光電所所訊

Complementary Oxide-TFT-Based Circuits with N-Channel ZnO and P-Channel SnO Thin-Film Transistors

Professor I-Chun Cheng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所陳奕君教授

Complementary thin-film transistor (TFT) circuitry consisting of inverters is the building block for realizing integrated logic circuits on large-area and/or flexible substrates. Although numerous oxide-TFT circuits have been reported previously, most of them were based on n-channel MOSFET (NMOS) technology, implying that the development of p-channel oxide-TFTs with sufficient satisfactory performance via a low-temperature process is crucial. In this study, we report, for the first time, fully oxide-TFT-based complementary metal-oxide-semiconductor (CMOS) ring oscillators by using large–area-compatible sputtering processes. The p-channel tin monoxide (SnO) and n-channel zinc oxide (ZnO) TFTs used in the CMOS inverter have inverted-staggered bottom-gate structures. The SnO TFT exhibits a threshold voltage (V_th) of 3.5 V, field-effect mobility of 0.33 cm²/V-s, sub-threshold swing (S.S.) of 2.5 V/decade, and on/off current ratio of ~10³. The corresponding values for the ZnO TFT are 6.22 V, 3.5 cm²/V-s, 350 mV/decade, and >10⁶. The achieved voltage gain of the CMOS inverters is ~17 at a supplied voltage (V_DD) of 10 V when the geometric aspect ratio is 5. An oscillation frequency of 2 kHz is obtained from a five-stage oxide-based CMOS voltage control oscillator at V_DD of 14 V. The result shows the feasibility of realizing fully oxide-TFT-based CMOS circuits.



Fig. 1. (a)(b) Transfer and (c)(d) output characteristics of the p-channel SnO TFT (W/L = 60 μm/30 μm) and ZnO n-channel TFT (W/L = 30 μm/30 μm), respectively. The linear field-effect mobilities as a function of gate voltage for SnO and ZnO TFTs are plotted in (a) and (b), respectively.


Fig. 2 (a) The static voltage transfer characteristics and voltage gain curves at different supply voltages (V_DD) of the complementary oxide-TFT inverter with a geometric aspect ratio, (W/L)_p/(W/L)_n, of 5. (b) Output waveform of a five-stage ring oscillator based on complementary oxide-TFT inverters at V_DD = 14 V.

Development of numerical modeling program for organic/inorganic hybrid solar cells by including tail/Interfacial states models

Professor Yuh-Renn Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所吳育任教授

A simulation software is developed for modeling the organic/inorganic hybrid solar cells. Firstly, the optical field in the solar cell device is calculated by using the two-dimensional finite-difference time-domain (2D-FDTD) method. By solving the Poisson’s and drift-diffusion equation which utilizes the finite element method (FEM), the electrical properties of the device can be obtained. A Gaussian distribution function of tail states is addressed to simulate the carrier transportation in the organic material. These tail states located around the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of the organic material provides a path way for carriers to hop in and transport through the organic material. In this research, a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/silicon nanowire (SiNW) hybrid solar cell is set up as the simulation model. The validity of the software is verified by comparing the simulated J-V curve with experimental J-V curves. The electrical and optical properties are analyzed for further optimization.

Fig. 1. The simulated band diagrams of the PEDOT:PSS/SiNW hybrid solar cells.

Fig. 2. The generation rate of the PEDOT:PSS/SiNW hybrid solar cells calculated by 2D-FDTD.