Professor Lung-Han Peng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 彭隆瀚教授

We reported the direct current (DC) and radio frequency (RF) transport properties measured on - GaN/Ga₂O₃ single nanowire (SNW)-MOSFET devices. The devices were laterally- and directionally- grown on (0001) sapphire substrates using a home-built reactor invoking the gold-catalyst vapor-liquid-solid growth mechanism. For a 60nm-dia. Ga₂O₃/GaN SNW-MOSFET of 0.1mm gate length and drain-source distance of 1mm, we measured a saturation current of 160mA, current on/off ratio of 10⁵, swing of 85mV/dec, transconductance of 85mS, and cut-off frequency f_t/f_max of 95/105 GHz, respectively. From these measurements we identify the observation of electric mitigation over the short-channel effects such as V_t roll-off and improvement of S factor owing to the nanowire device aspect ratio effect similar to their III-V planar counterpart FET devices. These improved transport properties were ascribed to the high-crystallinity and abrupt interfaces between sapphire/GaN and GaN/Ga₂O₃ as verified from the high-resolution transmission electron microscopy (HRTEM) analysis. From a 3D diffusion and drift model analysis, we reconstructed the transistor’s current-voltage (I-V) characteristics by incorporating a sheet of high mobility (m = 1000 cm²/V-sec) electron gas (2DEG) of 7´10¹² cm^-2 confined at the GaN/Ga₂O₃ interface. It proves the origin of 2DEG confined at the semi-polar GaN/Ga₂O₃ interface is caused by the discontinuity of the spontaneous polarization P_sp effect to screen out the polarization-induced fixed charge therein. Its magnitude conforms to a law of cosine dependence (q = 62°) to the bulk GaN P_sp value of
-0.029C/m². These observations illustrate the virtues of using a simple architecture of Ga₂O₃/GaN NW-MOSFET structure to pursue the scaling-down issues of integrating the III-V nano-transistors on the silicon-based CMOS platform.
Ref: C.-W. Yu et al., Appl. Phys. Lett. 99, 152108 (2011)

 Professor Chung-Chih Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 吴忠帜教授

We have been dedicated to development of oxide semiconductor thin film transistors (TFTs) in recent years due to their various merits, such as high mobility in amorphous phase, low processing temperature and transparency etc., promising for various novel applications. (1) We had developed high-performance transparent oxide TFTs (Fig. 1) based on amorphous In-Ga-Zn-O (a-IGZO) with a mobility m of up to 45 cm²/V×s, a sub-threshold swing SS of 0.4 V/decade, an on/off ratio of >10⁷, and good stability (small DV_th of <0.2 V after extended current stressing). Active-matrix OLED displays using such oxide TFTs had also been demonstrated in a collaboration work. (2) We had also developed high-performance and highly flexible a-IGZO TFTs on fully transparent polyimide-based nanocomposite substrates (Fig. 2) using conventional micro-fabrication processes that are compatible with existing production technologies. The flexible a-IGZO TFTs exhibited a decent m of up to 16 cm²/V×s, a SS of 0.4 V/decade and an on/off ratio of >10⁸. The devices could be bent down to a radius of curvature of 3 mm and yet remained normally functional, with only small changes of TFT characteristics vs. applied strains (compared to a-Si). (3) In addition to device technologies, we had also developed the physical modeling of carrier transport and the subgap density of states in amorphous oxides for device simulation of oxide TFTs operated in both the depletion/enhancement modes, which shall be of general use for designs of oxide TFT devices and circuits (Fig. 3).

Fig. 1. (a) Photo of transparent oxide TFTs. (b) Output and transfer characteristics of transparent a-IGZO TFTs. (c) Prototype AMOLED using a-IGZO TFTs.

Fig. 2. (a) Photo of micro-fabricated flexible a-IGZO TFTs on transparent polyimides. (b) Output characteristics of flexible a-IGZO TFTs. (c) Flexible a-IGZO TFT characteristics vs. bending radius. (d) Flexible a-IGZO TFT mobility vs. strain.

Fig. 3. (a) Physical modeling a-IGZO TFTs. (b) Tight fits of measured TFT characteristics with simulation. (c) Extracted subgap density of states of amorphous oxide semiconductors.

姓名：蔡志宏   指导教授：吴忠帜教授

论文题目：以光致电化学蚀刻技术制作氮化物发光组件

姓名：林政宏   指导教授：杨志忠教授

— 数据提供：影像显示科技知识平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃岩教授、陈圣灏 —

光流体：可调式微透镜（Optofluidics: Tunable microlenses）

具有可调焦距功能的光流体微透镜，可以利用于光蚀刻、光学成像以及在芯片上作细胞分选与检测等应用。目前利用外加电场或电湿式达成之可调焦距技术，通常会造成光学像差、液体蒸发、反应速度较慢以及可调范围狭窄等问题。

藉由多层堆栈之软蚀刻(soft lithography)技术（一种广泛用于制作高度集成(highly integrated)大尺度之微流体芯片之技术），北京大学的Yanyi Huang与其同事已经发展出一种具备可挠、可调性质并具有强度之化合物微透镜(Lab Chip, 2835–2841; 2011)。

研究人员利用三层由有机多分子聚二甲基硅氧烷(polydimethylsiloxane)所组成水平层制作出一具有许多微通道(micro-channel)之芯片，每一层皆含有一圆形腔槽连接其中的一条通道，由此通道进行液体注入的工作。在中间层的部分，多个方形腔槽被连接到直径为700 μm的圆形腔槽以整合作为气动阀门。阀门被用来决定腔槽中液体的体积进而用以调整微透镜之焦距，研究人员指出微透镜之折射率也可利用不同的注入液体以作调整。

图一：流体透镜及其工作原理示意图

由化合物所制造出之微透镜具有许多吸引人之特性，包含了自对准功能(self-alignment)、较大之变焦比( ~7x)、可调范围大之广视角(15–80°)、较大之聚焦范围(从次毫米到公分)、较大之数值孔径(可达到0.44)、小体积(直径约为几百个微米)以及变焦反应时间约在100毫秒范围。

根据这个研究，其制造方法不仅克服了几十年来在光流体微透镜的研究者所遭遇的许多挑战，且开启了制作其它种类之可调式微光学组件的可能性。