氧化鋅薄膜壓電觸覺感測器之研究

Abstract

本論文利用射頻磁控濺鍍法在低溫下沉積氧化鋅壓電薄膜於氧化銦錫/玻璃基板上，藉由改變濺鍍時氬氣/氧氣之氣體流量比例、濺鍍壓力、濺鍍溫度與後退火製程來製備氧化鋅壓電薄膜。藉由X光繞射儀分析後得知在氬氣/氧氣之氣體流量比例為42/0 <sccm/sccm>、濺鍍壓力5 mtorr、濺鍍溫度為室溫下濺鍍且無後退火製程時，可得高c軸從優取向之氧化鋅壓電薄膜。接著我們架設了一系統來進行不同機械推力與按壓頻率下之壓電輸出電壓量測，並研究不同濺鍍參數對500 nm厚之氧化鋅薄膜峰到谷輸出電壓的影響。結果顯示在氬氣/氧氣之氣體流量比例為42/0 <sccm/sccm>、濺鍍壓力5 mtorr、濺鍍溫度為室溫下濺鍍且無後退火製程時，所獲得之輸出電壓最高，此與X光繞射分析和掃描式電子顯微分析結果相符。 由於氧化鋅本身為半導體N型材料，故壓電效應產生之感應電洞可能受到氧化鋅內部自由電子的屏蔽效應(screening effect)，使得峰到谷輸出電壓量值下降。為了解決此現象，我們加入50 nm原子層沉積之二氧化鉿絕緣層抵擋漏電流，經量測後發現在施壓力道500 gf、頻率10 Hz的情況下，輸出電壓由2.688 V上升到3.254 V，提升了17.4 %。此外，研究中亦將感測器連接至互補式金屬氧化物半導體(CMOS)反向放大電路，藉此增強輸出電壓訊號，採用之CMOS反向器包括市售與研究團隊自行製備之氧化物CMOS反向器，而壓電感測器透過這兩種放大電路所得的輸出電壓皆能被反向放大，所得之放大波形並無明顯失真。

In this research, ZnO piezoelectric thin films were deposited by rf-magnetron sputtering on indium tin oxide (ITO) glass substrates at low temperatures. The effects of argon/oxygen (Ar/O2) flow ratio, deposition pressure, substrate temperature and post-anneal condition on the properties of ZnO thin films were investigated. The X-ray diffraction (XRD) analysis reveals that the ZnO thin film deposited at 42/0 <sccm/sccm>, 5 mtorr, room temperature and without post anneal exhibits good crystallinity with c-axis orientation. We then designed and setup an apparatus to measure the piezoelectric output voltages of 500-nm-thick ZnO thin films in response to cyclic forces with various amplitudes and frequencies. The largest peak-to-peak output voltage was obtained in the ZnO thin film deposited at 42/0 <sccm/sccm>, 5 mtorr, room temperature and without post anneal, which was consistent with the XRD result. Because ZnO is an N-type semiconductor, the holes induced by the piezoelectric effect may be screened by the excess free electrons in the ZnO thin film, causing the reduction of peak-to-peak output voltages. To mitigate this issue, we introduce a 50-nm-thick atomic layer deposited (ALD) HfO2 insulating layer to minimize the leakage current and improve the peak-to-peak output voltage. The output voltage of the HfO2/ZnO piezoelectric thin-film piezoelectric sensor in response to the pulsed mechanical force of 500 gf with a repetition frequency of 10 Hz is 2.688V. The output voltage of the HfO2/ZnO piezoelectric thin-film piezoelectric sensor under the same pulsed mechanical force condition is 3.254V, enhancement is 17.4%. In addition, we also connected the ZnO thin-film piezoelectric sensor to a CMOS inverter amplifier to enhance the output signals.