Low-voltage Organic Small Molecules Field-effect Transistors And Their Applications

Organic field-effect transistor(OFET),due to its low cost,flexible and bendable,good biocompatibility,etc.has gained wide attention worldwide and has shown great potential for applications in the fields of sensors,healthcare,and flexible displays.However,most of the existing reported OFET device operating voltage is often tens of volts,which not only seriously affects the scope of application of OFET,but also cause serious power waste.Therefore,reducing the operating voltage of OFETs is one of the important trends in development.The preparation of low-voltage OFETs has been reported,but most of them are based on vacuum deposition process,which is not only complicated for circuit integration but also its preparation cost is not a negligible factor.In order to promote the better application of OFET,reflecting the balance of process,cost and performance,the following three works are carried out in this paper:1.Study of Low-voltage Organic Field-effect Transistors Approaching the Theoretical Limit of Thermal Ion EmissionIn this paper,a bottom-gate-bottom contact(BGBC)organic field-effect transistor is prepared by solution printing method to achieve the reduction of transistor operating voltage by creating an ideal metal electrode-semiconductor contact interface and minimizing the device interface trap state.The method is based on ink-jet printing,taking low-cost solution processing,selecting films of pinhole-free,water-oxygen-isolated terephthalene-c powder(Parylene-C)as the insulating layer,and finally squeegee directional scraping to obtain millimeter-scale single-crystal films of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene(C8-BTBT).It is shown that the single crystal film and insulating layer interface trap state density is only 7.8 × 108 eV-1 cm-2,the device has a low saturation operating voltage of-2 V,the threshold voltage is 0.15 V close to 0 V,and its lowest subthreshold swing is 62 mV dec-1,which is close to the theoretical limit(59.6 mV dec-1).,Similarly,its signal amplification efficiency is 37.1 S A-1,which is close to the theoretical thermal ion emission limit.In addition,the electrode-to-semiconductor contact barrier of the constructed OFET device is 0.55 eV,which is very close to the theoretical Schottky barrier(0.5 eV)calculated by the Schottky-Mott rule,indicating that the prepared OFET device is a low-voltage Schottky organic field effect transistor with an ideal physical model.On the one hand,this work demonstrates that an ideal interface for bottom-contact devices can substantially eliminate the defect density of states and reduce the device operating voltage.On the other hand,this work provides a new way to prepare high performance low-voltage organic field effect transistors by low-cost solution method.2.Ultra-steep Sub-threshold Swing Low-voltage Organic Field-effect Transistor Monolithic Integrated Optical Response Amplifier Circuit and its Application in Health MonitoringIn the field of health monitoring,mutual limitations between photoresponse of photodetectors,structural complexity,and manufacturing cost have hindered further development of the emerging wearable photovolumetric tracings(PPG)technology.This work utilizes the constructed ultra-steep sub-threshold swing of low-voltage OFETs to significantly improve the performance of organic photodetectors and improve the performance of health monitoring systems.It is demonstrated that monolithic integration of OFETs with organic photoconductive devices can significantly amplify the optical response signal-to-noise ratio from 5.5 to 4.6×105 by more than 4 orders of magnitude and enable excellent responsiveness(R=16.57 A/W)and specific detection rate(D*=3.12 × 1013 Jones)in a low-light environment at 10 nW cm-2,enabling the monitoring system to meet the requirements of extracting physiological information from PPG waveforms to accurately extract physiological information.This work not only demonstrates that OFET can greatly improve the performance of photodetectors,but also constructs a monolithic integrated optical response amplifier circuit for daily health monitoring applications to achieve effective extraction monitoring of heart rate,blood oxygen and blood pressure,which is expected to revolutionize health monitoring technology.3.Low-voltage Organic Field-effect Transistors Electrically Stimulate Nerve CellsIn healthcare,understanding the bioelectrical behavior of nerve cells or probing the mechanisms of nerve cell work patterns is stimulating the development of cell sensing platforms,where power consumption and biocompatibility are uncompromising requirements.On the one hand,the OFET in this work has an output power consumption of only 0.02 pW-0.02 nW in the subthreshold interval and shows long time stability in all three cell solution environments.On the other hand,the OFET does not cause contamination and toxicity to neuronal cells,and using control experiments,it was found that neuronal cells cultured on the OFET and blank groups,respectively,had good cell morphology with cell densities.This indicates that OFET exhibits good biocompatibility.This work has not only successfully achieved the modulation of current and voltage inside and outside the nerve cell membrane by OFET electrical stimulation,but also demonstrated the great potential of OFET in the field of biological cell sensing platform.