壓電材料之極化翻轉能力研究及其在光致熱元件的應用

Polarization switching capability of piezoelectric materials and their applications in optothermal devices

謝俊儀(Chun-Yi Hsieh)

指導教授 ： 陳永芳

共同指導教授 ： 施惟恒 ； 楊完

國立臺灣大學/理學院/物理研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.00852

摘要

在本論文中，我們先報告了在壓電材料中所觀察到的特殊現象，之後並製造了以鐵電材料的焦電特性為主的光電元件。最後，我們著手了結合壓電和焦電特性的研究。相信我們的研究對於鐵電材料的應用開創了新的道路。
1.在無基底壓電薄膜上所觀測到外加反向電場所造成的兩階段極化翻轉現象
藉由壓電力顯微鏡可發現外加反向電場下無基底鈦酸鉛鈮鎂薄膜之極化轉變行為，此極化翻轉過程包含兩階段：首先，在反向電場< 5 kV/cm時，極化方向會從法線方向翻轉至平面方向；接著，在反向電場>5 kV/cm時，極化方向會從平面方向翻轉至與電場方向相反。在反向電場等於5 kV/cm時所發生的極化容易轉至平面的現象歸咎於薄模幾何結構的影響，此時也代表薄膜有最大的介電常數。
2.藉由雷射加熱過程在壓電材料-鈦金屬複合懸樑上產生電壓的效應
將環境中的熱能轉換成電能具有很大的好處。由壓電材料所構成的壓電複合懸樑(PUC)已被證實是一個很有效的生物感測元件以及彈性映圖工具。這裡我們展示了壓電懸樑(PUC)可以有效地把熱能轉換成電能。結合焦電以及壓電的性質，由鋯鈦酸鉛與鈦金屬構成的壓電懸樑在雷射的照射之下產生了比單層鋯鈦酸鉛懸樑還大的感應電壓。這種結構提供了一個很有效的方式把熱能轉換成電能。
3.由石墨稀-鋯鈦酸鉛構成的高靈敏度光致熱場效電晶體
我們研發了一種以石墨烯和鋯鈦酸鉛所組成的新型焦電場效應電晶體(FET)。藉由雷射光的照射之下，光致熱效應調變了場效電晶體的電導。當入射雷射光時，鋯鈦酸鉛基板的極化的方向決定了汲極電流是會增加或減少。在電場為6.7 kV/m 時，光致熱場效電晶體的汲電流靈敏度可到達360 nA/mW，是大於焦熱反應所產生電流達三個數量級，甚至也大於由光-控制二氧化矽/矽基板上的奈米碳管電晶體所產生的電流達五個數量級。這是因為焦電場效電晶體上的石墨烯具有高導電性和高透明性所造成極好的效果。
4.單根氧化鋅奈米線與鋯鈦酸鉛構成的光致熱效應電晶體
單根的氧化鋅奈米線與鋯鈦酸鉛的複合結構(ZnO NW-PZT)所形成新型焦電場效電晶體(FET)已發展出來，經由紅外線雷射的照射，光致熱效應可以調變電導。在紅外雷射的照射之下，依據鋯鈦酸鉛基板的極化方向，可以讓電流有增加或減少的行為。藉由結合紫外光波段的光電流以及紅外線範圍的光致熱效應，讓光調變單根氧化鋅奈米線與鋯鈦酸鉛所組成的電晶體電流有較廣的光譜響應，並且在奈米光電元件的領域上開創了新的道路。

關鍵字

極化翻轉 ； 無基底壓電薄膜 ； 懸樑 ； 焦電性 ； 光致熱場效電晶體

並列摘要

In this thesis, we first reported the investigation of polarization properties of piezoelectric material due to electric field and laser heating followed by the fabrication of optoelectronic devices based on those properties. It is believed that our studies shown here may open up a new route for the application of ferroelectric materials.
1.Direct observation of two-step polarization reversal by an opposite field in a substrate-free piezoelectric thin sheet
The domain switching behavior of a substrate-free lead magnesium niobate-lead titanate thin sheet by an opposite electric field (E) was examined by piezoresponse force microscopy. It is shown that the polarization reversal process involved two steps. First the polarization switched from the initial normal direction to an in-plane direction at -E < 5 kV/cm. Second, at -E > 5 kV/cm, the polarization was further switched from the in-plane direction to the opposite field direction. The preference of the in-plane polarization at -5 kV/cm was attributed to the thin-sheet geometry, which also manifested itself as a maximum in dielectric constant at the same field.
2.Voltage generation from piezoelectric-titanium unimorph cantilever by laser heating
Converting ambient thermal energy into electricity is of great interest in harvesting energy from the environment. Piezoelectric unimorph cantilevers (PUC) have previously been shown to be an effective biosensor and a tool for elasticity mapping. Here we show that PUC can be efficiently used to convert heat to electricity. By combining pyroelectric and piezoelectric feature, PZT-Ti bi-layer cantilever showed an enhanced induced voltage under laser heating, comparing to that of PZT layer alone. This type of device provides an efficient way for converting heat energy into electricity.
3.Highly sensitive graphene-PZT optothermal field effect transistors
We have developed a new type of pyroelectric field effect transistor (FET) based on a graphene-lead zirconate titanate (PZT) system. Under the incidence of a laser beam, the transconductance of FET can be varied by optothermal gating. The drain current can be increased or decreased by the laser light depending on the direction of the polarization of the PZT substrate. The drain current sensitivity of the optothermal FET can reach up to 360 nA/mW at a drain field of 6.7 kV/m which is 3 orders of magnitude larger than the pyroelectric current sensitivity and more than 5 orders of magnitude higher than that of the photogating transistors based on carbon nanotube on SiO2/Si substrate. Due to its high optical transparency and conductance graphene is an excellent component for the pyroelectric FET.
4.Single ZnO nanowire-PZT optothermal field effect transistors
A new type of pyroelectric field effect transistor (FET) based on a composite consisting of single zinc oxide nanowire and lead zirconate titanate (ZnO NW-PZT) has been developed. Under infrared (IR) laser illumination, the transconductance can be modulated by optothermal gating. The drain current can be increased or decreased as operated by IR illumination depending on the polarization orientation of the PZT substrate. Furthermore, by combining the photocurrent feature in the UV range and the optothermal gating effect in IR range, the wide range spectrum response of the tunable current modulated by light based on single ZnO NW-PZT transistors opens up a new route for the development of nanoscale optoelectronic devices.

並列關鍵字

Polarization reversal ； Substrate-free piezoelectric thin sheet ； Cantilever ； Pyroelectricity ； Optothermal FET

參考文獻

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