Research And Realization Of Novel Antifuse Devices And Total Ionizing Dose Radiation Tolerant Proms

The antifuse devices and antifuse chips have been applied in a lot of fieldsdemanding superior reliability due to their high reliability and high radiation tolerance,such as strategic weapon, satellite communication, and aeronautics and space. Therequirement of antifuse devices and antifuse chips is urgent for China; however, thedevelopment of antifuse technologies in China is just beginning, and a great number ofkey technical problems are eager to be solved. Based on the above background, a largenumber of research work has been done in this dissertation aimed at novel antifusedevices and novel total ionizing dose radiation hardened PROMs. The main research isshown as follows:First, a novel antifuse structure based on bismuth zinc niobate (BZN) high-Kmaterials was proposed, and the preparation technique for the BZN antifuses wasstudied. The structure of the BZN antifuse was Ti/Pt/BZN/Al. The SF6/Ar high densityinductively coupled plasma (ICP) and CF4/Ar high density inductively coupled plasmawere used for etching of the BZN thin films. It was found that the etching mechanism ofthe BZN thin films based on SF6/Ar inductively coupled plasmas and CF4/Arinductively coupled plasmas was ion assisted chemical etching. The optimum etchingparameters of the BZN thin films were obtained, which were3/2for process gas flowratio,25sccm for total gas flow,10mTorr for process pressure, and800W for ICPpower. Under optimum etching conditions, the maximum etch rate of the BZN thinfilms in SF6/Ar plasmas and CF4/Ar plasmas was about43.15nm/min and26.04nm/min, respectively. The surface morphology of the BZN thin films etched in SF6/Arplasmas was smooth, clean, no post-etch residues, and hardly changed in shape;however, some carbon polymers were remained on the surface of the BZN thin filmsetched in CF4/Ar plasmas. Compared to the CF4/Ar inductively coupled plasmas, theSF6/Ar inductively coupled plasmas were desirable for etching of the BZN thin films.The BZN antifuse samples were prepared in circular shape with varied diametersranging from20μm to200μm. The cubic pyrochlore BZN (cp-BZN) antifuse samplesand amorphous BZN (a-BZN) antifuse samples were formed through changing the deposition temperatures of the BZN thin films.Second, the characteristics of the BZN antifuses were investigated includingOFF-state property, programming property, ON-state property, and reliability. Both upto down programming directions and down to up programming directions wereobserved for rupturing the BZN antifuses, and it was found that the programmingdirection of up to down was desirable to program the BZN antifuses. The breakdownvoltages of the cp-BZN antifuse and a-BZN antifuse were approximately4.6V and6.56V, respectively. The OFF-state resistance of either the cp-BZN antifuse or the a-BZNantifuse was on the order of G. The programming voltage, current, and time for thecp-BZN antifuse were5.5V,1.06mA, and2.0ms, respectively. Furthermore, theprogramming voltage, current, and time for the a-BZN antifuse were7.5V,1mA, and0.46ms, respectively. The ON-state resistance for the cp-BZN antifuse and a-BZNantifuse was about17.5and26.1, respectively. Compared to the cp-BZN antifuse,the a-BZN antifuse exhibited higher programming voltages and higher ON-stateresistances; while, the leakage current, programming time, and programming energy forthe a-BZN antifuses were lower. In addition, compared to the gate oxide antifuse, eitherthe cp-BZN antifuse or the a-BZN antifuse showed better programming properties andON-state properties. It was shown that the reliability of the BZN antifuse was high. Thelifetime of the BZN antifuse was well more than10years. When the programmed BZNantifuses subjected to high stress currents, no switch-OFF phenomena were illustrated.The temperature dependence of the ON-state resistance of the BZN antifuses was low.In brief, the characteristics of the BZN antifuses were very excellent, indicating that theBZN antifuse was a novel alternative antifuse structure to replace the gate oxideantifuse.Third, a novel total ionizing dose radiation tolerant device structure was proposed.It was double gate transistor. On one hand, the double gate transistor could withstandhigh voltages; on the other hand, the double gate transistor exhibited an excellent totalionizing dose radiation tolerance. In0.35μm CMOS process, the total dose wasapproximately3Mrad(Si) for the threshold voltage of the double gate transistordecreasing to0V; nevertheless, the dose was only about70krad(Si) for the thresholdvoltage of the high voltage NMOS transistor decreasing to0V, where the voltagewithstanding capability of the high voltage NMOS transistor and the double gate transistor was the same. It was indicated that, compared to the high voltage NMOStransistors, the radiation tolerance of the double gate transistors was improved by43times; while, the voltage withstanding capability was not changed.Fourth, the total dose radiation tolerant double gate antifuse PROM circuit basedon double gate transistors was designed and simulated using0.18μm CMOS process.An improved double gate transistor structure was proposed to satisfy the requirement ofdesigning. The readout threshold of the double gate antifuse PROM constructed byimproved double gate transistors was about110K, which was about22times largerthan the ON-state resistance of the antifuse embedded in the PROM. The traditionalantifuse PROMs including straight gate antifuse PROM and ring gate antifuse PROMwere designed to compare with the double gate antifuse PROM. It was found that theoperating voltages of the traditional antifuse PROMs were3.3V; while, the operatingvoltage for the double gate antifuse PROM was only1.5V.Fifth, the layouts of the straight gate antifuse PROM, ring gate antifuse PROM,and double gate antifuse PROM were designed and fabricated by0.18μm CMOSprocess. The basic function testing showed that the antifuse PROMs mentioned aboveexhibited good programming functions and readout functions. The properties of the totalionizing dose radiation tolerance of the three antifuse PROMs were carried out througha60Co gamma source. It was shown that the total dose radiation tolerance of the straightgate antifuse PROM and ring gate antifuse PROM was about60and600krad(Si),respectively; while, the total dose radiation tolerance for the double gate antifuse PROMwas greater than9Mrad(Si). The total dose radiation tolerance for the double gateantifuse PROM was increased by at least15times compared to the ring gate antifusePROM. In conclusion, compared to the traditional antifuse PROM, the double gateantifuse PROM not only illustrated lower power consumption but also demonstratedhigher total dose radiation tolerance, whereas, the voltage withstanding capability of thedouble gate antifuse PROM was not changed.