dc.description.abstract | The development goals of consumer electronics products are multi-function, high performance, long standby time, small and thin. The memories of these products need high density, high read/write speed, low power consumption and long life time. The volatile memories including SRAM and DRAM have been used for long time. Nowadays, the volatile memory was integrated with non-volatile memory in many applications. The volatile memory in some products were even replaced by non-volatile memory to achieve the advantage of low power consumption. The non-volatile memory has many advantages, such as data storage without power supplication, zero standby power, and instant reboot. At present, the main stream non-volatile memory is Flash memory due to its low cost and power consumption. However, the Flash technology still have some issues to limit it development, such as slow write speed (us~ms), poor endurance (105) and higher write voltage ( > 5 Volt). For the request of future consumer products, many famous companies start to research several emerging non-volatile memories, such as phase change memory (PCM), magnetic memory (MRAM), Ferro-electric memory (FERAM) and resistive memory (ReRAM). This thesis focuses on two promising memories including PCM and RRAM.
At first, the introduction of memory technology was addressed. The second is the PCM characteristic. The resistance of PCM is dependent on the crystal structure of the phase change material. When phase change material of PCM device is crystalline, the device is low resistance state (LRS). When phase change material of PCM device is amorphous state, this device is high resistance state (HRS). Because the resistance change of the PCM device is by using joule heat, the device needs to be applied current or voltage to change its resistance state. Hence, two types of write circuit are implemented in peripheral circuit. One is current write circuit and another is voltage write. However, the large number of cells per bit-line has write fail due to the RC delay effect. The RC delay effect will cause the insufficient energy and fail the write operation. In this paper, a path tracking write scheme and circuit has been proposed. With this circuit, the large number cells per bit-line will compensate the energy by the path tracking write circuit to improve the reliability of PCM operation
Next, this thesis proposes the ReRAM technology. The ReRAM device has many outstanding characteristics, including fast switching speed and high temperature reliability. These performances of RRAM are better than those of PCM. The resistance of ReRAM is decided by the connection or rupture of conductive filaments which is composed of oxygen vacancies. However, the over-RESET, which weakens the filament structure, leads to write failure. This paper proposed the write-verify circuit to prevent the over-RESET and improve the reliability.
Finally, the comparison between PCM and ReRAM are discussed. The challenge and future work are also proposed in the last chapter. For the ultra-slim, high performance, and high life time product request, the emerging non-volatile memory will combination the 3DIC technology to achieve these request of future product.
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