Firing of a Pulse and its Control Using a Novel Floating Electrode Bi-Resistive Device
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Firing of a Pulse and its Control Using a Novel Floating Electrode Bi-Resistive Device Y. Kang, M. Verma, T. Liu, M. Orlowski Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA ABSTRACT A novel resistive device with a floating electrode (RFED) has been manufactured as a stack of layers Cu/TaOx/Pt/TaOx/Cu in a crossbar array comprising two single resistive switches merged antiserially at the common inert Pt floating electrode. The device exhibits four states HRS/HRS, HRS/LRS, LRS/HRS and LRS/LRS, where HRS and LRS are the high and low resistance states, respectively, with only LRS/LRS being fully conductive. When the voltage on one Cu electrode is increased to a value Vth-on(A), a conductive nanofilament (CF) in switch A is formed, while suppressing CF formation in switch B. When the voltage is then extended to negative bias, a sudden jump in the I-V characteristics is observed at Vth-on(B), when the 2nd CF in switch B is formed rendering the RFED device fully conductive. If the current surge just after the formation of CF in 2nd switch exceeds the reset current of the 1st CF, the 1st CF ruptures shortly thereafter, i.e. the conductive state is destroyed as soon as it has been created. This property proves valuable for applications in neural networks where a generation of a current pulse at a critical threshold is required. The height and the time width of the firing pulse is an inherent property of the device and can be controlled by the parameters of the individual switches and their set/reset operations. INTRODUCTION Solid electrolyte materials using ionic transport between an oxidizable anode and inert cathode are amongthe most promising candidates to replace the conventional floating-gate device based non-volatlite memory beyond the 11 nm technology node [1-3]. A single Cu/TaOx/Pt switch relies on electrochemical deposition and rupture of a conductive filament (CF) of the active Cu electrode [4]. The manufacturing of the RFED device that comprises two single individual resistive switches merged at the common inert Pt electrode is described in the companion paper to this conference [5]. The drawback of single resistive device in a cross point architecture is the so-called sneak path problem [6], where the state of conductivity of a selected cell can be compromised by currents through other cells in ON states connected ultimately to the selected column and row. The sneak path issue can be solved by the RFED device as described in [7] along with operation of RFED. The device can be manufactured still in a cross point array of 4F2 size (F being the minimum feature size) as depicted in Fig. 1a. A typical pulse firing of the RFED device is shown in Fig.1b. DEVICE CHARACTERISTICS
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The concept of RFED operation is shown in Fig. 2a and is described now in more detail. When the voltage is first (1) increased from 0V on the positive axis, a value Vth-on(A) will be reached at which the CF in switch A will be formed. Because the switc
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