Non-irradiated Devices Research Articles

Characterization of radiation-related damage in bulk-grown silicon–germanium detectors

Electrical properties of irradiated p-type, PIN, Si 1− x Ge x ( x = 0.028 ) devices were compared to the similar non-irradiated devices, which were fabricated on the same wafer. Differences in effective doping concentration, current generation mechanisms and the process activation energies were observed. Effective doping decrease with increasing irradiation fluence was attributed to the acceptor removal process. Material resistivity was measured, for both irradiated and non-irradiated samples, showing radiation-induced increase in material resistivity, which correlated with the acceptor removal hypothesis. Changes in current generation mechanism were attributed to the radiation-induced generation-recombination centers creation. Dominance of the Space Charge Region (SCR) current generation mechanism was assumed and confirmed for both irradiated and non-irradiated devices. The activation energy of the generation process was shown to be near the theoretical mid-gap. Deep level traps were examined using a current Deep Level Transient Spectroscopy (DLTS) technique. A trap level, with activation energy of 0.43 eV, was detected in both irradiated and non-irradiated samples. The irradiated samples exhibited two additional trap levels with activation energies of 0.12 and 0.27 eV, the levels were attributed to corresponding dislocation types. The 0.12 eV level attribution to B I 0 / + trap correlated with the radiation-induced boron removal hypothesis.

Electrical stresses on ultra-thin gate oxide SOI MOSFETs after irradiation

We present the first experimental data about the wear-out of a 0.1 /spl mu/m partially depleted SOI CMOS technology after heavy ion irradiation. We show that accelerated life tests based on high electric fields yield significant differences between irradiated and nonirradiated devices, even though no or only minor changes are visible in the characteristics of the devices after irradiation. First, the time to breakdown of the front gate oxide is significantly lower in the irradiated samples. The fresh devices experienced breakdown after 5-8/spl middot/10/sup 22/ electrons/cm/sup 2/ were injected across the oxide during high field electrical stress. In the irradiated oxide, the breakdown was reached at much lower injected charge values, between 0.5/spl middot/10/sup 22/ electrons/cm/sup 2/ and 1.5-1/spl middot/10/sup 22/ electrons/cm/sup 2/ depending on the ion fluences. This translates into a lifetime reduction of 10%-20% of its initial value. Furthermore, the degradation kinetics of the threshold voltage and transconductance peak are strongly affected by ion strikes. In particular, a sudden shift of the threshold voltage and an acceleration in the degradation of the transconductance peak were observed upon the application of an electrical stress, which have no correspondence in nonirradiated devices. An acceleration in the degradation of the parasitic back transistor was observed as well. These phenomena were interpreted in terms of latent damage left by the irradiation in the oxides that make up SOI devices.

Computer Simulation and AFM Characterization of Standard and Irradiated Si PIN Devices

In this study we present computer simulations and experimental results of electric field distribution inside silicon PIN devices before and after the introduction of radiation-induced damage. The investigated devices were irradiated with 24 GeV/ c protons and characterized using atomic force microscopy based methods. The topic of “type inversion” of irradiated silicon devices is simulated using commercial TCAD software. The results of surface potential difference measured by atomic force microscopy on non-irradiated devices are in good agreement with the simulated results for low interface charge case.

Radiation hardness and charge collection efficiency of lithium irradiated thin silicon diodes

Due to their low depletion voltage, even after high particle fluences, improved tracking precision and momentum resolution, and reduced material budget, thin substrates are one of the possible choices to provide radiation hard detectors for future high energy physics experiments. In the framework of the CERN RD50 Collaboration, we have developed PIN diode detectors on membranes obtained by locally thinning the silicon substrate by means of TMAH etching from the wafer backside. Diodes of different shapes and sizes have been fabricated on 50-/spl mu/m and 100-/spl mu/m thick membranes and tested, showing a low leakage current (of 300 nA/cm/sup 3/) and a very low depletion voltage (in the order of 1 V for the 50 /spl mu/m membrane) before irradiation. Radiation damage tests have been performed with 58 MeV lithium (Li) ions up to the fluence of 10/sup 14/ Li/cm/sup 2/ in order to determine the depletion voltage and leakage current density increase after irradiation. Charge collection efficiency tests carried out with a /spl beta//sup -/ particle source have been performed on both nonirradiated devices and samples irradiated up to 1.8/spl times/10/sup 13/ Li/cm/sup 2/. Results reported here confirm the advantages of thinned diodes with respect to standard 300-/spl mu/m thick devices in terms of low depletion voltage and high charge collection efficiency.

