CMOS橫向雜散雙極性電晶體在能隙參考電位線路中之特性分析, 模擬以及設計製作

Abstract

近來CMOS製程中之橫向雜散雙極性電晶體已被應用在一些數位與線性整合 性的線路中, 它之所以被接受與應用, 乃在於其較低的製造成本以及較成 熟之製造技術, 本篇論文中, 我們嘗試以CMOS中之橫向雜散雙極性電晶體 應用在能隙參考電位線路中, 所有的實驗均是在0.8um CMOS製程下所完成 的, 在完整的實驗線路中, 包含了鏡像電流反映器, 操作型放大器, 以及 外部緩衝級等. 對於這樣的一線路將可以被廣泛的應用在數位對線性的轉 換器中, 然而此一線路最值得注意的地方, 乃在於其對溫度的穩定性上. 在橫向雙極性電晶體的設計上, 我們亦做了相當的努力, 以便使此一電晶 體能得到較大的輸出電流. 實驗中我們所能達到的 hfe接近30左右.為了 能精確的以 SPICE模擬線路的輸出, 橫向雙極性電晶體的模型以及其各項 的參數均是必須的, 此項工作我們以現成的套裝軟體AURORA來完成參數萃 取的工作, 由萃取出之參數所構成的電晶體模型與實際元件比較中, 我們 發現在主動區域, 模型與實際元件可有完美一致的表現 , 但在飽和區域 卻有較大的出入, 此一原因將歸因於此一橫向電晶體元件在CMOS製程中是 與一縱向電晶體並存而生的, 這將影響此一元件在飽和區域中之表現, 在 線路輸出模擬上, 我們將線路設計在70℃時對溫度有最小的變異性, 而實 際線路中所測量的結果, 則是在90℃時對溫度有最小的變異性. Parasitic BJT's in a standard CMOS technology have been implemented in some mixed-mode digital and analog circuits. The advantages are to reduce fabrication cost and technology complexity. In this thesis, we intended to implement BJT's in the lateral direction in a bandgap voltage reference circuit using a standard 0.8um CMOS technology. The circuit includes a current mirror, an operational amplifier and an output buffer for a constant output current. Temperature stability is a key concern of this circuit for the purpose of accurate conversion between digital and analog signals. The layout geometry of the BJT's have been optimized to find a highest current gain in the current mirror circuit. A current gain of nearly 30 has been achieved. In order for SPICE simulation, lateral BJT SPICE modeling is needed. Device characterization and parameter extraction are done with a commercial software AURORA. Good agreement between modeling and measurement is emphasized in the active region, where the devices are operated in a current mirror circuit. In the saturation of the BJT's, a large discrepancy from the SPICE model is observed due to the contemporary existence of parasitic vertical BJT's. SPICE simulation of the bandgap reference circuit has been performed at various temperatures. The optimization of the circuit is attempted for a minimum temperature sensitivity around an operational temperature about 70℃. In experiment, the circuit was fabricated and characterized. The measured results show minimum temperature dependence of the output current around T=90 ℃.