The switching properties of a Programmable Metallization Cell (PMC) structure based on the Ag-As2S3 solid electrolyte were investigated. It was found that at 120 mV of forward bias voltage the device switches from an off state resistance to an on resistance state which is more than two orders of magnitude lower. To bring the structure back in an off state, a reverse bias of several volts is required. The frequency dependence of the switching threshold was carried out. Also is found that time required to switch the structure in a stabile on state is less than 10 μsec and around 60 μsec of reverse bias is required to put the structure back in an off state. The threshold voltage is shown to be nearly independent on temperature, but a linear increase of the on state resistance is observed within 20-80 oC. The results are interpreted in terms of an electronic – superionic transition in chalcogenide glassy semiconductors due to a high concentration of dissolved metal. Keywords: Chalcogenides, Memory switching, Solid electrolytes, Ag-As2S3, Programmable metallization cell
1. Introduction
The Programmable Metallization Cells belongs to structures, which are often used in electronic systems to store information in form of binary data. Their principle of operation is based on electrochemical control of quantity of metal in a thin film of solid electrolyte. Key attributes are low voltage and current operation, rapid write and erase, good retention and endurance, the ability for the storage cells to be physically scaled to a few tens of nm, and a simple fabrication sequence. The memory elements consist from an electrochemically indifferent cathode, a solid electrolyte layer and a source of oxidizable metal atoms which can also act as anode. The solid electrolyte is usually manufactured by dissolving in chalcogenide glassy semiconductors metals, such silver or copper, via thermal or/and photo-dissolution. A review of basic electrochemistry that enables PMC memory operation is reported in [1]. The mostly investigated materials for solid electrolyte are silver doped Ge–S and Ge–Se ternaries [2-5], as well as germanium telluride glasses doped with Cu or Ag [6,7]. However, the As–S chalcogenide glasses were not studied thoroughly yet. The purpose of present work is to investigate the switching properties of a PMC structure based on the Ag-As2S3 as a solid electrolyte manufactured by an analogue technique. The Au–Agx(As2S3)1-x–Ag structures are characterized with electrical properties of current-voltage, switch time, and the evolution of I–V characteristics with frequency and temperature.
2. Experimental
To manufacture PMC structures, the thin films of solid electrolyte have been prepared by vacuum evaporation of glassy arsenic trisulphide from a crucible onto Pyrex glass substrate with a priory deposited gold cathode. The upper electrode i.e. the anode was manufactured from pure silver using the same method of deposition. The transformation of chalcogenide glassy material into a solid electrolyte was performed by dissolution of silver in it, through the light and thermal induced doping.
The switching and memory properties of structures have been studied in the quasi-static electrical conditions. The processing of the data was performed with PC and a data acquisition board manufactured by National Instruments Inc. Voltage double-sweeps were carried out starting at maximum reverse bias, sweeping through zero to an appropriate forward voltage, and sweeping back again through zero to the reverse bias starting point. The acquired signal was the voltage drop across a 10 Ohms series resistor. No programming current was used. The same measurement was performed using different delay times between two consecutive data acquisitions. The data saved in a digital format were analyzed and plotted.
The transient characteristics have been measured using a single or trains of squared voltage pulses with different amplitudes and polarities, obtained from a programmable pulse generator PG8021 (AD Electronic GmbH, Germany).
The effect of temperature was studied by placing the memory devices inside of an electrical furnace. A platinum resistance temperature detector Pt-100 close to the sample served as a temperature controller.


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