Comparison of bulk and interface generation in silicon PIN detectors

Thermal activation energies of bulk and interface-generated currents for high-resistivity silicon detectors are presented and compared. In non-irradiated devices it is shown that the bulk generation activation energy is strongly dependent on the processing technology, with no significant influence of material resistivity. The activation energies of the interface-generated currents on the other hand are shown to be process, resistivity, and orientation independent. The concentration cross-section products of both bulk and interface-generation centers are shown to be process dependent. Samples with resistivity range of 2–28 kΩ cm and orientations 〈1 1 1〉 and 〈1 0 0〉 were used. The activation energies of the current generating centers of proton-irradiated samples are presented.

Charge collection efficiency studies with irradiated silicon detectors

Abstract Small area (1×1 cm 2 ) microstrip detectors, made with a p+-n diode structure on FZ silicon substrates, both with and without oxygen enrichment, have been irradiated with 24 GeV /c protons to fluences of 1.9, 2.9 and 5.1×10 14 p/cm 2 . Their charge collection properties have been studied using a 106 Ru beta-source with a wide bandwidth current amplifier and compared with those for a non-irradiated device. The integrated charge collected at different times (10, 25, 40 and 80 ns ) has been used to estimate the effect of ballistic deficit. Predictions for the reduction in charge collection efficiency expected at fluences as high as 10 15 cm −2 are presented using a parameterization described in earlier work which also fits this data well.

Effects of gamma-ray irradiation on polycrystalline silicon thin-film transistors

The effects of gamma-ray irradiation on the performance of polycrystalline silicon thin-film transistors are investigated. After irradiation, the threshold voltage of the TFTs is shifted negatively and well-defined kinks are formed in the subthreshold regions of the transfer characteristics, explained by the turn-on of back channel and sidewall leakage current paths. In the non-irradiated device, the leakage current I L is controlled by the reverse biased drain junction, while after irradiation I L is limited by the intrinsic resistance of the polysilicon material itself.

Study of radiation effects in /spl gamma/-ray irradiated power VDMOSFET by DCIV technique

Direct-current current-voltage (DCIV) measurement was used to monitor interface recombination currents in /sup 137/Cs /spl gamma/-ray irradiated commercial power VDMOSFETs. The data are correlated with the subthreshold I-V data and charge-pumping current data, which are obtained after various biased-annealing steps. The DCIV method is found to be a convenient technique in monitoring the radiation effects in power VDMOSFET devices. Various parameters measured with the DCIV technique are discussed in conjunction with the charge-pumping data and the data from the midgap method. A two-dimensional MOS device simulator, MINIMOS, was used to illustrate the DCIV data. The simulation results illustrate well the dependence of the measurable DCIV parameters on various radiation-induced physical parameters such as interface-trap density, fixed oxide charge density, and surface recombination velocity. A biased annealing experiment in nonirradiated virgin devices showed that the second current peak in the double peak structure of the DCIV data may be associated with the slow-frequency (300-6000 Hz) charge-pumping signal.

Strong impact of x-ray radiation associated with electron beam metallization of diamond devices

Electron-beam evaporation of metal contact is commonly used in the fabrication of semiconductor devices. We have observed that device irradiation by x-ray photons, which are generated by electrons striking the metal (titanium or gold) to be evaporated, has a strong impact on the characteristics of diamond devices used for radiation detection. It results in an improvement of the detector charge collection efficiency by a factor of 1.5 with respect to nonirradiated devices (standard thermal evaporation). Thermally stimulated current measurements showed that this effect is related to deep trap filling by free carriers generated in diamond by x-ray photons impinging the device during e-beam evaporation. Trap filling results in an increase of the free carrier drift distance before trapping. Study of contact annealing and the thermal stability of trap filling showed that charge detrapping at temperatures above 200 °C annihilates the observed detector sensitivity improvement.

Long-term evaluation of bone formation by osteogenic protein 1 in the baboon and relative efficacy of bone-derived bone morphogenetic proteins delivered by irradiated xenogeneic collagenous matrices.

