Impact Ionization

Using a novel sub-nanosecond pulse current-voltage measurement technique, InGaP/GaAs heterojunction bipolar transistors were shown to survive strong impact ionization and to have a much larger safe operating area than previously measured or predicted. As the result, an empirical model for impact ionization was constructed and added to a commercially available HBT model. The modified model can predict the HBT characteristics across the enlarged safe operating area, including strong avalanche breakdown and flyback. The modified model can be used to simulate not only the ruggedness of high-power amplifiers, but also the performance of ultra-wideband pulse generators.

Part I of this paper dealt with the hot carrier reliability evaluation of Gate Electrode Workfunction Engineered Recessed Channel (GEWE-RC) MOSFET involving channel recession and gate electrode workfunction engineering integration onto the conventional MOSFET, using an ATLAS device simulator. It was demonstrated that with the gate stack architecture incorporated onto the GEWE-RC MOSFET and tuning of various structural design parameters such as gate length (LGLG), negative junction depth (NJD), substrate doping (NANA), gate metal workfunction, substrate bias (VSUBVSUB), drain bias (VDSVDS) and gate oxide permittivity (εox2εox2), excellent hot carrier immunity can be achieved in terms of conduction band offset, reduced electron velocity, electron temperature, hot electron injected gate current and impact ionization substrate current. This paper focuses on the analog and large signal performance metrics in terms of linearity, intermodulation distortion, device efficiency and speed-to-power dissipation design parameters. Moreover, the paper also discusses the effect of gate stack architecture and various design parameters such as LGLG, NJD, NANA, gate metal workfunction and εox2εox2 for different substrate (VSUBVSUB) and drain to source (VDSVDS) voltages. The work, thus, proves the effectiveness of GEWE-RC for RFICs with a higher efficiency, better linearity performance; and designing and modeling of power amplifiers.

Ionization and fragmentation of water and uracil molecules was studied both by electron and proton impact. A special coincidence technique allows on an event by event basis the investigation of product ions formed upon the collision of protons with neutral molecules including the identification of the charge state of the projectile. This enables the characterization of the ionization processes occurring, i.e. direct ionization, single electron capture or double electron capture for 0, 1 or 2 electrons that are transferred from the target to the projectile, respectively. For uracil the fragmentation patterns obtained by electron and proton impact ionization reveal close similarities and indicate a comparable amount of excitation for the two different ionization mechanisms at high enough projectile energies.

Single-molecule Förster resonance energy transfer (smFRET) is a powerful tool for extracting distance information between two fluorophores (a donor and acceptor dye) on a nanometer scale. This method is commonly used to monitor binding interactions or intra- and intermolecular conformations in biomolecules freely diffusing through a focal volume or immobilized on a surface. The diffusing geometry has the advantage to not interfere with the molecules and to give access to fast time scales. However, separating photon bursts from individual molecules requires low sample concentrations. This results in long acquisition time (several minutes to an hour) to obtain sufficient statistics. It also prevents studying dynamic phenomena happening on time scales larger than the burst duration and smaller than the acquisition time. Parallelization of acquisition overcomes this limit by increasing the acquisition rate using the same low concentrations required for individual molecule burst identification. In this work we present a new two-color smFRET approach using multispot excitation and detection. The donor excitation pattern is composed of 4 spots arranged in a linear pattern. The fluorescent emission of donor and acceptor dyes is then collected and refocused on two separate areas of a custom 8-pixel SPAD array. We report smFRET measurements performed on various DNA samples synthesized with various distances between the donor and acceptor fluorophores. We demonstrate that our approach provides identical FRET efficiency values to a conventional single-spot acquisition approach, but with a reduced acquisition time. Our work thus opens the way to high-throughput smFRET analysis on freely diffusing molecules.

In this paper, we propose and investigate a schottky tunneling source impact ionization MOSFET (STSIMOS) with enhanced device performance. STS-IMOS has silicide (NiSi) source to lower the breakdown voltage of conventional impact ionization MOS (IMOS). There is cumulative effect of both impact ionization and source induced tunneling for the current gating mechanism of the device. The silicide source offers immensely low parasitic resistance subsequently there is an increment in voltage drop across intrinsic region. This leads to appreciable lowering of breakdown and threshold voltage for STS-IMOS. Hence, it demonstrates enhanced device performance over conventional IMOS. Besides this for STS-IMOS the location of maximum electric field has shifted towards the source and now it is quite away from gate oxide. Hence, it shows high immunity against Vth fluctuations due to hot electron damage. Consequently, it is found that device reliability is also improved significantly.