rinse with the same solvent system to remove the catalyst and unreacted raw materials; Step 5. Drop the precursor solution on the surface of the sensitive gate area of the HEMT device, and place it under ultraviolet light for 15-30 minutes; Step 6. Rinse with the mixed solvent in step 4; Preparation of ionogel material: dissolve 50.0 mg of mercaptopropyl polyhedral oligomeric silsesquioxane, 255.0 mg of vinylhexylimidazole bromide and 4.0 mg of benzoin dimethyl ether in 2 mL of tetrahydrofuran and 6 mL of methanol mixed solvent; drop 2.5 ul of precursor solution on the surface of the sensitive gate area of the HEMT device, and place it under ultraviolet light for 20-30 minutes for in-situ crosslinking reaction; finally, rinse with the same solvent system to remove the catalyst and unreacted raw materials; The mercaptopropyl polyhedral oligomeric silsesquioxane and the vinylhexylimidazole bromide in the humidity-sensitive material are reacted in a ratio of 1:12; The solvent for the reaction in step 4 is methanol and tetrahydrofuran, and the ratio is 3:1; The click chemistry reaction in step 5 is carried out in-situ on the gate area of the HEMT device; The time of click chemistry reaction in step 5 is 15-30 minutes.

2. A HEMT humidity sensor for respiratory monitoring, characterized in that The HEMT humidity sensor for breath monitoring is prepared by the method of claim 1, and the HEMT humidity sensor is applied to the detection of humidity in human exhaled gas.

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