P-channel Mode Research Articles

Schottky barrier thin-film transistor (SBTFT) with silicided source/drain and field-induced drain extension

A novel Schottky barrier thin-film transistor (SBTFT) with silicided source/drain and field-induced drain (FID) extension is proposed and demonstrated. In the new device configuration, a metal field-plate (or sub-gate) lying on the passivation oxide is employed to induce a sheet of carriers in a channel offset region located between the silicided drain and the active channel region underneath the main gate. The new device thus allows ambipolar device operation by simply switching the polarity of the bias applied to the field plate. In contrast to the conventional SBTFT that suffers from high GIDL (gate-induced drain leakage)-like off-state leakage current, the new SBTFT with FID is essentially free from the GIDL-like leakage current. In addition, unlike the conventional SBTFT that suffers from low on-off current ratio, the new device exhibits high on/off current ratio up to 10/sup 6/ for both n- and p-channel modes of operation. Moreover, the implantless feature and the ambipolar capability of the new device also result in extra low mask count for CMOS process integration. These excellent device characteristics, coupled with its simple processing, make the new device very promising for future large-area electronic applications.

High-sensitivity phthalocyanine LB film gas sensor based on field effect transistors

A new kind of symmetrically substituted copper phthalocyanine derivative was synthesized. Metal-oxide-semiconductor field effect transistors (MOSFET) were designed for the measurements of FET characteristics. At the same time, oxide-semiconductor field effect transistors (OSFET) were specially designed with a long gate area for the measurements of gas sensitivity of phthalocyanine LB film. To obtain high sensitivity of the Langmuir–Blodgett (LB) gas sensor, FETs with depletion(D) p-channel mode were selected to be fabricated on the same monolithic silicon. LB multilayer films of copper phthalocyanine (CuPc) were later transferred to the long gate area of OSFET(D), forming the structure of LB-OSFET(D). The measurement of gas sensitivity for the LB-OSFET(D) sensor showed that higher sensitivity to NO 2 could be obtained because of the effect of exhausted mode used in FET. This sensor can detect NO 2 up to 0.1 ppm; it also exhibits good stability, excellent selectivity, and rapid response and recovery.

Transient effects in accumulation mode p-channel SOI MOSFET's operating at 77 K

This paper critically examines the conduction mechanisms in accumulation mode p-channel SOI MOSFET's operating at cryogenic temperatures. In particular, attention is given to the body current component, which in most cases is experimentally not observed at 77 K or 4.2 K. As will be demonstrated, both the body current and the back accumulation current show pronounced transient effects at low temperatures, which are related to the slow generation/recombination of minority carriers. This is caused by deep depletion from the front interface, which suppresses these current components. By the application of either a light pulse or a large drain voltage V/sub ds/ minority carriers are generated nearly instantaneously in the body region, rendering the body and the back accumulation components clearly visible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermal-CVD Produced Amorphous-Silicon Thin-Film Transistors-Ambipolar Characteristics

ABSTRACTAmorphous-silicon thin-film transistors (a-Si TFTs) have been fabricated by using an a-Si layer deposited by low-temperature thermal-CVD method using higher silanes. The TFT with thermally grown SiO2 gate was operated in both the n-channel mode and the p-channel mode. The maximum field-effect mobility and typical on/off current ratio were 1.5 cm2/Vs and 107 for the n-channel operation, and 0.2 cm2/Vs and 106 for the p-channel operation, respectively. Free electron mobility in the conduction band and free hole mobility in the valence band have been estimated, using the temperature dependence of the field-effect mobilities. It was found that the hole mobility is as high as the electron mobility.

An accurate CAD model for the ambipolar a-Si: H TFT

The ambipolar output drain current versus drain voltage characteristics of hydrogenated amorphous silicon thin-film transistors are modeled by a method intended for use in computer-aided design programs. An accurate model has been developed that uses a modified experimental sheet conductivity curve to predict the output drain characteristics over many orders of magnitude of the drain current in both the n-channel and p-channel modes of operation. Analytical expressions for the drain current are developed.

Elementary ambipolar field-effect transistor model

An ambipolar FET can be operated alternatively in n-channel and p-channel modes. A simple conceptual model is proposed. It considers ohmic source and drain contacts, a gradual channel, and the depletion approximation.

Comparison of different techniques for passivation of small-grain polycrystalline-Si MOSFET's

Different hydrogen passivation techniques have been investigated and correlated with the device characteristics of accumulation mode p-channel MOSFET's fabricated in small-grain polycrystalline Si (poly-Si). The dependence of characteristics on a) annealing time and temperature, b) different poly-Si deposition conditions, and c) different encapsulation layers has been studied. Using hydrogenation by ion implantation with a subsequent anneal of 10 min at 400°C or an anneal of 25s at 450°C in the presence of a top encapsulating LPCVD Si 3 N 4 layer, MOSFET's with ON/OFF current ratio of 4 × 107have been obtained with drain-to-source voltage of -5 V.

SOI-CMOS devices on beam-recrystallized polysilicon

Control of the grain boundary direction in the recrystallized polycrystalline silicon (polysilicon) island is achieved by the direction of the laser scanning. By using this technique, the source-to-drain short in a short-channel MOSFET is almost eliminated, and MOSFETs with channel lengths of 2–3 μm level in both n-channel and p-channel mode are fabricated with a good uniformity and reproducibility. The low-field electron and hole mobilities are 580 cm 2/Vsec and 220 cm 2/Vsec, respectively. 19-stage CMOS ring oscillators with nominal channel lengths of 3μm are fabricated. The minimum propagation delay is 280 psec/stage at a supply voltage of 10 V, and the minimum power delay product is 0.13 pJ/stage.

High-performance amorphous-silicon field-effect transistors

p-channel and n-channel amorphous-silicon field-effect transistors with thermally grown SiO2 as a gate insulator have been investigated. On-off current ratios of 4×106 and 105 were obtained for n- and p-channel modes, respectively, and the electron and hole mobilities were about 0.1 and 2×10−3 cm2/V/s, respectively.

“MFS FET” -A New Type of Nonvolatile Memory Switch Using PLZT Film

A step-like change in the interface built-in potential by controlling the ferroelectric polarization has been observed in PLZT thin film sputtered on GaAs single crystal heterostructure junction. We have developed a nonvolatile memory FET by using this MFS (Metal-Ferroelectric-Semiconductor) construction. A typical performance of the GaAs device with a p-channel mode operation is that the writing (“0” to “1” threshold) gate voltage Von=1.5 V, the erasing (“1” to “0”) gate voltage Voff=6.0 V, and the on state drain current Ion=0.1 mA. This operation power level obtained here is about one order of magnitude smaller than that of similar type devices using other ferroelectrics such as Bi4Ti3O12, PZBFN and SbSI. A series of technical data for the fabrication technologies including thin film deposition of the ferroelectric are presented, and the analyses on the device performance are also discussed.

MOLYBDENUM FILMS AS PARTIAL DIFFUSION MASKS IN MOS PROCESSING

Thin molybdenum films ∼1000 Å deposited on thermal SO2 grown on Si are observed to act as partial masks for B diffusion. B-doped glass is used as a diffusion source. Detection of the diffusion front is through measuring C-V curves for the MOS structure with molybdenum as the metal electrode. The above process is used to fabricate low threshold enhancement mode and depletion mode p-channel MOSFET's in one diffusion step.