To investigate the long-term efficacy of irradiated recombinant human osteogenic protein 1 (hOP-1) in bone regeneration and morphogenesis, hOP-1 was combined with a bovine collagenous matrix carrier (0, 0.1, 0.5, and 2.5 mg hOP-1/g of matrix), sterilized with 2.5 Mrads of y-irradiation, and implanted in 80 calvarial defects in 20 adult baboons (Papio ursinus). The relative efficacy of partially purified bone-derived baboon bone morphogenetic proteins (BMPs), known to contain several osteogenic proteins, was compared with the recombinant hOP-1 device in an additional four baboons. Histology and histomorphometry on serial undecalcified sections prepared from the specimens harvested on day 90 and day 365 showed that gamma-irradiated hOP-1 devices induced regeneration of the calvarial defects by day 90, although with reduced bone area compared with a previous published series of calvarial defects treated with nonirradiated hOP-1 devices. One year after application of the irradiated hOP-1 devices, bone and osteoid volumes and generated bone tissue areas were comparable with nonirradiated hOP-1 specimens. Moreover, 365 days after healing regenerates induced by 0.5 mg and 2.5 mg of irradiated hOP-1 devices showed greater amounts of bone and osteoid volumes when compared with those induced by nonirradiated hOP-1 devices. On day 90, defects treated with 0.1 mg and 0.5 mg of bone-derived baboon BMPs, combined with irradiated matrix, showed significantly less bone compared with defects receiving irradiated devices containing 0.1 mg and 0.5 mg hOP-1; 2.5 mg of partially purified BMPs induced bone and osteoid volumes comparable with the 0.1-mg and 0.5-mg hOP-1 devices. Control specimens of y-irradiated collagenous matrix without hOP-1 displayed a nearly 2-fold reduction in osteoconductive bone repair when compared with nonirradiated controls. These findings suggest that the reduction in bone volume and bone tissue area on day 90 may be caused by a reduced performance of the irradiated collagenous matrix substratum rather than to a reduction in the biological activity of the irradiated recombinant osteogenic protein. This is supported by the results of in vitro and in vivo studies performed to determine the structural integrity of the recovered gamma-irradiated hOP-1 before application in the baboon. Recoveries by high-performance liquid chromatography (HPLC) and sodium dodecyl sulfate/ polyacrylamide gel electrophoresis (SDS/PAGE)/immunoblot analyses indicated that doses of 2.5-3 Mrads of gamma-irradiation did not significantly affect the structural integrity of the recovered hOP-1. Biological activity of the recovered hOP-1 was confirmed in vitro by showing induction of alkaline phosphatase activity in rat osteosarcoma cells (ROS) and in vivo by de novo endochondral bone formation in the subcutaneous space of the rat. These findings in the adult primate indicate that a single application of gamma-irradiated hOP-1 combined with the irradiated xenogeneic bovine collagenous matrix carrier is effective in regenerating and maintaining the architecture of the induced bone at doses of 0.5 mg/g and 2.5 mg/g of carrier matrix.

1.2 kV trench insulated gate bipolar transistors (IGBT's) with ultralow on-resistance

In this letter, we report the full development of 1.2 kV Trench IGBT's with ultralow on-resistance, latch-up free operation and highly superior overall performance when compared to state of the art IGBT's. The minimum forward voltage drop at the standard current density of 100 A/cm/sup 2/ was 1.1 V for nonirradiated devices and 2.1 V for irradiated devices. The maximum controllable current density was in excess of 1000 A/cm/sup 2/.

Influence of damage caused by Kr ions and neutrons on electrical properties of silicon detectors

In this paper, new measurements of physical properties of high-resistivity silicon, used in high-energy detectors, are presented. The obtained data contribute to the understanding of the causes which damage the electronic characteristics of the detection systems under irradiation of neutrons and ionized particles (Kr). The Hall effect coefficient ( R H) and resistivity ( ρ) measurements as a function of temperature ( T), for non-irradiated and irradiated by neutrons and Kr ions, were performed. The measurements of the Hall coefficient and resistivity of non-irradiated samples and irradiated at neutron fluences ( Φ⩽9.9×10 10 n/cm 2) and Kr ( Φ⩽7.5×10 8 Kr/cm 2), have shown that the obtained characteristics, R H( T) and ρ( T), are of the same shape as those known for a silicon single crystal. A slight difference of the slope of ln ρ∼ ln T , for neutron- and a large difference for Kr ion irradiation as compared with that of non-irradiated samples, was observed. On increasing the irradiation to Φ larger than the value indicated above, for neutrons and Kr ions, important changes in the physical properties were observed. The resistivity increases with increasing Φ, up to a value of the same order with intrinsic silicon ( ρ∼10 5 Ω cm), for both neutron and Kr ion irradiation. The values of R H increase with increasing Φ up to a fluence, for which a change of sign, from negative to positive, occurs. The variation of values of R H and ρ as a function of Φ, for neutrons and Kr ions, is similar, but the characteristics R H( Φ) and ρ( Φ), are displaced. Therefore, larger values of Φ are needed in order to obtain the same values of ρ as those for Kr ion irradiation. The dependence on T of electrical parameters of samples, irradiated at Φ⩾9.9×10 10 n/cm 2 (neutrons) and Φ⩾7.5×10 8 Kr/cm 3 (ions), cannot be explained, considering the usual theoretical relations. The results, obtained in these experiments, have shown a change of mechanism of conduction due to the damaged regions, where localized levels are created, which are the main cause of the deviation of the electrical characteristics of the detectors from that of the usual non-irradiated device. These studies enable to explain the changes of the measured electrical properties, of the detectors under irradiation.

