3-D Memristor Crossbars for Analog and Neuromorphic Computing Applications

We report a monolithically integrated 3-D metal-oxide memristor crossbar circuit suitable for analog, and in particular, neuromorphic computing applications. The demonstrated crossbar is based on Pt/Al 2 O 3 /TiO 2-x /TiN/Pt memristors and consists of a stack of two passive 10 × 10 crossbars with shared middle electrodes. The fabrication process has a low, less than 175°C, temperature budget and includes a planarization step performed before the deposition of the second crossbar layer. These features greatly improve yield and uniformity of the crosspoint devices and allows for utilizing such a fabrication process for integration with CMOS circuits as well as for stacking of multiple crossbar layers. Furthermore, the integrated crosspoint memristors are optimized for analog computing applications allowing successful forming and switching of all 200 devices in the demonstrated crossbar circuit, and, most importantly, precise tuning of the devices' conductance values within the dynamic range of operation. We believe that the demonstrated work is an important milestone toward the implementation of analog artificial neural networks, specifically, those based on 3-D CMOL circuits.