Technology Implementation And Memory Design On Amorphous Silicon Antifuse

With their low interconnect delays, Anti-fuses are used as interconnects in field programmable gate arrays(FPGA) for high-speed applications. Anti-fuse device is generally a sandwich structure, which consists of an electrode on both top and bottom of the device, and a anti-fuse film in the middle layer. In this paper, we give the MTM structure in which amorphous silicon serves as anti-fuse film, and aluminum electrode as both TE(top electrode) and BE(bottom electrode). With its resistance up to G?, anti-fuse is initially in the off state. After applying a voltage pulse between two electrodes on the anti-fuse device, the intermediate anti-fuse film is permanently breakdown, forming a conductive channel. In this way the anti-fuse device is converted from a high resistance state to a low resistance state. When in the low resistance state, the anti-fuse device has only a few hundred resistance, or less. Due to its low capacitance and low on-state resistance, the amorphous silicon anti-fuse devices can be used as excellent one time programmable high-speed, high-density read only memory storage unit.In this article, the process conditions of amorphous silicon anti-fuse thin films were studied for making amorphous silicon anti-fuse device under available process conditions. Due to the process issue, the amorphous silicon anti-fuse thin film’s the nonuniform and the inconsistency prevent the breakdown voltage and on-resistance from being consistent. In this paper, an experiment was conducted to measure the process of the breakdown of the amorphous silicon anti-fuse thin films, during which the I-V curve is presented to represent the uniformity and consistency of the film. In addition, FTRI analysis and AFM scan was conducted to analyze what different process parameters would impact on the film properties. In this issue, the main process parameters are temperature, gas pressure and RF power and so on, which affecting the deposition film properties when using the PECVD method for the amorphous silicon anti-fuse film. By conducting various of experiments, the best deposition temperature, the gas pressure and RF power and other process parameters are given as below: deposition temperature between 250-300℃, gas pressure of 600 mTorr, RF power of 60 W. In this process parameters, the breakdown characteristics of the amorphous silicon thin film anti-fuse is most desirable, with medium hydrogen content and very fewer defects.After obtaining uniformly amorphous silicon film, the amorphous silicon anti-fuse programmable read only memory function circuit was also designed including: decoder circuit, readout circuit and the programming circuit. Using CSMC 0.5um process, the memory function of the circuit was simulated. Ring gate are used in all NMOS covered in this article to improve the design of the anti- radiation performance of the chip.