Modeling and simulation of polycrystalline ZnO thin-film transistors

Abstract

Thin film transistors (TFTs) made of transparent channel semiconductors such as ZnO are of great technological importance, because their insensitivity to visible light makes device structures simple. In fact, several demonstrations are made on ZnO TFT achieving reasonably good field effect mobilities of 1-10 cm2/Vs, but reveal insufficient device performances probably due to the presence of dense grain boundaries. We have modeled grain boundaries in ZnO thin film transistors (TFTs) and performed device simulation using a two-dimensional device simulator for understanding the grain boundary effects on the device performance. Actual polycrystalline ZnO TFT modeling is commenced with considering a single grain boundary in the middle of the TFT channel formulating with a Gaussian defect distribution localized in the grain boundary. A double Shottky barrier is formed in the grain boundary and its barrier height are analyzed as functions of defect density and gate bias. The simulation is extended to the TFTs with many grain boundaries to quantitatively analyze the potential profiles developed along the channel. One of the big contrasts of polycrystalline ZnO TFT compared with a polycrystalline Si TFT is that much smaller nanoscaled grain size induces heavy overlap of double Shottky barriers. Through the simulation, we can estimate the total trap state density localized in the grain boundaries for a polycrystalline ZnO by knowing apparent mobility and grain size in the device.Comment: Submitted to Journal of Applied Physic

High mobility amorphous zinc oxynitride semiconductor material for thin film transistors

“…It was reported that traps in the dense grain boundaries of crystalline ZnO can severely affect the overall performance of the TFTs. 8 In addition, the control of grain nucleation and uniformity of grain size at the critical gate insulator-semiconductor interface make crystalline ZnO a challenging and unfavorable choice for use in the economical bottom gate TFT structure used in current large-area display. More recently, amorphous indium-gallium-zinc oxide ͑IGZO͒ has been studied and developed, revealing a new path for producing high mobility amorphous semiconductor material through multicomponent post-transition-metal oxides.…”

Self-assembled nanocrystalline ZnO thin film transistor performance optimization for high speed applications

“…When the gate bias is higher than the threshold voltage, band bending at the interface allows the formation of a conductive channel. Potential barriers at grain boundaries are also lowered by the gate potential [27][28][29][30] and the current flow proceeds perpendicular to nanocolumns toward the drain contact.…”

Importance of Simulation Studies in Analysis of Thin Film Transistors Based on Organic and Metal Oxide Semiconductors

“…The total density of states g(E) is assumed to have exponential distribution of donor (D) like and acceptor (A) like defects that follow the equations 4a and 4c, respectively. This DOS model is attractive because of its simplicity and accuracy and has been used as the basis for many studies on metal oxide based TFTs (Hossain et al, 2003(Hossain et al, , 2004Fung et al, 2009;Ming et al, 2009) . Additionally, traps at the semiconductor -dielectric interface are assumed, which are defined by their concentration (N it ) and energy level (E it ).…”

“…In traditional electronics, device modelling and simulation has proven to be of great help in not only understanding the detailed device operation but has also served as a powerful tool to design and improve devices. The physics based device simulation is also becoming beneficial to the research area of organic and metal oxide semiconductors TFTs, where it is effectively predicting the device behaviour, giving insight into the underlying microscopic mechanisms and providing intuitive information about the performance of a new material (Bolognesi, 2002;Gupta et al, , 2009Gupta et al, , 2010Hill, 2007;Hossain, 2003;Scheinert, 2004). Its continued involvement for explaining various device phenomenons will certainly be of great use for future developments.…”