Amorphous Silicon Analogue Memory Elements
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AMORPHOUS SILICON ANALOGUE MEMORY ELEMENTS *
M.J. ROSE
+
,
J. HAJTO', P.G. LeCOMBER
I.S. OSBORNE"
,
A.J. SNELL+, A.E. OWEN+ and
University of Dundee, Dundee, Scotland, U.K. +University of Edinburgh, Edinburgh, Scotland, U.K.
ABSTRACT Both Cr/p+/V and Cr/p+/Cr devices exhibit fast electrically programmable memory switching with a programmable voltage range, AVs 5 , which depends only on the choice of the top metal. Despite a difference in A Vs, both types of device have very similar electrical properties, but show one major difference in room temperature I-V characteristics, where under certain conditions, discontinuities are observed. INTRODUCTION In a previous paper [1] we reported that metal/p+-a-Si:H/metal (M/p+/M) A structures show a polarity dependent programmable analogue memory effect. range of stable intermediate resistance states is found and the voltage range, A Vs, over which the device is programmable, is determined by the If the configuration is Cr/p+/V, the nature of the top metal contact. voltage range for programming these addressable resistance states A Vs is - 2V. The devices are If Cr/p+/Cr devices are used, AVs is found to be -,0.5V. first formed by a high field pulse and subsequent conduction is by a current filament [2], with metal from the top contact dispersed in the filamentary region. In this paper we report new measurements on Cr/p+/V and Cr/p+/Cr devices showing them to have many similarities and one major difference. Cr/p+/V devices, when programmed to an ON-state and measured at temperatures between 4K and 190K, exhibit I-V characteristics with a quantised step-like structure in the current which is associated with resistance values of R = h/2ie , where i is an integer (h is Planck's suggesting quantum constant and the e elementary electronic charge), These jumps subsequently split to confinement for the electron flow [3]. Further measurements on (i + I) values in the presence of a magnetic field. quantum transport in these devices have been made and we find that there may be evidence for quantised resistance even at room temperature, with the room temperature I-V characteristics showing structure similar to those measured at low temperature. These are implicitly associated with a currentcontrolled negative-differential resistance (CCNDR), the type associated with In contrast, Cr/p /Cr devices do not filaments and threshold type switching. exhibit these step-like characteristics. EXPERIMENTAL METHODS The The devices used in this work were Cr/p+/Cr or Cr/p+/V structures. a-Si:H for these was prepared from the gas phase by the R.F. glow discharge decomposition of SiHl4 with 104 vppm of B2 H 6 at 300'C, to a thickness of Mat. Res. Soc. Symp. Proc. Vol. 219. ©1991 Materials Research Society
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From these layers 10 jum "pore" structures were prepared as described 1000A. previously [3]. Devices were electrically formed by the application to the top contact of 300 ns pulses whose magnitude was gradually inhcreased up 3to 12V, inducing a gradual change in resistance from the initi
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