砷化鋁鎵/砷化鎵異質接面結構雙極性電晶體之研究

Abstract

砷化鋁鎵/砷化鎵異質接面結構雙極性電晶體(HBTs)因其在高速纇比及數 位電路上的應用性，近來頗受矚目。在此，我們研究了一些先進的製程技 術。同時我們亦討論了這種元件的高頻極限。 我們在論文的開頭即描述突變型和漸變型異質接面結構雙極性電晶體的模 型。很明顯地,漂移-擴散模型並不適用。因此我們採用熱放射-擴散模型 。我們利用一階近似推導了高頻異質接面結構雙極性電晶體的小訊號參數 。利用這種參數我們可以估計不同的結構變數對電晶體高頻的影響。 在實驗上，我們發展一種不需要離子佈植，用以製作直流和高頻異質接面 結構雙極性電晶體的製程。這種製程包含了射-基極自動對準法，用以降 低基極外圍電阻；微細空氣橋，以隔離元件；鈀/鍺/鈦/金-n型歐母接面 ；以及重鉻酸鉀為主的選擇性溼式蝕刻。我們最後用掃描式電子顯微鏡來 檢閱製作完的元件。 我們利用 HP-8510來量測電晶體的高頻表現。開路與短路結構量測基墊同時被做在 晶片上用以扣除基墊的外在效應。另外我們也研究了delta-摻雜對異質接 面結構雙極性電晶體的直流和高頻的影響。 AlGaAs/GaAs heterojunction bipolar transistors ( HBTs ) have received much attention recently for applications in high- speed analogue and digitalcircuits. Several advanced process technologies have been developed in ourstudy. High frequency limitations on HBTs are also discussed. Model of bothabrupt and graded HBTs is described at the beginning of the thesis.It is shownthat a drift-diffusion model is not suitable in both cases. A thermionic-diffusion model is presented. The first- order approximations of high frequencyHBTs parameters are derived to examine various structural parameters thatinfluence HBTs. In experiments, we developed a method to fabricate AlGaAs/ GaAs d.c. andmicrowave heterojunction bipolar transistors without ion-implantation. Thismethod consists of a emitter- base selfalignment to reduce the extrinsic baseresistance, micro-airbridge to isolate devices, Pd/Ge/Ti/Au n-type ohmiccontacts, and K2Cr2O7 based selective etching solution. The results wereexamined by the scanning electron microscope. High frequency performance of HBT was measured by HP-8510 Network Analyzer.Open and short pad structures were also fabricated to subtract the extrinsiceffects. The inserted emitter base junction delta-doping HBT and undopedHBT were also fabricated and compared both in d.c. and r.f. range.