Effect of hydrogen annealing on hot-carrier instability of X-Ray irradiated CMOS devices

In the very large scale integration (VLSI) technology, the need for high density and high performance integrated circuit (IC) chip demands advanced processing techniques that often result in the generation of high energy particles and photons. Frequently, the radiation damage are introduced by these energetic particles and photons during device processing. The radiation damage created by x-ray irradiation, which can often occur during metal sputtering process, has been shown to potentially enhance hot-carrier instability if the neutral traps which act as electron or hole traps in the silicon dioxide is not annealed out. In this paper, we investigate the effects of annealing using different hydrogen contents and temperatures on the device characteristics and hot carrier instability of 0.5 μm CMOS devices after 1500 mJ/cm2 synchrotron x-ray irradiation. Three different annealing conditions were employed; 400° C H2, 450° C H2, and 400° C H2 + N2. It is found that for all three different hydrogen anneals the normal characteristics of irradiated CMOS devices can be effectively recovered. The hot-carrier instability of bothp- andn-channel MOSFETs are significantly enhanced after x-ray irradiation due to the creation of neutral traps and positively charged oxide traps. After high H2 (100%) concentration anneals at 450° C, the hot-carrier instability in irradiatedn-channel devices is greatly reduced and comparable to the non-irradiated devices. Although the hot-carrier instability inp-channel devices is also significantly reduced after annealing, the threshold voltage shifts are still enhanced as compared to the devices without exposure to x-ray irradiation during maximum gate current stress. For those non-irradiated, but hydrogen-annealedp-channel devices, the hot-carrier instability was observed to be worse than the non-irradiated device without hydrogen annealing.

X-ray radiation damage and a reliability study on bipolar devices

The radiation damage and reliability of bipolar transistors have been studied using the vacuum ultraviolet storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The bipolar devices under study were exposed to x-ray radiation in the range of 1–2 keV. The device parameters were measured before and after irradiation, and were measured again after the devices were annealed. Finally, the devices underwent a reliability test. The study shows that x-ray radiation degrades the common emitter current gain. Upon annealing, the current gain recovers its initial value. Furthermore, the current gain exhibits the same degree of reliability as observed on nonirradiated devices.

HOT CARRIER SENSITIVITY OF MOSFET's EXPOSED TO SYNCHROTRON-LIGHT

The influence of synchrotron-light irradiation for p- and n-chaannel MOSFET's on their sensitivity to hot carrier degradation was investigated. The radiation induces additional interface states and a positive oxide charge. Annealing at 450°C reduces the interface state density to its initial value but not the oxide charge. A hot carrier stress can compensate this remaining charge by trapping electrons. This effect produces an enhanced shift of the threshold voltage compared to non-irradiated devices. After compensating all of the charge due to the irradiation the devices have a degradation behavior comparable to the non irradiated ones.

Radiation Effects in LDD MOS Devices

The purpose of this work is to investigate the response of lightly doped drain (LDD) n-channel transistors to ionizing radiation. Transistors were fabricated with conventional (non-LDD) and lightly doped drain (LDD) structures using both standard (non-hardened) and radiation hardened gate oxides. Characterization of the transistors began with a correlation of the total-dose effects due to 10 keV x-rays and Co-60 gamma rays. We find that for the gate oxides and transistor structures investigated in this work, 10 keV x-rays produce more fixed-charge build-up in the gate oxide, and more interface charge than do Co-60 gamma rays. We have determined that the radiation response of LDD transistors is similar to that of conventional (non-LDD) transistors. In addition, both standard and radiation-hardened transistors subjected to hot carrier stress before irradiation show a similar radiation response. After exposure to 1.0 × 106 rads(Si), non-hardened transistors show increased susceptibility to hot-carrier degradation, while the radiation-hardened transistors exhibit similar hot-carrier degradation to non-irradiated devices. We have demonstrated a fully-integrated radiation hardened process that is solid to 1.0 × 106 rads(Si), and shows promise for achieving 1.0 × 107 rad(Si) total-dose capability.