Materials selection and fabrication nanotechnology of the composite memristor-diode crossbar — the basis of neuroprocessor hardware implementation

Abstract

To examine the operation of the memory and logic matrices of the neuroprocessor, it is necessary to produce a laboratory composite memristor-diode crossbar, which is the basis of these matrices. For this purpose, the authors of this article have chosen materials and fabrication nanotechnology of Zener diode semiconductor layers and a memristor layer that provide optimal characteristics of the diode and memristors. This article shows that magnetron-sputtering method is optimal for fabrication of both diodes and memristors. Thus, all of composite memristor-diode crossbar layers, including conducting paths, can be fabricated in single technological module. ZnOx was chosen as the n-type semiconductor, the carrier concentration in which is controlled by changing the stoichiometry of the compound during reactive magnetron sputtering. The second p-type layer of the diode was obtained by magnetron sputtering of a silicon target doped with boron. The results show that for the p-Si/ZnOx heterojunction, there is an optimal molar fraction of zinc, which provides the best characteristics of the diode, and an increase in the doping level of the p-Si layer leads to an increase in the nonlinearity of the current-voltage characteristic and a decrease in the voltage of the reversible breakdown. The greatest stability of electrical parameters — switching voltages and resistances in high-conductive and low-conductive states — was achieved in a memristor with doped titanium oxide W/TixAl1-xOy/TiN, which is due not only to the choice of mixed oxide, but also to the choice of its fabrication technology. The measured current-voltage characteristics of separate cells prove the operability of fabricated memristor-diode crossbar. The authors show that the high resistance of the closed diode leads to the almost complete disappearance of the reverse branch of the memristor current — voltage characteristic, since the small resistance of the memristor is lost against the background high resistance of the diode. The developed unified nanotechnology for fabricating a combined memristor-diode crossbar allows the production of ultra-large memory and logic matrices of a neuroprocessor based on one technological module with reactive magnetron sputtering.