P.G. LeComber

Application of amorphous silicon field effect transistors in addressable liquid crystal display panels

It is shown that thin-film field effect transistors (FETs) made from amorphous (a-) silicon deposited by the glow-discharge technique have considerable potential as switching elements in addressable liquid crystal display panels. The fabrication of the elements and their characteristics with steady and pulsed applied potentials are discussed in some detail. Two important points are stressed: (i) a-Si device arrays can be produced by well-established photolithographic techniques, and (ii) satisfactory operation at applied voltages below 15VV is possible. Small experimental 7×5 transistor panels have been investigated and it is shown that with the present design up to 250-way multiplexing could be achieved. The reproducibility of FET characteristics is good and in tests so far no change has been observed after more than 109 switching operations.

The switching mechanism in amorphous silicon junctions

Abstract Extensive new results have been obtained on memory switching in a-Si p + ni junctions. It is shown that the ON-state has its origins in a highly conducting filament less than lμm in diameter. The physical mechanisms that could play a role in the switching operations are discussed.

Solid phase crystallization of thin films of Si prepared by plasma‐enhanced chemical vapor deposition

Solid phase crystallization of thin films of undoped amorphous Si prepared by plasma enhanced chemical vapor deposition has been studied by transmission electron microscopy (TEM). From the TEM images, the thermodynamic parameters for the amorphous and crystalline phases were extracted. These parameters were compared with those previously reported for evaporated, chemical vapor deposited, and self‐implanted amorphous Si. We conclude that the thermodynamic parameters are very similar for different amorphous Si films, although the initial structure of the films is comparatively different from one to another. To explain this, the existence of an intermediate amorphous state is assumed and discussed.

The characteristics and properties of optimised amorphous silicon field effect transistors

A series of experiments aimed at improving the performance of amorphous silicon field effect transistors has been carried out. The dc and dynamic characteristics of the optimised devices are described. Stable devices capable of ON-currents of the order of 100 μA with OFF-currents ≃10−11 A can be fabricated which could, in principle, be used to address more than 1000 lines of a liquid crystal display. The properties of the highly conducting ON-state channel have also been studied. The field effect mobility, 0.3 cm2 V−1 s−1 at room temperature, has an activation energy of 0.1 eV at the higher gate voltages. The possible reasons for the improvement in performance over earlier devices are discussed.

Aspects of Non-Volatility in a-Si:H Memory Devices

ABSTRACT.: a-Si:H p + -n-i devices, after a once only forming process, switch between two distinct states, both of which are memory states, and are electrically programmable with pulses in the nanosecond range with at least a 1 million cycle endurance. They are known to be non-volatile memory states which persist for long periods. This paper examines the nature of this non-volatility by looking at the effects of time, temperature, bias and radiation. It is found that these digital memory states persist with no change in state for at least four years under zero bias, and that they can withstand high temperatures both under bias and at zero bias. This and a resistance to radiation and a space environment shows that a mechanism of charge storage is unlikely and that they may have applications in hostile environments. The reason for such stability is unclear, but may be associated with the incorporation and distribution of metal in the filamentary region.

Some new results on transport and density of state distribution in glow discharge microcrystalline silicon

Abstract The electronic properties of the material are discussed on the basis of the grain boundary trapping model proposed for polycrystalline Si. In spite of the difference in crystallite sizes it is shown that the model is applicable, leading to 1011 cm−2 filled states between crystallites. Gap state densities between 2 × 1018 and 4 × 1018cm−3eV−1 are deduced from field effect measurements.

Analogue memory effects in metal/a-Si:H/Metal memory devices

In this paper we present experimental data for Metal/a-Si:H/Metal structures which demonstrate that they can be programmed into a range of non-volatile resistance states between 1 kΩ and 1 MΩ with nanosecond pulses of less than 5 V magnitude. A number of results are presented which show the importance of the top metal in the device operation.

Transport in the electron tail states of amorphous silicon

Abstract Fast, time-resolved techniques have been used to investigate the transport of excess electrons in the tail states of a-Si and the interaction of electrons with these states. In the first part new results on low temperature hopping transport are presented and discussed. The second part of the paper deals with the role of electron tail states in compensated a-Si.

Exploratory observations of random telegraphic signals and noise in homogeneous hydrogenated amorphous silicon

Noise measurements on unhydrogenated and hydrogenated rf sputtered intrinsic amorphous silicon reported by D’Amico, Fortunato, and Van Vliet [Solid‐State Electron. 28, 837 (1985)] have 1/f  and Lorentzian spectra, respectively. Similar noise measurements on glow‐discharge deposited hydrogenated amorphous intrinsic silicon reported by Bathaei and Anderson [Philos. Mag. B 55, 87 (1987)] gave a 1/f m spectrum with 0.7<m<1. Even more recently Ley and Arce [Proc. MRS Symposium, San Diego (1989)] have reported random telegraph signals in a‐Si: H/a‐Si1−xNx: H double barrier structures. The associated noise was a Lorentzian noise spectrum. In this paper the first observation of random telegraph signals in notionally homogeneous heavily doped (p+) glow‐discharged‐deposited amorphous silicon is reported. It was found that the current passing through the sample fluctuates between two easily identifiable levels with the periods of fluctuations separated by a quiescent period. The occurrence of these fluctuations is u...

Electrical, optical and luminescence properties of a-Si/SiN multilayers

Abstract Conductivity, absorption and photoluminescence measurements have been carried out on the above structures. The problem of interpreting the results in terms of quantum well effects will be discussed.