Strained-Si Technology and SiGe Optoelectronics Devices
Date Issued
2006
Date
2006
Author(s)
Yuan, Feng
DOI
en-US
Abstract
In this dissertation, the SiGe optoelectronics device and circuit applications with SiGe heterojunction phototransistor (HPT) are studied. The digital and analog circuit with MOSFET and the characteristics of bipolar device under external mechanical strain are also comprehensively investigated.
First, the integration of the photodetector is essential for optical communication chips. However, to utilize the SiGe HPT as a photodetector, the accurate device model should be chosen. The Gummel-Pool model is not capable to model the SiGe HPT due to the simplicity of the model and inaccuracy on high current operation and poor frequency response predicability. Three candidates for the compact bipolar device model such as VBIC, Hicum, and Mextram, are studied and compared. The Mextram model has the accuracy on high current operation and frequency response characteristics with less model parameters than other two models. Therefore, we choose Mextram model in our further device modeling on SiGe HPT under optical illumination.
The SiGe HPT is integrable with SiGe heterojunction bipolar transistor (HBT) process and can be modeled by a modified Mextram model for the circuit simulation. The impact ionization to obtain an extra gain for the optoelectronic conversion and the “Early voltage reduction” under constant illumination are well-modeled in a modified model. The nkT recombination current and the substrate contact to enhance the HPT speed are incorporated in ac model. It shows a good agreement between measurement and simulation.
The transimpedance amplifier (TIA) circuit with 10GHz bandwidth is designed and fabricated. The ~500Ω transimpedance gain and the ~10GHz bandwidth are achieved. The eye-diagram with 10GHz 215-1 non-return-to-zero (NRZ) pseudo random binary sequence (PRBS) data input shows a good eye opening result, indicating an appropriate application in OC192 standard for 10GHz optical communication system. Furthermore, the integrated SiGe HPT with TIA circuit is fabricated. The impulse response shows a ~0.5GHz bandwidth under 850 nm optical illumination. The slow speed of the integrated SiGe HPT with TIA circuit is limited by the HPT without additional multiple quantum well absorption.
Then, the strained-Si technology is reviewed and studied. The appropriate external stress can enhance device and circuit performance. The external mechanical strain has the flexibility to provide strain on various directions and can be applied after device fabrication. The 7.4% speed enhancement is achieved for the 250 nm node ring oscillator under uniaxial tensile strain for mutually perpendicular layout of the NFET and the PFET. The speed enhancement is less than 1.5% for the conventional parallel layout of the NFET and the PFET. A 180 nm node transimpedance amplifier has ~5% bandwidth enhancement using biaxial tensile strain or uniaxial tensile strain parallel to NFET channel to tune the peaking frequency of active inductor in the circuit. The package strain can provide an extra useful parameter for the future digital and analog circuit design.
Finally, the current gain ( β = IC/IB ) variations of the mechanically strained SiGe HBT and Si bipolar junction transistor (BJT) devices are investigated experimentally and theoretically. The β change of HBT is found to be 4.2% and –7.8% under the biaxial compressive and tensile mechanical strain of 0.028%, respectively. For comparison, there are 4.9% and –5.0% β variations for BJT under the biaxial compressive and tensile mechanical strain of 0.028%, respectively. The current change due to externally mechanical stress is the combinational effects of the dependence of the mobility and the intrinsic carrier concentration on strain. In SiGe HBT, the mechanical stress is also competing with the compressive strain of SiGe base, inherited from the lattice misfit between SiGe and Si.
Subjects
矽鍺技術
異質接面光電晶體
光偵測器
模型化
轉阻放大器
應變矽技術
特殊佈局方向
機械應變力
環型振盪器
雙載子電晶體
異質接面雙載子電晶體
SiGe
heterojunction phototransistor (HPT)
Mextram
photodetector
device modeling
transimpedance amplifier (TIA)
strained-Si technology
layout direction
mechanical strain
ring oscillator
bipolar junction transistor (BJT)
heterojunction bipolar transistor (HBT)
Type
thesis
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