The surface and materials science of tin oxide

Thin-film transistors (TFTs) are the fundamental building blocks for the rapidly growing field of macroelectronics. The use of plastic substrates is also increasing in importance owing to their light weight, flexibility, shock resistance and low cost. Current polycrystalline-Si TFT technology is difficult to implement on plastics because of the high process temperatures required. Amorphous-Si and organic semiconductor TFTs, which can be processed at lower temperatures, but are limited by poor carrier mobility. As a result, applications that require even modest computation, control or communication functions on plastics cannot be addressed by existing TFT technology. Alternative semiconductor materials that could form TFTs with performance comparable to or better than polycrystalline or single-crystal Si, and which can be processed at low temperatures over large-area plastic substrates, should not only improve the existing technologies, but also enable new applications in flexible, wearable and disposable electronics. Here we report the fabrication of TFTs using oriented Si nanowire thin films or CdS nanoribbons as semiconducting channels. We show that high-performance TFTs can be produced on various substrates, including plastics, using a low-temperature assembly process. Our approach is general to a broad range of materials including high-mobility materials (such as InAs or InP).

High-performance thin-film transistors using semiconductor nanowires and nanoribbons

CdSe thin film transistor (TFT) structures which have been ion implanted with 50 keV 52Cr, 50 keV 27Al, or 15 keV 11B have a very steeply rising conductivity above some threshold dose and exhibit modulated transistor characteristics over certain ranges of implant dose, even though there is no thermal annealing during or after ion implantation. These results are interpreted using a model based on grain boundary trapping theory. The dependence of leakage current on implant dose, and of drain current (at a fixed dose) on gate voltage are described very well by this model, when the drain voltage is very small. Using this simple model, the important parameters of the polycrystalline CdSe film, namely the trap density per unit area in the grain boundary, the donor density, grain size, and electron mobility can be deduced. The effect of thermal annealing on implanted and unimplanted CdSe TFT’s has also been studied and the model appears to give a general description of the conductivity behavior in polycrystallin...

Conductivity behavior in polycrystalline semiconductor thin film transistors

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high-k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum...

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics

The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composite using in conductometric gas sensors and can restrict application of nanocomposites in these devices. Technology features of composite synthesis and device fabrication, which should be taken into account while designing and fabricating sensors based on metal oxide composites, are considered. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

Metal oxide composites in conductometric gas sensors: Achievements and challenges

We have successfully made thin film transistors on transparent, flexible polymer substrates. These transistors have electrical properties suitable for driving the pixels in active matrix liquid crystal displays and also for building integrated row driver circuits. The devices are fabricated on polyethylene naphthalate using a low temperature CdSe process at a maximum temperature of 150°C, by evaporation and radio frequency sputtering onto unheated substrates, with pattern definition using standard photolithography and etching. Electrical properties achieved include carrier field effect mobilities of >30 cm 2 /V s, threshold voltages of ∼2 V, switching ratio >10 6 , an off-state leakage current of −12 A and an on-state drive current of >1 μA with a gate voltage swing of

Thin film transistors for displays on plastic substrates

An investigation of doping of SnO2 by ion implantation and application of ion-implanted films as gas sensors

The effects of Sb implantation into textured thin films of SnO2 prepared by RF sputtering have been characterised by a range of techniques including secondary ion mass spectrometry (SIMS), X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), infrared reflectance, X-ray diffraction and conductivity measurements. The depth distribution of implanted 121Sb ions at low dose is characterised by a truncated bell-shaped distribution, with mean implantation ranges of 250 A for 90 keV implantation and 370 A for 150 keV implantation. However, owing to surface sputtering, the maximum in the implantation profile shifts toward the surface with increasing ion dose and for 90 keV ions at doses above 3 × 1016 cm–2, the implantation profile is sputter limited with maximum implant concentration at the surface. Electrical activation of the implanted ions is achieved at temperatures lower than those required to cause complete sintering of the small grains of the as-deposited films. The surface concentration of Sb seen in XPS increases during post-annealing treatments for Sb doses up to 3 × 10l5cm–2, but decreases at the higher dose of 3 × 1016 cm –2. These observations are discussed in terms of Sb segregation and Sb4O6 evaporation during the post-annealing treatment. The effects of Sb in introducing carriers into the surface region are investigated both by conductivity measurements and by UPS. The latter technique reveals directly occupation of Sn 5s conduction band states. Sb-implanted SnO2 thin films can be used as sensors for detection of methane at much lower temperatures than is possible with undoped films.

n-Type doping of SnO2 thin films by Sb ion implantation

A novel poly-Si correlated double sampling circuit, which can be used as a noise and offset cancellation block in large area X-ray sensor readout electronics is presented. The circuit is simple, robust to threshold voltage variations and its topology provides high speed and low power consumption.

A novel correlated double sampling poly-Si circuit for readout systems in large area X-ray sensors

A study of the noise performance of gate overlapped polycrystalline silicon thin-film transistors (TFTs) is presented. Low-frequency noise measurements were carried out on n- and p-type samples fabricated by excimer laser crystallization. It is shown that the carrier number fluctuation model applies not only to n-type but also to p-type devices. The density of oxide traps was extracted from the noise measurements and was of the order of 10/sup 18/-10/sup 19/ eV/sup -1/ cm/sup -3/.

M.J. Lee

Papers

Thin film transistors for displays on plastic substrates

An investigation of doping of SnO2 by ion implantation and application of ion-implanted films as gas sensors

n-Type doping of SnO2 thin films by Sb ion implantation

A novel correlated double sampling poly-Si circuit for readout systems in large area X-ray sensors

Flicker noise in gate overlapped polycrystalline silicon thin-film transistors