由應力產生超低雜訊金氧半電晶體在可撓曲塑膠基板上之影響與模擬

Abstract

由於磨薄矽基板在塑膠基板上所具有的高度可撓取性，故可施加更大的應變於電晶體上使元件特性更近一步的改善。將矽晶片磨薄至30微米並固定在塑膠基板上施以一伸張應力，在頻率為10 GHz時我們量測到很低的NFmin 值為0.96dB與有高的相關增益值為14.1dB。藉由使用新思公司的製程元件模擬軟體(Taurus-Suprem4, Taurus-Medici and Taurus-Device)，我們也模擬出由應力導致元件特性改變的影響。為了能符合實際元件的趨勢，首先模擬元件的製程步驟與量測元件(0.18微米電晶體)的製程步驟相同。在模擬元件特性部分，選擇合適的物理模型並合理調整參數以符合實際量測數據得到準確的模擬結果。在做完模擬元件的校正後，導入與實際施加伸張應力相似的應力分布場，以模擬在伸張應變下的電晶體。從模擬與量測的數據所呈現高的驅動電流是由於施加應力所引起電子遷移率增加。另外，隨著所施加的伸張應力增加，轉導增益、射頻電流增益與截止電壓也隨之增加使得高頻雜訊獲得改善。藉由模擬軟體的幫助，我們也研究施加的應變場變動對元件高頻特性的影響與現象像是應力所引起的能隙改變與臨界電壓的降低等。在後續的研究方面，將研究並模擬不同施加應力的方式所造成的應變場是否能有效的增進電晶體的高頻特性。

Due to high flexibility of silicon thinner substrate thickness on plastic, larger tensile strain can be applied for further improvement. A low minimum noise figure (NFmin) of 0.96dB and high associated gain of 14.1dB at 10GHz, were measured for 0.18□m MOSFETs on plastic, made by substrate thinning (~30□m), under applied tensile strain. Effects of strain-induced characteristics have been simulated by using Synopsys’s TCAD (Taurus-Suprem4, Taurus-Medici and Taurus-Device). In order to attain the trend of actual transistor, the device is simulated firstly by using the recipe is following the 0.18□m MOSFET process. Then, we choose proper models and adjust the parameters to get good match between measured and simulated data. After calibration of simulated data, the strain field which is similar to actually tensile strain is included to simulate strain silicon transistor. From the results of simulated and measured data, the higher drive current is presented and is due to strain-induced high mobility. RF noise improvement is resulted from increased gm, RF gain, and cut-off frequency (ft). By help of the simulator, we investigate how the variation of strain field affects the RF performance, the trend of down-scaling the transistor with noise figure and other phenomenon such as strain-induced bandgap change. Other different types of strain profile, which can effectively improve RF characteristics, can be simulated and investigated in future.