非晶氧化銦鎵鋅薄膜電晶體 之堅實性與新穎電路之研究

Abstract

本篇論文分成兩個部份來研究氧化銦鎵鋅薄膜電晶體(IGZO TFT),第一個部 分探討在以大世代面板既有的非晶矽薄膜電晶體的結構(底部閘極 (BG)結構)下, 各種元件結構的變形,在使用IGZO作為主動層時所遭遇的困難與其可能的解決 辦法。傳統探討電晶體是否適於大面積面板製作的討論,多半局限於元件初始電 性與可靠度的探討。本文以另一個角度來討大面積面板製作時,電晶體所該考慮 的問題。其中包含了靜電防護能力,銅導線的適用性以及元件縮小可行性。 第二部分則是以第一個部分所討論出來之元件結構中選擇最容易製造且寄生 電容與未來元件結構最相似的co-planar結構,利用所提出的雙閘極氧化銦鎵鋅薄 膜電晶體(DG IGZO TFT) 的元件特性來探討其可能之電路應用。 DG IGZO TFT的臨界電壓可透過頂部閘極 (TG) 來操控。基於這個現象,我 們提出了透過操作頂部閘極來補償臨界電壓變異的新概念。在本篇論文第二部分 的前兩個章節中,將此新概念應用到數位緩衝器(digital buffer),差動對(differential pair)和有機發光二極體(OLED) 的畫素電路中,並利用實驗驗証了這個新概念。 此外我們還將DG IGZO TFT用於主動式矩陣觸碰感測電路與RC低通濾波器。藉由 觸摸事件所導致RC時間常數的增加,一個明顯瞬態導通電流的出現,可作為感 測訊號。這個信號可以很容易地被讀出,從而減少外圍感應IC的成本。此外該傳感器,當它沒有被觸及時,由於沒有信號電流發生,因此消耗較少的待命功率。 這樣的設計使得以往的觸摸感應技術的缺點有相當大的改進。

This dissertation is divided into two parts. First part works on the device characteristics with the thin film transistor (TFT) structure called “bottom gate”, which is based on current large generation a-Si TFT back plane’s structure. With various device structures using IGZO as active layer, we study the difficulty and weakness of every structure and their possible solution. Different from conventional device stability analysis, this work focused on the other issues related with embedment device into large size display such as the protection of ESD, feasibility of Cu wire, and the possibility of shrinking device size. The second part of our study is choosing the co-planar structure, which is more compatible to the BCE structure on parasitic capacitance to do the dual gate (DG) IGZO TFT’s circuit study. Since the dual gate IGZO TFT can be controlled by both its top and bottom gates, we proposed inverter and differential amplifier are developed based on the new concepts of self-compensation and feedback with DG a-IGZO TFT. Also, the concept of using top gate of DG TFT to compensate TFT Vth is verified in examples of digital buffer and AMOLED pixel circuits through our experiment. Besides, we have verified the feasibility of the proposed DG TFT sensing circuits for touch. We use the pulse overlapping method to detect touch events. The proposed sensing circuit has many advantages. Firstly, it is active touch and sense. Therefore, the design consumes low standby power. In addition, the circuit supports multi-touch. Thus, the proposed sensing circuit provides an excellent way of implementing large area active matrix.