Study of amorphous Cu–Te–Si thin films showing high thermal stability for application as a cation supply layer in conductive bridge random access memory devices

Abstract

In this work we demonstrate a thermally stable copper supply layer by Si alloying of Cu_0.6Te_0.4 for application in Conductive Bridge Random Access Memory (CBRAM) cells. A good thermal stability of the copper supply layer is necessary to allow its implementation in future memory devices. In situ X-ray diffraction is used to investigate the crystallization behaviour of Cu_0.6Te_0.4 layers with Si contents up to 20 at%. Low Si concentrations result in crystallization, phase separation and transformations at temperatures below 400 °C, whereas addition of 20 at% Si results in a layer that remains amorphous up to temperatures exceeding 500 °C, making it compatible with back end of line temperatures. Moreover, atomic force microscopy measurements show a very smooth surface morphology up to temperatures exceeding 400 °C. The absence of grain boundaries in the amorphous layer is expected to contribute to the uniformity of the supply layer, and hence it should be beneficial for integration in scaled devices. We attribute the good ability of Si to keep the material amorphous to the high coordination number of Si and the formation of strong bonds which are difficult to break, making rearrangement in a lattice more difficult to proceed. This is further evidenced by XPS measurements, which suggest the occurrence of both Si–Si and Si–Te bonds. CBRAM functionality of this composition is demonstrated by integrating the material in 580 μm diameter dot Pt/Cu–Te–Si/Al₂O₃/n⁺ Si CBRAM cells.