Study On Biochemical Sensor Based On GaN Field Effect Transistor

With the development of science and technology,electrochemical biosensor has become a reliable sensing device.It is a kind of devices that can detect chemical and biological molecules by using specific groups,separated enzymes,antigens,or nucleic acid through specific biochemical reactions.It can convert the concentration and activity signals into electrical signals（include current,voltage,capacitance,conductance,etc.）.This type of sensor has the advantages of short analysis time,simple operation,low cost,small sample volume,etc.,and has excellent performance such as reusability and high sensitivity.It only requires simple pre-processing in the face of complex samples.As the third-generation semiconductor material,GaN has been fully developed in power electronics technology.Its high electron mobility and stable chemical properties make it has a great advantage in biochemical sensing.When the AlGaN/GaN surface is in contact with the solution,the atoms or ions at the interface will form an electric double layer due to the interaction.At this time,the gate window can be used as a sensing electrode.Biomolecular sensing is achieved by specific modification of the gate.The two-dimensional electron gas induced by the spontaneous polarization of AlGaN/GaN has the advantages of high mobility and high concentration.So a small change in the gate surface propagate to the channel causing significant changes in the output current.Also this sensor has a huge advantage in terms of integration.Although many researchs have been carried out on AlGaN/GaN sensors,a lot of effort is still needed to fundamentally improve the sensitivity of the device by changing the device structure.This type of sensor still has the problem of surface-specific modification.Therefore,for the application of GaN in biochemical sensing,the main research contents of this paper include:1.AlGaN/GaN ion-sensitive field-effect transistors are fabricated as pH sensors.Hydrogen ions can be sensed due to the presence of native oxides and nitrides on AlGaN surface.The surface potential sensitivity（S_V）of the AlGaN/GaN ISFET is 55.81 m V/pH,which is close to the Nernst theoretical value of 59.5 m V/pH at room temperature.We use the recess structure to improve the current sensitivity（S_A）of the sensor,and at the same time use ammonia treatment to repair the etching damage.Through the gate recess process,the maximum transconductance（G_M）of the ISFET is increased from 0.8 to 2 m S,and the S_A of these pH sensors is improved from 52.25 to 78.86μA/pH.Furthermore,after treatment with ammonium hydroxide（NH₄OH）solution,the current sensitivity of the pH sensor was improved from 78.86μA/pH to 84.39μA/pH.According to the XPS results,combined with the energy band situation,it is shown that many nitrogen vacancies（V_N）are introduced during the etching process.This process brought a large number of interface states.It causes a negative threshold voltage shift and a decrease in S_V,while the ammonia treatment can repair it effectively.2.A new HfZrO₂/AlGaN/GaN ion-type field effect transistor pH sensor is proposed.In order to avoid the influence of the process of etching damage on the surface of the recess structure,we have grown ferroelectric material layers with different thicknesses to improve the transconductance of the sensor.When the HfZrO₂ film thickness is 15 nm,the maximum transconductance is improved from 0.8 m S to 1.4 m S.And the current sensitivity of the pH sensor is improved by 77%from 43.23μA/pH to 76.61μA/pH.3.A biosensor based on AlGaN/GaN heterojunction field effect transistors is proposed for the direct detection of tumor biomarker mi RNA-155.By immobilizing specific thiol-modified RNA（SH-RNA）probes on the Au-gate surface of AlGaN/GaN HEMTs,an RNA-Au-AlGaN/GaN HEMT biosensor is fabricated.The change of the two-dimensional electron gas concentration in the channel caused by the hybridization process of the surface RNA leads to a significant change in the output current,so that the biosensor can realize the rapid detection of mi RNA-155.Experimental results show that the linear range of the sensor is 2f M to 2 n M,and the detection limit is 1.81 f M.The sensor has a high current sensitivity of77μA/log and a surface potential sensitivity of 73 m V/log in the linear range.At the same time,the biosensor has good specific recognition ability and can distinguish target RNA in the case of only single base mismatch.At the end of the experiment,fluorescence microscope was used to confirm the immobilization of the RNA probe and the existence of the hybridization process.The AlGaN/GaN HEMT RNA sensors have high sensitivity with a wide linear detection range compared to other element-based sensors.4.A new type of split sensor based on AlGaN/GaN heterojunction transistors and molecularly imprinted films is proposed.The self-assembly phenomenon of the molecularly imprinted films can realize high specificity recognition of glucose molecules.The films prepared by cyclic voltammetry have good film-forming properties.The method is easy to control the thickness.Combined with the AlGaN/GaN HEMT,the test range is 0.29 m A.Linear detection in the range of 4-50 mg/L is achieved with a current sensitivity of 3.95μA/mg·L.After many repeated tests,the average current drift is about 0.6%.The device showed good repeatability and stability.In specificity tests,the device showed little response to other sugars.In particular,the response to the isomeric D-fructose was also very weak,which is due to the successful screening of interfering molecules by special pore sites in the formation of the molecularly imprinted film.Finally,the elution and adsorption processes in the sensing process were verified by Raman spectroscopy.The result provides a convenient and fast method for non-invasive glucose detection using saliva.