Chun Ying Chen

High field-effect-mobility a-Si:H TFT based on high deposition-rate PECVD materials

The hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) having a field-effect mobility of 1.45 /spl plusmn/0.05 cm/sup 2//V/spl middot/s and threshold voltage of 2.0/spl plusmn/0.2 V have been fabricated from the high deposition-rate plasma-enhanced chemical vapor deposited (PECVD) materials. For this TFT, the deposition rates of a-Si:H and N-rich hydrogenated amorphous silicon nitride (a-SiN/sub 1.5/:H) are about 50 and 190 nm/min, respectively. The TFT has a very high ON/OFF-current ratio (of more than 10/sup 7/), sharp subthreshold slope (0.3/spl plusmn/0.03 V/decade), and very low source-drain current activation energy (50/spl plusmn/5 meV). All these parameters are consistent with a high mobility value obtained for our a-Si:H TFT structures. To our best knowledge, this is the highest field-effect mobility ever reported for an a-Si:H TFT fabricated from high deposition-rate PECVD materials.

Gated-four-probe a-Si:H TFT structure: a new technique to measure the intrinsic performance of a-Si:H TFT

In this letter, a new technique based on gated-four-probe hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) structure is proposed. This new technique allows the determination of the intrinsic performance of a-Si:H TFT without any influence from source/drain series resistances. In this method, two probes within a conventional a-Si:H TFT are used to measure the voltage difference within a channel. By correlating this voltage difference with the drain-source current induced by applied gate bias, the a-Si:H TFT intrinsic performance, such as mobility, threshold voltage, and field-effect conductance activation energy, can be accurately determined without any influence from source/drain series resistances.

Investigation of intrinsic channel characteristics of hydrogenated amorphous silicon thin-film transistors by gated-four-probe structure

We use a new hydrogenated amorphous silicon (a-Si:H) device structure, the gated-four-probe a-Si:H thin-film transistor (TFT), to investigate the intrinsic channel characteristics of inverted-staggered a-Si:H TFTs without the influence of source/drain series resistances. The experimental results have shown that, for the conventional a-Si:H TFT structure, the field-effect mobility, threshold voltage, and field-effect channel conductance activation energy have a strong dependence on a-Si:H thickness and TFT channel length. On the other hand, for the gated-four-probe a-Si:H TFT structure, these values are a-Si:H thickness and TFT channel length independent, clearly indicating that this new a-Si:H TFT structure can be effectively used to measure the channel intrinsic properties of a-Si:H TFTs.

Gated four-probe TFT structure: a new technique to measure the intrinsic performance of a-Si:H TFT

A new technique to determine the intrinsic performance of hydrogenated amorphous silicon thin film transistor (TFT) without any influence from source/drain series resistances is proposed. This technique is based on a-Si:H gated-four- probe (GFP) TFT structure. In this method, two probes within the channel of a conventional inverted-staggered a-Si:H TFT are used to measured the voltage difference. By correlating this voltage difference with the drain-source current induced by applied gate bias, the intrinsic performance of a-Si:H TFT, such as mobility, threshold voltage and field- effect conductance activation energy, can be accurately determined without influence from the source/drain series resistances. The a-Si:H GFP TFT and conventional a-Si:H TFT structures are also analyzed and their properties are compared by using 2D simulation based on finite element method. The influence of series resistances on a-Si:H TFT electrical performance is clearly described from the simulation results.

Surface potential study of amorphous In-Ga-Zn-O thin film transistors

In this paper, we report on surface potentiometry in the channel region of operating amorphous In–Ga–Zn–O thin film transistors by scanning kelvin probe microscopy. Important parameters including the field-effect mobility and source/drain contact resistance are extracted from the channel potential profile. We find that the channel potential as a function of gate/drain bias can be described by the standard metal oxide semiconductor field effect transistor (MOSFET) equation incorporated with two nonideal factors: the gate-voltage-dependent field-effect mobility and the source/drain contact resistance.

Schottky-contact gated-four-probe a-Si:H TFT structure: a new structure to investigate the electrical instability of a-Si:H TFT

In this letter, we describe a new device structure, the Schottky-contact (SC) gated-four-probe (GFP) hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) structure, that can be used to study the electrical instability of a-Si:H TFTs induced by bias-temperature-stress (BTS). In this SC-GFP TFT structure, the evolution of both electron and hole conduction characteristics can he studied before and after BTS without the influence of source-drain contacts. We observed that low-bias negative stress induces a reduction in the deep-gap state density, while high-bias negative stress mainly causes trapping of holes in the gate-insulator. On the other hand, positive BTS induces mainly the trapping of electrons in the gate-insulator, which causes positive shifts of both electron and hole conduction characteristics.

High-Rate Deposited Amorphous Silicon Nitride for the Hydrogenated Amorphous Silicon Thin-Film Transistor Structures

Hydrogenated amorphous silicon nitride thin films, prepared in a large area plasma-enhanced chemical vapor (PECVD) deposition system utilizing high-rate deposition technique, have been characterized by various techniques. Experimental data obtained from this study are presented and compared to low-rate deposited PECVD films. Special attention has been devoted during this study to the difference between high- and low-rate deposited samples. The amorphous silicon (a-Si:H) thin-film transistors (TFTs) based on high-rate PECVD materials have been fabricated and characterized. The evaluation of a-Si:H TFTs indicates a good electrical performance which is comparable to its low-rate PECVD materials counterparts.

Study of the Density of States of a-InGaZnO Using Field-Effect Technique

This paper studies the density-of-localized gap states (DOS) for RF sputter amorphous InGaZnO (a-IGZO) as determined from temperature dependent study of the a-IGZO thin film transistor (TFT) electrical properties. Measurements were performed on inverted-staggered RF sputter a-IGZO TFTs. The drain current (ID) versus the gate-to-source voltage (VGS) at different temperatures from 30degC up to 90degC were measured. Calculated DOS from the subthreshold regime appears to be low with a characteristic energy of about 110 meV. The DOS is larger and has a steeper slope with a characteristic energy of about 30 meV.

Simulation of influence of density of states in a-Si:H on electrical performance of a-Si:H thin-film transistors

A two-dimensional analysis of the density of states in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) is simulated by Semicad Device program. The model of the density of states in a-Si:H consists of conduction-band and valence-band-tail states, and deep-gap states. We found that mobility is sensitive to the conduction-band-tail states and threshold voltage is mainly determined by the combination of the deep-gap states, interface states and fixed charges, which are localized at or near the gate insulator/a-Si:H interface. We have also analyzed the physical origin of the nonlinearity of current-voltage characteristic of a-Si:H TFT. The influence of top and bottom gate insulator/a-Si:H interfaces on TFT performance are compared.

High field-effect-mobility a-Si:H TFT based on high deposition-rate materials

Summary form only given. The hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) with field-effect mobility (/spl mu//sub FE/) of 1.5 cm/sup 2//V/spl middot/s and threshold voltage (V/sub /spl tau//) of 1.9 V have been fabricated using the high deposition-rate plasma-enhanced chemical vapor deposited (PECVD) materials. To the best of our knowledge, this is the highest field-effect mobility ever reported for a-Si:H TFT made from high deposition-rate materials.