Design, Fabrication And Test Of “Extended Gate” AlGaN/GaN HEMT Sensor

Field Effect Transistor?FET?is a semiconductor device which uses the field effect of the input circuit to control the current of the output circuit.In recent years,FET-based biochemical sensors have attracted great attention due to their advantages of label-free,easy miniaturization,simple preparation process,simple operation and high sensitivity.They are widely used in environmental monitoring,disease detection,national defense security,food safety and other fields.As an important branch of FET sensor,based on AlGaN/GaN high electron mobility transistors?HEMT?biosensors have better physical and chemical stability,high sensitivity and good biocompatibility compared with traditional silicon-based FET,and have the bright future in the field of biochemical sensors.In this paper,the application and improvement of AlGaN/GaN HEMT sensor will be studied.The main contents include the following two aspects:The first part:AlGaN/GaN heterojunction material is epitaxially grown on silicon as the substrate of devices.The"extended gate"AlGaN/GaN HEMT sensor chip is fabricated by etching,electron beam evaporation and magnetron sputtering.The device gate was functionalized with mercaptoethylamine and salicylaldehyde,and the Schiff base chemical group with specificity for copper ion was formed on the device gate surface,and a copper ion sensor was prepared.When the Schiff base functionalized device contacts the copper ion in solution,the polarity of the device gate surface will change.The copper ion sensor can be realized the function by observing the change of the source-drain current.In the experiment,the copper ion sensor successfully detects copper ions in the range of 1 fM to 1 uM,with a sensitivity of 1.23 uA/log[Cu²⁺],a short response time?<15s?,good specificity for common anions and cations in solution,and good linearity of the sensor?R²=0.994?.The second part:The current"extended gate"AlGaN/GaN HEMT sensor is to extend the gate region of the device from the chip region.The chip region is fully encapsulated,and only chemical modification and liquid detection are carried out in the extended gate region,so that the stability of the device can be improved.However,the repeated modification of the extended gate will reduce the reliability of the device during use,increase the detection cost and shorten the service life of the sensor chip.In order to solve the above problems,this paper further improves the traditional extended gate structure and designs a isolate gate structure AlGaN/GaN HEMT sensor.In order to distinguish conveniently,this improved extended gate structure device is called"disposable gate"structure.Compared with the traditional"extended gate"structure,the main advantage of this structure is that the device is completely separated from the sensor chip area,and the two parts are connected through the lead,so that only the sensor gate needs to be replaced after each use,while the chip area can be reused.This improves the stability and reliability of the device,at the same time,it also prolongs the service life of the chip and reduces the detection cost.The fabricate process of the"disposable gate"sensor chip is similar to the"extended gate"sensor chip.The"disposable gate"sensor chip only needs to sputter a layer of Ti/Au material on an additional silicon substrate to fabricate the disposable gate,and then the lead connection completes the fabrication of the"disposable gate"structure device.In this paper,the detection of prostate specific antigen?PSA?was completed by using the"disposable gate"structure.In the experiment,the detection range of PSA is 100 fM to 1 uM,the sensitivity is|???I/I₀|=0.0195×lg(C_PSA)+0.0053,and the linear correlation coefficient is R²=0.997.The anti-interference ability of the AlGaN/GaN HEMT sensor with the golden gate structure and the"disposable gate"structure under the light and mechanical disturbance is compared.The experimental results show that the"disposable gate"structure has better anti-interference ability,which lowers the encapsulation requirements of the sensor chip in practical application.