A Temperature Tracking Read Reference Current and Write Voltage Generator for Multi-Level Phase Change Memories

This paper gives a write voltage and read reference current generator considering temperature characteristics for multi-level Ge2Sb2Te5-based phase change memories. Since the optimum SET and RESET voltages linearly changes by the temperature, the voltage supply circuit must track this characteristic. In addition, the measurement results show that the read current depends on both read temperature and the write temperature and has exponential dependence on the read temperature. Thus, the binning technique is applied for each read and write temperature regions. The proposed variable TC generator can achieve below +/- 0.5 LSB precision from the measured differential non-linearity and integral non-linearity. As a result, the temperature characteristics of both the linear write voltage and the exponential read current can be tracked with the proposed variation tolerant linear temperature coefficient current generator.