Electrically addressable tungsten doped phase change device in a through pixel configuration

Abstract

In this paper, we propose and demonstrate electrical switching of a 4% tungsten-doped Ge2Sb2Te5 (W-GST) pixel in a lateral configuration without the need for an auxiliary resistive heater. The phase transition between an amorphous and poly-crystalline state is achieved by Joule heating directly through the 4 μm × 4 μm × 350 nm active volume of the chalcogenide phase change pixel. While undoped GST would be challenging to switch in a lateral configuration due to very large resistance in the amorphous state, W-GST allows for switching at reasonable voltage levels. The pixel temperature profile is simulated using finite element analysis methods to identify the pulse parameters required for a successful electrical actuation. Experimentally, a 1550 nm light source is used for in-situ optical reflection measurements in order to verify the crystallization and re-amorphization of the pixel. As a result of the W doping, we identify volatile and non-volatile regimes with respect to bias voltage and pulse width during crystallization. During amorphization, we observe irreversible material failure after one complete cycle using in-situ optical monitoring, which can be attributed to a migration or segregation process. These results provide a promising path toward electrically addressed devices that are suitable for optical applications requiring amplitude modulation in a reflective geometry, such as spatial light modulators.