Influence Of Active Layer Regulation On Thin Film Transistor Electrical And Sensing Properties

Thin-film transistors?TFTs?are the key elements for flat-panel displays,memory cards,radio frequency identification tags and other electronic devices applications.Current microelectronics technology is almost exclusively based on the technology of single crystalline silicon.While the technology has been scaled over many orders of magnitude to reach highest performance,there are many novel applications where this technology is less suited because properties like large-area,flexibility,and easy processing.In order to replace the traditional silicon,solution-processed organic and metal oxide semiconductors and dielectrics films have attracted great research interest because of their large-area processability in ambient,potential for low cost,mechanical flexibility,and electrical/morphological uniformity over large areas.However,organic materials and oxide materials each have their own disadvantages.The main organic TFTs drawbacks are characterized by much lower mobilities and inferior stabilities.And solution-processed oxide TFTs are limited to the usually higher annealing temperature required.Meanwhile,transistor-based sensors show various advantages,including fast response,feasibility for miniaturization,easy processing,and high throughput.To overcome these shortcomings and applied in the sensor,in this ph.D.thesis,a variety of active layer regulation methods were utilized to improve the TFTs and transistor-based sensor performance,including dielectric regulation and semiconductor regulation in organic TFTs,and anion doping regulation in metal oxide TFTs.This study was divided into the following three parts:1.Influence of functionalized biocompatible dielectric,dielectric hybrid,and dielectric surface regulation on the performance of OTFT and gas sensors were studied.Cross-linked cinnamates of natural carbohydrates are very good TFT gate dielectric materials exhibiting excellent dielectric strengths and surface morphologies.Both p-type?Pentacene?and n-type?PDIF-CN₂?OTFTs have excellent transport characteristics.Silk fibroin?SF?:poly?vinyl alcohol??PVA?blends were prepared as the dielectric layers of OTFTs.Moreover,the OTFTs based on SF:PVA-blended dielectric exhibited a higher mobility and bias stability than those based on pure SF dielectric.An ultra-high sensitive ammonia?NH₃?gas sensor that incorporates a biocompatible/degradable gelatin dielectric layer in a top-contact OTFT.Moreover,an excellent limit of detection of 174.0ppb for this type of sensor,is demonstrated.2.Influence of semiconductor surface regulation and nanofibrillar structured semiconductor on the performance of OTFT and gas sensors were studied.Bottom-gate bottom-contact OTFTs and OTFTs based nitrogen dioxide?NO₂?sensors with 4,4',4''-Tris?N-3-methylphenyl-N-phenylamino?triphenylamine?m-MTDATA?or Mo O_x as the metal semiconductor interfacial regulating layer were fabricated.Compared to OTFT without interfacial layer,the field-effect mobility?m?was enhanced from 0.018 cm²/Vs to 0.15 cm²/Vs by incorporating with Mo O_x interfacial regulating layer.Moreover,the NO₂ sensitivity of OTFT with Mo O_x interfacial regulating layer is enormous higher than that of the controlled device.A series of sub-ppm sensitive and highly responsive OTFT NO₂ sensors based on nanofibrillar structured TIPS-pentacene by off-center spin coating were fabricated.When exposed to 30 ppm NO₂,the gas sensitivity of the orthogonal device was nearly 7 times better than that of the on-center device.On the other hand,the parallel device showed a remarkable sensitivity under 1ppm NO₂,which was approximately 35-fold greater than that of the on-center spin coating device.3.The influence of fluoride doping on the performance of metal oxide-based capacitor and TFT was studied.First,low-temperature solution-processed Al O_x films with excellent dielectric properties and frequency stability are achieved by fluoride doping.fluoride-doped?F:Al O_x?films exhibiting stable dielectric response over a wide frequency range??=4.3-3.4 at 0.1-10⁴ Hz?and excellent dielectric strength?7.0 MV/cm?.Then,both n-type?In₂O₃?and p-type?organic semiconductor?transistors with F:Al O_x gate dielectrics exhibit neglectable hysteresis and reliable transport characteristics,which are similar to those reported for control devices fabricated with high-quality thermal Si O_x gate dielectrics.In summary,to overcome the relative low mobility,poor stability and high cost in organic and metal oxide based TFTs,high performance TFTs and their sensors were fabricated by various active layer regulation methods,which pave the way for the extensive applications of TFTs in the field of opto-electronic and sensitive electronics.