M.J. Rose

Analogue memory and ballistic electron effects in metal-amorphous silicon structures

Abstract We present experimental results showing that p+ amorphous silicon memory structures exhibit polarity-dependent analogue memory switching. The effect is non-volatile and we propose that it is associated with changes in a tunnelling barrier within the structure. It is also observed that conduction in the memory ON state is restricted to a narrow conducting channel through which the electrons can, under certain conditions, travel ballistically. As a conseauence, auantized resistance levels associated with ballistic electron transport are observed under certain circumstances. In the presence of a magnetic field, additional steps in the auantized resistance levels occur. A particular feature of this auantized resistance is that the effect can be observed at relatively high temperatures (up to about 190 K).

Capacitance anomaly near the metal-non-metal transition in Cr-hydrogenated amorphous Si-V thin-film devices

Abstract We present experimental results that show a metal—non-metal (MNM) transition occurring in hydrogenated amorphous Si (a-Si: H) analogue memory devices as a function of temperature. The dc resistance of the devices undergoes a continuous change in the range 65–100 K from semiconductor-like behaviour to metallic behaviour, as the temperature increases. The ac conductivity, measured over the frequency range 1–3·1 × 107 Hz, shows an anomalous change as the temperature is varied over the MNM transition. Ac characteristics were modelled using multicomponent RC and RL equivalent circuits below and above the MNM transition region respectively. It is found that the capacitance increases markedly when the temperature approaches the MNM transition from the semiconductor side. Near the transition temperature this capacitance disappears, and the equivalent circuit now requires an inductive component together with a resistance which has a positive temperature coefficient of resistance equivalent to that of the ...

Quantization effects in metal/a-Si:H/metal devices

Abstract We present experimental results showing that metal/p+/metal amorphous silicon (a-Si: H) memory structures exhibit room temperature quantized electron transport associated with quantized resistance. The quantization of resistance is observed at values of R = h/2ie2, where i is an integer or a half integer.

DC and ac measurements on metal/a-Si:H/metal room temperature quantised resistance devices

Abstract Direct-current (dc) and alternating-current (ac) conductivities of room temperature electroformed Cr/p + -a-Si:H/V thin film quantised resistance devices have been measured as a function of temperature, applied field and frequency. The quantised resistance does not change over a temperature range. This invariance is in accordance with the theoretical model suggested for high temperature quantised resistance phenomena. The onset of quantised resistance jumps is associated with the formation of an inductive component within the structure indicating a temporary formation of a metallic conduction channel under the effect of an applied electric field.

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.

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.

Analogue Memory Effects in Metal/ a-Si:H /Metal Thin Film Structures

The ac conductivities of non-volatile analogue memory states are measured in electro-formed Cr/p + /V amorphous silicon structures for a broad frequency range (from 0.1 Hz to 32 MHz). The results suggest that the memory action is associated with electronic processes.

An experimental evaluation of transient and modulated photocurrent density-of-states spectroscopies

Abstract An evaluation of transient photocurrent (TPC) and modulated photocurrent (MPC) spectroscopies as a means of studying the density and capture properties of localized states in amorphous semiconductors is presented. Freauency-domain analysis of TPC data via the discrete Fourier transform (TPC FT) permits a direct comparison with MPC data obtained using conventional lock-in techniaues to be made. Results obtained from undoped hydrogenated amorphous silicon over a wide range of temperatures and optical excitations are used to explore the limits of resolution and applicability, and to highlight the relative merits, of each approach. It is shown that TPC spectroscopy offers significant practical advantages over MPC spectroscopy from the viewpoint of signal-to-noise performance. Discrepancies between TPC FT and MPC data obtained from the same sample under equivalent conditions suggest that the Fourier transform pairing of these methods is not exact, even when the reauirements of low excitation are met. Capture coefficients of defect states calculated from the temperature dependence of the TPC data and the optical excitation dependence of the MPC data disagree, having values of 7 × 10−9 and 5 × 10−7 cm3 s−1 respectively. Density-of-states profiles agree well for tail states (measured at low temperatures) but are less satisfactory at deeper energies.

Miniaturized optoelectronic tweezers controlled by GaN micro-pixel light emitting diode arrays.

A novel, miniaturized optoelectronic tweezers (OET) system has been developed using a CMOS-controlled GaN micro-pixelated light emitting diode (LED) array as an integrated micro-light source. The micro-LED array offers spatio-temporal and intensity control of the emission pattern, enabling the creation of reconfigurable virtual electrodes to achieve OET. In order to analyse the mechanism responsible for particle manipulation in this OET system, the average particle velocity, electrical field and forces applied to the particles were characterized and simulated. The capability of this miniaturized OET system for manipulating and trapping multiple particles including polystyrene beads and live cells has been successfully demonstrated.

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...