Research On Compact Model And Parameters Extraction For Metal Oxide Thin-film Transistors

Compared with amorphous Silicon?a-Si?,poly-Silicon?poly-Si?and organic thin film transistors,the metal oxide thin film transistor?MOTFT?has high carrier mobility,good uniformity and bending performance,and low cost deposition.Hence,MOTFT has found wide applications in the flexible circuit and active matrix organic light emitting diode?AMOLED?panel,etc.It plays an increasingly important role in this application prospect.In the future applications,MOTFT will also be applied to flexible Radio Frequency Identification?RFID?circuits,digital and mixed-signal circuits,and biologically restorable biosensors and circuits,and so on.In order to better promote the development of MOTFT,it is essential to establish a compact model with physics.The compact model can make us in-depth understanding the electrical characteristics of devices and the impact of new materials on TFT performance.Finally,it helps to assist the design of MOTFT based integrated circuit.The main contents of this paper include the proposed extraction of interface and bulk density of state?DOS?,which is based on the device characteristics and takes the influence of interface trap charge into account.At the same time,an extraction method of contact resistance is proposed based on the contact voltage method.Using the results of parameter extraction,a surface-potential-based current?DC?compact model is proposed considering the contact effectThe density of states in the active layer of MOTFT dominates the electrical characteristics and stability of device.It is indispensable to propose a physical-based and straight-forward extraction technique for interface and bulk density of states.It can help us not only to understand the device characteristics,but also to establish a more accurate DC model.The metal oxide band-gap trap states are mainly composed of the oxygen vacancies,the shallow donor states of oxygen vacancies,and the tail states of valence bands and conduction bands.An extraction methodology for interface and bulk density of states that takes the interface charge into account is proposed in this paper.The MOS capacitor is the series combination of the oxide capacitor C_ox and the parallel combination of the silicon capacitor C_s and interface charge capacitance C_it.The DOS can be extracted by using this method that needs only one curve of the C-V characteristics,which is a simple and more accurate method.The DOS is substituted into the device simulation software to get the I-V characteristics.The I-V characteristics and experimental data are in good agreements.As the device size continues to shrink,the effect of the contact resistance will be more and more important on the devices.The impact of the contact resistance is more relevant to short channel length devices,where the contact resistance may become comparable to,or even larger than,the channel resistance.Therefore,an accurate extraction of contact resistance plays an important role in modeling.In order to extract the contact resistance,the contact voltage method is proposed in this paper,which divides the channel into two parts:the contact channel and the intrinsic channel.If contact voltage can be accurately extracted,the contact resistance can be obtained.The method assumes that the electrons injected into the active layer at the source side are completed in the line-injection.Based on the results of parameter extraction and the calculation of surface potential,a DC model considering the effect of contact resistance is proposed,including subthreshold and accumulation regimes.Owing to consider the contact effect and degenerate conduction regime,the DC model can be applied to devices with different channel lengths and suited to the devices operating in degenerate regime.Hence,the complete and physical-based DC model can be embedded in a circuit simulator.Using the DC model,the I-V characteristics with different channel lengths can be obtained.By comparing with experimental data,it is found that the model and experimental data are in good agreement.In conclusion,the extraction method of DOS and contact resistance is proposed.Based on the results of extraction and surface potential,a DC model considering the contact effect is established.The validity of parameter extraction and DC model was verified by comparisons with the experimental data.