Research On A Novel Antifuse PROM: Design, Fabrication And Radiation Hardening

With the fast development of China's space program, there is an ever increasing demand for radiation hardened integrated circuits. This is coupled with the fact that Western countries are imposing ever stricter export control on radiation hardening techniques and products. Thus, radiation hardening of integrated circuits has become an important research topic on the agenda of China's 11th and 12th Five Year Plans. Radiation hardened antifuse Programmable Read-Only Memory (PROM) is a highly reliable non-volatile memory, and is widely adopted in space electronics as storage medium for program codes and other key data.Development of antifuse PROM in China is in its initial phase, and there are many related issues awaiting in-depth investigation, including: antifuse material, structure, fabrication, breakdown characteristics, eveness, reliability, compatibility of the antifuse fabrication process with the standard Complementary Metal Oxide Semiconductor (CMOS) process, radiation effects and radiation hardening of the antifuse PROM .In this dissertation, in-depth study is conducted centering on various aspects of design and fabrication of radiation hardened antifuse PROM, which include antifuse devices, PROM integrated circuit, radiation effects on the circuit and radiation hardening techniques. Specifically, the contributions of this work are as follows:1. A novel antifuse device structure compatible with the commercial Flash CMOS process is proposed. Antifuse devices based on this structure are designed and fabricated. Experiments are performed on the antifuse devices to characterize their breakdown voltage, breakdown current, breakdown time, and post-breakdown resistance distribution, and the results show that the antifuse devices possesses excellent breakdown characteristics and post-breakdown resistance distribution.2. Based on the proposed antifuse device structure, an 8kbit antifuse PROM is designed and fabricated. Through analysis of the characteristics of the fabricated novel antifuse devices, antifuse memory unit and array and peripheral circuits such as address decoder, programming circuit, and readout circuit are designed. The antifuse PROM chip is fabricated on a commercial Flash CMOS process. Functional tests performed on the antifuse PROM show that it achieves intended programming and readout functions.3. Based on the currently available radiation ground test platforms in China, studies are conducted on the test platforms and methods to characterize the Total Ionization Dose (TID) effect and Single Event Effects (SEEs) of the CMOS ICs. Radiation test plans are developed according to various radiation test platforms. SEEs of a Field Programmable Gate Array (FPGA) caused by the Californium-252 (252Cf) and the HI-13 tandem-accelerator are compared and limitations of the 252Cf source applied to the SEE tests of modern ICs are quantitatively explained.4. Through analyzing the circuit structure of the antifuse PROM, it is shown that the focus of radiation hardening should be targeted toward the TID and Single Event Latchup (SEL) effects. Thus, in this dissertation, TID hardening based on enclosed-gate NMOS design and SEL hardening based on guard-ring are investigated. NMOS transistors with annular or ring gates and various oxide thicknesses are designed and fabricated and their area costs are compared. Approaches of extracting the effective W/L ratios of the transistors are studied and a novel simple approach for extracting the W/L ratio of the ring gate transistor is proposed. The TID effects of transistors with regular gate, annular gate and ring gate of various oxide thicknesses are compared. Radiation hardened antifuse PROM with guard rings are fabricated on a commercial CMOS process, and the area penalty and tolerance to SEL effects is experimentally studied. The study provides experimental data for radiation hardening of CMOS ICs, and is instrumental in choosing the proper hardening strategies and predicting the effect of a particular radiation hardening technique.5. The antifuse PROM is radiation hardened by design and experimentally studied on the radiation effects. Preliminary experimental studies are performed on the TID and SEEs of the proposed antifuse devices and antifuse PROM circuit to characterize the radiation resilience of various parts of the antifuse PROM chip. Experimatal results show that the antifuse device is highly resilient to radiation, while the most radiation-sensitive parts of the chip are the high-voltage device based charge-pump circuit and sense amplifier. Adopting guard-ring can help increase the threshold of Linear Energy Transfer (LET) capable of inducing SEL from 37~52.3Mev·cm2/mg to above 74Mev·cm2/mg. 6. Comparative studies are performed on the radiation effects of Static Random Access Memory (SRAM) based FPGA, Flash memory and antifuse PROM. The TID and SEL radiation tolerances in various CMOS technology nodes are experimentally studied. The Single Event Upset (SEU) effects and the TID functional failure characteristics of various memory units are also compared. The results show that significant difference in SEU and TID effects exists among various memories and provide experimental data for choosing proper memory in space application.