Switching and memory effects in amorphous chalcogenide thin films

The performance of threshold- and memory-switching devices is discussed. The threshold devices were prepared by vacuum deposition from the Ge-As-Te-Si system and exhibited threshold voltages over a wide range from less than 2.0 V to greater than 50 V. Lifetimes of the order of 10⁶-10⁸switching operations before failure were obtained and the operation of the threshold device with a capacitative load was demonstrated. Memory-switching devices were prepared from the Ge-As-Te system. The bistable operation is discussed and it is concluded that the bistable impedance states are due to the presence, or absence, of a crystalline filament between the electrodes. Typical pulse levels required to produce the transition between the impedance states were 2 × 10^-2A for 5 × 10^-3s and 5 × 10^-2A for 5 × 10^-6s. The devices possess fairly stable characteristics and currently have lifetimes of 10²- 10³operations before failure; this is expected to improve with device development.