A promising route to building Storage Class Memory (SCM) involves 3D stacking of multiple layers of nonvolatile memory crosspoint arrays. In order to realize this vision, the memory element at each crosspoint node must be in series with an access device that can support high current density when selected, low leakage when unselected, and which is also fully compatible with a Back-End-Of-the-Line (BEOL) fabrication process. This talk will provide an overview of our work on novel access devices based on Cu-containing Mixed Ionic Electronic Conduction (MIEC) materials, which not only meet all of the above requirements but also allow bipolar memory operation. We will show some experimental results on prototype MIEC access devices pertaining to studies of their scalability, cycling endurance, integration with Phase Change Memory (PCM), and array fabrication in a CMOS-compatible process.