Oxide-based Electric-double-layer Transistors And Their Applications In Artificial Synapses And Biochemical Sensing

Recently,low-voltage transistors gated by electrolytes have attracted intense attentions due to their strong ionic/electronic coupling effect.Such electrolyte-gated electric-double-layer transistors?EDLTs?have potential applications in low-power portable electronics,artificial electronic synapses and ultra-sensitive biosensors.However,most studies focused on organic-based transistors gated by liquid electrolytes or ionic-gel.As a comparison,oxide-based transistors gated by solid electrolytes exhibit higher carrier mobility,better stability and encapsulation facilitation.On this basis,this dissertation investigated the electronic properties of solid electrolytes including sodium alginate films,free-standing chitosan membranes and nanogranular SiO₂ films.Moreover,we also investigated applications of oxide-based electric-double-layer transistors in artificial synapses and dopamine sensing.The main content can be summarized as follows:?1?A large EDL capacitance of ⁴.6 ?F/cm² and a high proton conductivity of ⁷.7×10-4 S/cm are measured in solution-processed sodium alginate?SA?electrolyte film,respectively.Owing to the protonic transporting in SA electrolyte film in three dimensions,the protons will migrate and form a lateral ionic/electronic coupling effect under lateral electric filed.Low-voltage in-plane-gate oxide-based transistors laterally gated by sodium alginate electrolytes are fabricated on glass substrates.The field-effect mobility,current ON/OFF ratio,threshold voltage and subthreshold swing of such transistors are estimated to be 9.5 cm²V-1s-1,3.1×106,-0.1 V and 100 mV/decade,respectively.The laterally coupled oxide transistor can work at low voltage?<1.5 V?due to the strong lateral coupling effects of the SA films.A resistor-loaded inverter is also proposed,featuring a voltage gain of ⁵.0 with low operating voltage of 1.0 V.Furthermore,AND logic operation is demonstrated when two in-plane gate electrodes are used as the input terminals.Finally,laterally coupled dual-gate oxide-based transistors on SA electrolytes have been demonstrated on flexible paper substrates,showing satisfied electric performances.AND logic operation is also realized on such paper transistors.?2?Free-standing chitosan membranes with high proton conductivity and large specific capacitance are prepared by a simple coating–peeling process.Our results show that the free-standing chitosan membrane is an electron-insulating but proton-conducting electrolyte membrane.Free-standing artificial synapses based on laterally coupled oxide-based transistors were fabricated on chitosan membranes,where chitosan membrane acts as the gate dielectric and the flexible mechanical support.The field-effect mobility,current ON/OFF ratio,threshold voltage and subthreshold swing of such synaptic transistors are estimated to be 14.2 cm²V-1s-1,1×106,-0.2 V and 120 mV/decade,respectively.In addition,the synaptic transistors also show satisfied mechanical bending performances.In-plane gate is used as the presynaptic input terminal and the indium-zinc-oxide?IZO?channel with source/drain electrodes is used as the postsynaptic output terminal.The IZO channel conductance is regarded as the synaptic weight,mimicking the spike working mode of the biological synapses.Synaptic functions,i.e.EPSC,STP,LTP,high pass filtering and spatiotemporally correlated signal processing have been mimicked in the free-standing synaptic transistors.The artificial synapses short-term plasticity behaviors are related to the EDL lateral modulation,and the long-term plasticity behaviors are due to the proton-related electrochemical doping of IZO channel layer.Moreover,artificial synaptic devices with multiple pre-synaptic inputs were investigated,and spiking logic operation and logic modulation were realized.“OR” and “AND” logic operation can be easily modulated by the spike applied on the third modulatory terminal.Such free-standing synaptic transistors may have a wide range of applications,such as bendable smart tags and synaptic electronics.?3?Low-voltage full oxide-based EDL transistors gated by nanogranular SiO₂ electrolyte films are fabricated on glass substrates for dopamine detection.Nanogranular SiO₂ electrolyte films with large specific capacitance?².0 ?F/cm²?are deposited on indium-tin-oxide?ITO?glass substrates by plasma enhanced chemical vapor deposition?PECVD?.By using surface functionalization and biomolecule immobilization on the ITO bottom gate,such oxide-based homojunction transistor sensor showed a high DA sensitivity and a good selectivity.A low DA detection limit down to 0.1 nM level was obtained at low operation voltage of 0.8 V.The sensing mechanisms are attributed to the modulation of surface potential of the ITO bottom gate electrode induced by the preferential binding of DA molecule to phenylboronic acid.The proposed low-voltage oxide EDL transistors have potential application in biochemical sensors.