Design Of Memory Cell Structure And Drive Circuits Of Chalcogenide-Based Phase-Change RAM

This dissertation focuses on the study of three aspects, including the novel CRAM cell structure which can decrease the write current and simplify the fabrication process, the circuit model of memory cell which reflects the switch phenomenon of the resistance of CRAM cell, and integrated CRAM drive circuits which can store and read the data.The I-shaped figure memory cell which is composed of "phase change layer + heater layer + phase change layer" is proposed according to the thermal compatibility between memory cell and the periphery circuits for the first time. The heater layer which has smaller size than phase change layer heats the phase change layers with two terminals simultaneously. On the one hand, it is observed that the reset current of cell is decreased according to the temperature distribution simulation of the memory cell with this structure during the phase change induced by the heating current. On the other hand, with this structure, the transistor can stand the temperature which conducts from cell when the material changes its phase under the high temperature. So, the thermal compatibility between memory cell and the periphery circuits is achieved.For the circuit model of memory cell, two resistances are selected to represent the two storage states under the control of data signals. This method achieves the anticipated switch of resistance of circuit model under the write signals. The memory cell circuit model is provided to the design of drive circuits. And this model is utilized to design the drive circuits of this dissertation for checking the rationality of read circuit of CRAM.The structure of drive circuits is achieved integrally starting from interface of external signals. Drive circuits are composed of control signal model, pulse width selection model, write/read control model, decoder and memory array model and so on. In the design, internal structure of every model is studied according to the difference function of respective model. Then the principle structure and the function description of every model are studied and researched, and each model is connected successfully and logically.In the design of drive circuits, the read circuit with the structure of transmission gates is designed creatively. This circuit can not only be connected with other models of CRAM drive circuits correctly, but also can restrain the transmission of the potential read data during writing data to avoid the data disturbance.In conclusion, the studies of this dissertation reach the anticipate targets with some innovation and integrity, to impel CRAM to develop toward the product.