Study On The Logic Function Of Coplanar Dual-Gate Ion-Gated Transistors

Logic gate circuit is the key circuit unit of digital integrated circuit,which is also the basic structure of digital system.It is usually composed of CMOS or TTL logic circuit.In recent years,as a new type of semiconductor device,ion-gated transistors have attracted much attention for its characteristics of low voltage,multi-gate regulation and applications in chemical sensing and brain-like devices.Because the ion-gated transistors have the ability of side long range regulation,it is very conducive to the preparation of coplanar dual-gate structure.Furthermore,the ion in the gate medium and the electron coupling in the channel are controlled by dual-gate with different voltage inputs applied,so as to achieve the unique logic function output.In addition,the relativety slow ion transport in the gate medium was considered as the limiting factor that causes the slow response speed and low operating frequency of the ion-gated transistor,which can’t be used in the logic gate circuits.It is also a difficulty in the research of ion-gated transistors.Therefore,this topic taked a coplanar dual-gate structure of ion-gated transistors as the research object,two gates of the device for control,successfully realized a variety of structure simplified logic gate circuit.Further more,we cleard the key factors restricting the dynamic response speed of ion gate transistor,studied the experimental model of its gate control mechanism.It is expected that the dynamic response speed can be improved by optimizing the device structure and material properties in practice.Based on the above cognition,combined with the device preparation technology,electrical performance testing,logical function realization,electrochemical impedance analysis,ion transport mechanism and hydrogel materials,this paper carried out the following research:（1）Prepare planar-side-gate ion-gated transistor devices and test their basic electrical properties.Firstly,the mask plate of the coplanar dual-gate device was designed,and PSSNa solution was prepared as the gate medium.By magnetron sputtering technology,the IGZO channel and IZO source/drain electrode and gate electrode were prepared.Then,the transfer characteristics,output characteristics and switching characteristics of the coplanar two gates were tested respectively by the external source meter of the probe station.The I_on/I_off ratio of the device reached about 10⁴,the V_th was about-0.24V and-0.25V respectively,and the mobility of the device was about 1.81 cm²·V^-1s^-1.The results show that,the device has good electrical properties and the two side-gates have basically similar electrical properties.In addition,the thickness of the central film of the PSSNa layer of the planar dual-gate ion-gate transistor was about 2μm,as measured by 3D laser scanning microscopy.（2）Realize a variety of logic gate circuits with simplified structure based on coplanar dual-gate structure ion-gated transistors.Firstly,the dual-gate control mechanism was theoretically analyzed and described.Then the current output form AND logic was successfully realized by using the probe station external signal generator,oscilloscope,multifunctional meter,DC power supply,etc.,and the voltage output of AND logic was realized by the follower circuit.Then the inverter circuit was built to realize the output of NOT and NAND logic voltage,and then the voltage output of OR and NOR logic was successfully realized.Finally,the dynamic response time of various logic devices was calculated,which is consistent with the response time of ion-gated transistors reported in literature.（3）The ion transfer of ion-gated transistors was studied by impedance analysis method.Firstly,an appropriate equivalent circuit model was established,and the impedance of several devices with different structures was measured by using LCR meter.Then,the experimental data were fitted according to the equivalent circuit model,and the electrolyte resistance(R_EL)and ionic conductivity（σ）were obtained.The effects of several structural parameters on the ion transmission resistance were analyzed,and the effects of the above factors on the response speed of the device were clarified through the analysis of the equivalent circuit.The following conclusions were drawn:the smaller the distance between channel and gate electrode,the smaller the thickness of gate dielectric layer and the higher the concentration of ions in gate dielectric,the better the response speed of the device.At the same time,the impedance measurement results and dynamic response time of planar-side-gate and top-gate ion-gated transistors were compared and analyzed.It is proved that top-gate devices have more advantages in this aspect.（4）The hydrogel material as the electrolyte of ion-gated transistors was studied.Hydrogels are characterized by strong water absorption ability,good biocompatibility,fast ion diffusion speed,biodegradability,etc.Firstly,the synthetic materials and curing methods of hydrogels,as well as the hydrogels prepared in the laboratory were introduced.Then,the Ag/hydrogel/ITO sandwich structure was prepared,and the capacitor-frequency characteristics were measured.Then,the electrochemical impedance spectra were measured by changing the internal ion concentration of the hydrogel.The results showed that compared with PSSNa,the hydrogel had higher working frequency and larger capacitance per unit area,significantly reduced R_EL and increasedσ,and it had greater advantages as an electrolyte material.Finally,the planar-side-gate ion-gated transistors were prepared by the hydrogel by means of bonding.The electrical properties and the transient response time of the planar-side-gate ion-gated transistors were measured and calculated.It was proved that the hydrogel electrolyte can be well used in ion-gated transistor devices.