可撓性互補式氧化物電晶體反向器應用於壓電觸覺感測介面放大電路之研究

Flexible Complementary Inverters with Oxide Thin-Film Transistors and Applications to Amplifier Circuits for Piezoelectric Tactile Sensing Surface

李昀軒(Yun-Shiuan Li)

指導教授 ： 陳奕君

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2017年)

https://doi.org/10.6342/NTU201704450

摘要

本研究於可撓性聚醯亞胺塑膠基板上開發全氧化物薄膜電晶體互補式反向器及電路。首先以氧化鋅搭配氧化亞錫薄膜電晶體製作互補式反向器及震盪器電路，電晶體採用下閘極反向堆疊結構，並以低溫磁控濺鍍法製備通道層。所製備的可撓性互補反向器其P型電晶體與N形電晶體的元件通道幾何比為5，在供給電壓為12伏特時具有電壓增益12。接著探討在受彎曲應力下的元件電性表現，在施以張應力時觀察到薄膜電晶體與互補式反向器的電性表現劣化，而壓應力對於其電性表現沒有明顯的影響。
我們進一步運用單一通道層沉積技術來製備氧化錫與氧化亞錫薄膜電晶體互補式反向器。於N形電晶體區域選擇性覆蓋一層氧化鋯薄膜來提供氧原子，以在低製程溫度下實現N形電特性。研究中發現，背通道覆蓋氧化鋯薄膜的電晶體隨退火時間的增加其電性表現由P形轉為N形。所獲得的錫氧化物互補反向器於玻璃基板及聚醯亞胺塑膠基板上在供給電壓10伏特時，電壓增益值為13，在施以張應力時可觀察到薄膜互補式反向器的電性表現劣化。
由於氧化錫與氧化亞錫薄膜電晶體互補式反向器的電壓轉換點較小，我們運用氧化鋅與氧化亞錫薄膜電晶體互補式反向器搭配回授電阻來製備薄膜放大器作為壓電感測器的訊號放大。聚偏二氟乙烯(PVDF)壓電感測薄膜以及氧化鋅壓電感測薄膜分別以導線外接到放大器來提升訊號的強度。薄膜放大器於玻璃基板上可有效提升10倍輸出訊號量值。薄膜放大器於可撓性聚醯亞胺塑膠基板上可有效提升6倍輸出訊號量值。但經過放大後的訊雜比無提升，原因可能來自外接線路的雜訊以及外接過程中訊號的衰減。
最後，我們開發觸覺感測面來確認壓電薄膜與薄膜放大器一體整合之可行性。觸覺感測面包含四個獨立的感測區域，每個區域由一壓電薄膜與一個薄膜放大器所組成。當採用聚偏二氟乙烯(PVDF)壓電薄膜時，可成功放大電壓訊號達11倍，此時訊雜比為32分貝。而以氧化鋅壓電薄膜與薄膜放大器一體整合之觸覺感測面，其電壓訊號放大為10倍，訊雜比則提升至66分貝。採用氧化鋅壓電薄膜的觸覺感測面也製作於可撓性聚醯亞胺塑膠基板上，具有與在玻璃基板上的感測面有類似的增益和訊雜比，結果顯示此觸覺感測面能成功的偵測觸壓事件。

關鍵字

薄膜電晶體 ； 薄膜放大器電路 ； 壓電感測薄膜

並列摘要

In this research, flexible complimentary metal-oxide-semiconductor (CMOS) inverters and circuits based on oxide thin-film transistors (TFTs) are developed. At first, CMOS inverters composed of n-channel zinc oxide (ZnO) and p-channel tin monoxide (SnO) TFTs are demonstrated on polyimide foil substrates. The inverted-staggered bottom-gated TFTs are fabricated by a low-temperature rf-sputtering technique. The static voltage gain of a flexible oxide-TFT-based CMOS inverter with a geometric aspect ratio of 5 is ~12 at a supplied voltage (VDD) of 12 V. The electrical performances of devices under various mechanical strain levels are investigated. Degradations of TFTs and inverters are observed when mechanical tensile strains are applied, whereas the influence of compressive strain is negligible.
We further demonstrate complementary oxide-TFT-based inverters with p-channel SnO and n-channel SnOx TFTs via the single-step deposition of the active layer technique. The modulation of charge carrier polarity is realized by selective deposition of a capping layer on top of the n-channel active layer as an oxygen source. Evolution of transfer characteristics from p-type character to n-type character with the increase of annealing time for the n-channel SnOx TFT with the ZrO2 capping layer is observed. The optimal annealing time is 60 min, where the achieved static voltage gain is 13 at VDD of 10 V for both on-glass and on-PI inverters. A similar degradation is observed when the on-PI SnOx-based complementary inverter is subjected to mechanical tensile strains.
Due to the low switching threshold voltage of the SnOx-based complementary TFT inverter, a thin-film amplifier for piezoelectric sensor films is constructed using a complementary inverter composed of SnO and ZnO TFTs with a feedback resistor to ensure a high gain. The amplifier is used to increase the signal level and robustness of the polyvinylidene difluoride (PVDF) and ZnO piezoelectric sensor films. The on-glass amplifier can enlarge the output voltage level by a factor of 10, while the gain of the on-PI amplifier is around 6 V/V. Signal-to-noise ratios (SNRs) do not increase as the amplifier is used, which implies external wiring causes signal loss and introduces noises.
A tactile sensing surface is fabricated on a glass substrate to demonstrate the integration feasibility of the piezoelectric sensor films with the readout amplifiers. The tactile sensing surface contains 4 individual sensing areas, and each area is made of a piezoelectric sensor film and a readout amplifier. The sensing surface with PVDF piezoelectric sensors exhibits an enhancement of signal level by a factor of 11 and a SNR of 32 dB. The sensing surface with ZnO piezoelectric sensors exhibits an enhancement of signal level by a factor of 10 V/V and a SNR of 66 dB. The tactile sensing surface is further demonstrated on a flexible substrate with comparable level of gain and SNR. The resulting tactile sensing surface ensures successful detection of touch events.

並列關鍵字

Thin-Film Transistor ； Thin-Film Amplifier Circuit ； Piezoelectric Sensor Film

參考文獻

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