以水合蛋白質作為閘極介電層之有機場效應電晶體的特性探討

Investigation of organic field-effect transistors with hydrated proteins as gate dielectric

蔡立軒(Li-Shiuan Tsai)

指導教授 ： 黃振昌

國立清華大學/工學院/材料科學工程學系/博士(2014年)

摘要

本論文研究水合蛋白質介電層在有機場效應電晶體的應用，並探討水合蛋白質內移動離子對電晶體特性的影響。在2nm的五苯環夾層幫助下，以蠶絲蛋白作為介電層的碳六十有機場效應電晶體在真空中的飽和區載子遷移率可以從0.014 cm2V-1s-1提升至1 cm2V-1s-1。當碳六十有機場效應電晶體從真空取出，置於相對溼度55%的大氣時，飽和區載子遷移率可以進一步的提升至10 cm2V-1s-1。大氣中載子遷移率大幅提升的原因是蠶絲蛋白與水氣反應產生移動離子，讓電晶體在操作時，累積額外的電荷於導電通道內造成元件特性的改變。
研究發現水合蛋白質在大氣環境下會與水氣反應產生移動離子，造成電晶體的電性變化。在不同的相對濕度下，含蠶絲蛋白介電層之五苯環有機場效應電晶體會有不同的元件特性。當環境的相對溼度為70%，蠶絲蛋白內移動離子的數量較多，介電層電容和臨界電壓分別為100 nF/cm2和-0.9V。當相對濕度降低至40%時，移動離子減少，電容值下降至15nF/cm2，臨界電壓提升至-4V。電晶體來回掃描時的遲滯現象也受到移動離子數量的影響。相對溼度為40%的遲滯電壓位移約為4V，當相對濕度提高至50%和70%時，移動離子的數量增加，使得離子的移動能力提高，遲滯電壓位移下降為1.7V和1.3V。
由於蠶絲蛋白內離子的遷移需要時間，使用不同閘極偏壓掃描頻率的量測，五苯環有機場效應電晶體擁有不同的元件特性。高掃描頻率的量測會使得離子不及反應，讓電晶體擁有較高的臨界電壓和遲滯電壓位移，分別為-1.7V和2.6V。當掃描頻率降低至0.08V/s時，臨界電壓和遲滯電壓位移減少為-0.6V和0.5V。使用TTC鈍化層鈍化蠶絲蛋白表面，可以減少移動離子對電晶體特性的影響，讓掃描頻率對遲滯現象和臨界電壓的影響降低。
使用不同的掃描頻率量測以明膠蛋白作為閘極介電層的五苯環有機場效應電晶體，可以得到與蠶絲蛋白作為介電層類似的電性變化趨勢，主要原因是明膠蛋白在大氣中也會產生移動離子，電晶體在運作時才會有類似的電性表現。
以蠶絲蛋白作為介電層，結合n型的碳六十與p型的五苯環組成碳六十/五苯環雙層型有機場效應電晶體，在大氣中擁有良好的雙載子特性。良好的雙載子特性除了蠶絲蛋白內移動離子的貢獻外，電晶體的元件結構也是重要的因素。選用五苯環作為下層半導體，以及碳六十作為上層半導體的元件結構時，五苯環成長於蠶絲蛋白上，而碳六十則是成長於五苯環上，有助於兩者形成高結晶性薄膜且擁有高載子遷移率。在調整半導體層厚度與控制製程溫度後，可以進一步得到匹配的電子與電洞遷移率，分別為10 cm2V-1s-1和11.5 cm2V-1s-1。
連結兩個六十/五苯環雙載子有機場效應電晶體組成的雙載子反向器擁有開關特性，且可以正常運作於第一象限和第三象限的操作區間中。

關鍵字

有機場效應電晶體 ； 五苯環 ； 碳六十 ； 水合蛋白質 ； 雙載子有機場效應電晶體

並列摘要

In this thesis, we report the electrical characteristics of several organic field-effect transistors using hydrated protein as gate dielectric, and the mechanism of mobile ions in hydrated proteins is proposed. With the assistance of 2nm pentacene interlayer, the moblilty(μFE) of C60 OFET using silk fibroin as gate dielectric is improved from 0.014 cm2V-1s-1 to 1 cm2V-1s-1 in vacuum. The μFE value of the C60 OFET is further enhanced to 10 cm2V–1s–1 when the OFET is exposed to air in a relative humidity of 55 %. The enhancement of μFE is due to the generation of mobile and immobile charged ions in silk fibroin in air ambient, and additional charge carriers are accumulated in the conduction channel in OFETs operation.
Generation of mobile ions in hydrated proteins may influence the chararteristics of OFETs. The characteristics of pentacene OFETs using silk fibroin as gate dielectric maybe changed at different relative humidity. At a relative humidity of 70%, the amount of mobile ions in silk fiborin is large, the dielectric capacitance and threshold voltage are 100 nF/cm2和-0.9V, respectively. The dielectric capacitance is reduced to 15 nF/cm2 and threshold voltiag is increased to -4V when the relative humidity is reduced to 40%.
The hysteresis of pentacene OFETs is affected by the migration of ions in the silk fibroin. The voltage shift between forward and backward sweeps of gate voltage is 4V at a relative humidity of 40%, and the voltage shift is respectively reduced to 1.7V and 1.3V when the relative humidity is increased to 50% and 70%.
Since the ions migration in the silk fibroin is a time dependent effect, OFETs operated at different gate voltage sweep rates exhibit different characteristics. At the high sweep rate, the threshold voltage and hysteresis shift are -1.7V and 2.6V, respectively. When the sweep rate is further reduced to 0.08V/s, the threshold voltage and hysteresis shift are reduced to -0.6V and 0.5V. Using tetratetracontane(TTC) layer inserted into the silk fibroin and pentacene bilayer structure, the effect of mobile ions in OFETs opreration may be reduced.
The device characteristics of pentacene OFETs using gelatin as gate dielectric at different sweep rates have the same tendency as that using silk fibroin as gate dielectric. The main reson to obtain similar results is due to the ion migration in the hydrated proteins.
The C60/pentacene ambipolar OFETs using silk fibroin as gate dielectric exhibit excellent performance in the air ambient. Stacking sequence of semiconductor is another factor for good performance of ambipolar OFETs. In our transistor structure, pentacene is deposited on silk fibroin and C60 is deposited on pentacen layer. The sequence of semiconductors helps to get well crystalized pentacene and C60 and the μFE values of holes and electrons are increased. The electron and hole mobility are 10 cm2V-1s-1 and 11.5 cm2V-1s-1, respectively, for a bilayer of 20nm C60 /10nm pentacene and the deposition temperature is 70℃for C60 and 25℃ for pentacene.
An ambipolar inverter made with two C60/pentacene ambipolar OFETs exhibits normal swithing characteristics in both the first and third quadrants.

並列關鍵字

Organic field-effect transistor ； Pentacene ； C60 ； Hydrated protein ； Ambipolar organic field-effect transistor

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