K Kobayashi

Impact of 20-MeV /spl alpha/-ray irradiation on the V-band performance of AlGaAs pseudomorphic HEMTs

The irradiation damage in Si-planar-doped AlGaAs pseudomorphic HEMTs integrated in 50 GHz monolithic microwave integrated circuits (MMICs) and subjected to 20-MeV /spl alpha/ and /spl gamma/-ray irradiation is studied. Both the static and the high frequency device parameters have been analyzed. It is shown that the drain current and the effective mobility decrease after irradiation, while the threshold voltage shifts in a positive direction. The degradation of the device performance increases for higher fluence. The decrease of the mobility is thought to result from the scattering of channel electrons by the induced lattice defects and also from the decrease of the electron density in the two dimensional electron gas (2DEG) region. Moreover, the noise figure increases with increasing fluence, while the gain decreases. After 150/spl deg/C post-irradiation thermal annealing for 15 min, the noise figure and gain for 1/spl times/10/sup 12/ /spl alpha//cm/sup 2/ recovers by 67 and 19%, respectively.

Degradation and recovery of AlGaAs/GaAs p-HEMT irradiated by high-energy particle

Abstract Results of an extensive study on the irradiation damage and its recovery behavior resulting from thermal annealing in AlGaAs/GaAs pseudomorphic high electron mobility transistors (HEMTs) subjected to a 220-MeV carbon, 1-MeV electrons and 1-MeV fast neutrons are presented. The drain current and effective mobility decrease after irradiation, while the threshold voltage increases in positive direction. The decrease of the drain current and mobility is thought to be due to the scattering of channel electrons with the induced lattice defects and also to the decrease of the electron density in the two dimensional electron gas region. Isochronal thermal annealing shows that the device performance degraded by the irradiation recovers. The decreased drain current for output characteristics recovers by 75% of pre-rad value after 300°C thermal annealing for AlGaAs HEMTs irradiated by carbon particles with a fluence of 1×10 12 cm −2 . The influence of the materials and radiation source on the degradation is also discussed with respect to the nonionizing energy loss. Those are mainly attributed to the difference of particle mass and the probability of nuclear collision for the formation of lattice defect in Si-doped AlGaAs donor layer. A comparison is also made with results obtained on irradiated InGaP/InGaAs p-HEMTs in order to investigate the effect of the constituent atom. The damage coefficient of AlGaAs HEMTs is also about one order greater than that of InGaP HEMTs for the same radiation source. The materials and radiation source dependence of performance degradation is mainly thought to be attributed to the difference of mass and the possibility of nuclear collision for the formation of lattice defects in Si-doped donor layer.

Radiation damage in flash memory cells

Results are presented of a study on the effects of total ionization dose and displacement damage, induced by highenergy electrons, protons and alphas, on the performance degradation of flash memory cells integrated in a microcomputer. A conventional stacked-gate n-channel flash memory cell using a 0.8 lm n-polysilicon gate technology is employed. Irradiations by 1-MeV electrons and 20-MeV protons and alpha particles were done at room temperature. The impact of the fluence on the input characteristics, threshold voltage shift and drain and gate leakage was investigated. The threshold voltage change for proton and alpha irradiations is about three orders of magnitude larger than that for electrons. The performance degradation is mainly caused by the total ionization dose (TID) damage in the tunnel oxide and in the interpoly dielectric layer and by the creation of interface traps at the Si–SiO2 interface. The impact of the irradiation temperature on the device degradation was studied for electrons and gammas, pointing out that irradiation at room temperature is mostly the worst case. Finally, attention is given to the impact of isochronal and isothermal annealing on the recovery of the degradation introduced after room temperature proton and electron irradiation. 2002 Elsevier Science B.V. All rights reserved.

Defect assessment of irradiated STI diodes

The device performance degradation and the induced lattice defects of shallow trench isolation (STI) n þ p diodes, subjected to different high energy particle irradiations will be described. The diodes were irradiated with 1-MeV neutrons, 2-MeV electrons and 20-MeV protons. Insight into the displacement damage mechanisms is obtained by analyzing the relation between the current damage coefficient, and the calculated non-ionizing energy loss. Deep level transient spectroscopy is used to detect the radiation-induced electron capture levels. Some levels are thought to be related to the degradation of the STI interfaces. The degradation of the electrical performance results from the induced defects. A different degradation behavior in dependence of the irradiation particle is found for meander diodes compared with square diodes. 2002 Elsevier Science B.V. All rights reserved.

Radiation effects on the current–voltage and capacitance–voltage characteristics of advanced p–n junction diodes surrounded by shallow trench isolation

Abstract This paper investigates the impact of 20 MeV proton irradiation on the current–voltage ( I – V ) and capacitance-voltage ( C – V ) characteristics of different geometry n + –p-well junction diodes surrounded by shallow trench isolation and processed in a 0.18 μm CMOS technology. From I – V characteristics, a higher current damage coefficient was found for the bulk than for the peripheral component. The radiation-induced boron de-activation resulted in a lowering of the p-well doping, which has been derived from high-frequency C – V measurements. This was confirmed by deep level transient spectroscopy (DLTS) analysis, revealing the presence of interstitial boron related radiation defects. As will be demonstrated for the bulk leakage-current damage coefficient, the electric field enhanced generation rate of charge carriers and the radiation-induced boron de-activation should be accounted for properly.

Effects of high-temperature gamma ray and electron irradiation on npn Si transistors

The degradation of npn Si transistors, subjected to /spl gamma/ and 1-and 2-MeV electrons at different irradiation temperature, is studied. For the 20/spl deg/C irradiation I/sub B/ increases significantly, while I/sub C/ markedly decreases for V/sub BE/ above 0.6 V. The radiation-induced degradation becomes significantly smaller for higher exposure temperatures. For the 200/spl deg/C irradiation, I/sub B/ remains of the same order as before irradiation, while I/sub C/ is nearly identical. It is also noticed that h/sub FE/ for the 200/spl deg/C /spl gamma/-ray irradiation amounts to 82% of the starting value. A broad distribution of hole trapping levels is observed in the base region for the 20/spl deg/C exposure, while an electron trap with energy level Ec - 0.18 eV and a broad DLTS signal around 150 K was found in the collector region. The hole capture levels in the base are related to radiation damage at the Si-SiO/sub 2/ interface region. It is concluded that the radiation-induced defects in the base and collector regions correlate well with the device degradation of the npn Si transistors.

Substrate effects on the degradation of irradiated Si diodes

Irradiation damage in n/sup +/p and p/sup +/n Si diodes by 1-MeV fast neutrons and 1 to 2-MeV electrons is studied as a function of type of Si substrate and radiation source. The degradation of the electrical performance of diodes by irradiation increases with increasing fluence and is much larger for CZ-Si diodes than for FZ-Si diodes. The difference of radiation damage is thought to be due to the formation of lattice defects which are associated with the creation of oxygen related complexes. The degraded performance recovers by thermal annealing. The activation energy of reverse current recovery of n/sup +/p Si diodes irradiated by neutrons with a fluence of 1/spl times/10/sup 13/ n/cm/sup 2/ is calculated to be 0.35 and 0.19 eV.

Radiation effect on n-MOSFETs fabricated in a BiCMOS process

Abstract Results are presented of a study on the radiation damage in n-MOSFETs fabricated in a 0.8 μm single-well BiCMOS process, subjected to 20-MeV protons. A comparison is made with the degradation behavior induced by γ-ray irradiation. Finally, the recovery under post-irradiation thermal annealing is also reported.