Mitigation of Single-Event Effects in SiGe-HBT Current-Mode Logic Circuits.

It has been known that negative feedback loops (internal and external) in a SiGe heterojunction bipolar transistors (HBT) DC current mirrors improve single-event transient (SET) response; both the peak transient current and the settling time significantly decrease. In the present work, we demonstrate how radiation hardening by design (RHBD) techniques utilized in DC bias blocks only (current mirrors) can also improve the SET response in AC signal paths of switching circuits (e.g., current-mode logic, CML) without any additional hardening in those AC signal paths. Four CML circuits both with and without RHBD current mirrors were fabricated in 130 nm SiGe HBT technology. Two existing RHBD techniques were employed separately in the current mirrors of the CML circuits: (1) applying internal negative feedback and (2) adding a large capacitor in a sensitive node. In addition, these methods are also combined to analyze the overall SET performance. The single-event transients of the fabricated circuits were captured under the two-photon-absorption laser-induced single-event environment. The measurement data clearly show significant improvements in SET response in the AC signal paths of the CML circuits by using the two radiation hardening techniques applied only in DC current mirrors. The peak output transient current is notably reduced, and the settling time upon a laser strike is shortened significantly.

Using Bessel beams and two-photon absorption to predict radiation effects in microelectronics.

Pulsed-laser testing is an attractive tool for studying space-based radiation effects in microelectronics because it provides a high degree of spatial resolution and is more cost-effective than conventional accelerator-based testing. However, quantitatively predicting the effects of radiation is challenging for this optical method. A new approach to pulsed-laser testing is presented, which addresses these challenges by using a Bessel beam and carrier generation via two-photon absorption. By producing a carrier distribution in the device under test that is similar to that of a heavy ion, this optical approach aims to quantitatively predict the response of the device under heavy ion tests that represent space radiation. Furthermore, the carrier distribution can be accurately described using a single analytic expression thereby enabling the laser to be tuned to emulate a specific heavy ion. Herein, we describe the modifications made to an existing pulsed-laser setup to generate this carrier distribution, characterize this distribution using a novel method that provides sub-micron spatial resolution, and provide the equations that describe the distribution. Finally, we use this method to study a silicon photodiode and find that the transient response of the device shows strong agreement with the response generated using heavy ions.

On the dual phosphorescence of xanthone and chromone in glassy hydrocarbon hosts.

Trace quantities of hydrogen-bonding impurities in otherwise highly purified and dried glassy hydrocarbon matrices at 77 K can modify the relative triplet state energy levels, and hence the photophysical properties of two aromatic ketones, xanthone and chromone, to the extent that the intrinsic spectroscopic properties are obscured. The intrinsic spectroscopic properties of each are revealed in multicrystalline n-alkane Shpol'skii matrices, and also can be observed in rigorously purified and dried hydrocarbon glasses at 77 K. The extreme sensitivity to stoichiometric, and even substoichiometric quantities of hydrogen-bonding impurities arises from the near-degeneracy of the two lowest-lying triplet states, and the sensitive nature of the n→π* blueshift phenomena to specific hydrogen-bonding interactions.

Photoluminescence properties of conjugated phenylacetylene monodendrons in thin films.

We report the absorption, photoluminescence (PL), and time-dependent PL of thin films of conjugated phenylacetylene monodendrons at both room temperature and at cryogenic temperature. We find that the PL properties of the monodendron thin films are significantly different from their fluorescence in dilute solution due to the presence of interactions between monodendrons in the thin film. These interactions lead to aggregate species in the thin films, which result in broader PL spectra and lower PL quantum yields than for monodendrons in dilute solution. Evidence for excimer-like aggregates in the monodendron thin films is found from time-resolved PL spectra.

Optical and photophysical properties of light-harvesting phenylacetylene monodendrons based on unsymmetrical branching.

The optical and photophysical properties of phenylacetylene dendritic macromolecules based on unsymmetrical branching are investigated using steady-state and time-dependent spectroscopy. Monodendrons, up to the fourth generation, are characterized with and without a fluorescent perylene trap at the core. The higher generation monodendrons without the perylene trap exhibit high molar extinction coefficients (>10(5) M(-1) cm(-1)) and high fluorescence quantum yields (65-81%). When a perylene trap is placed at the core, then the monodendrons typically exhibit high energy transfer quantum yields (approximately 90%), as well as subpicosecond time scale excited-state dynamics, as evidenced by ultrafast pump-probe measurements. The photophysical properties of the unsymmetrical monodendrons are compared to those of phenylacetylene monodendrons with symmetrical branching, which have been described recently. The high fluorescence quantum yields and large energy transfer quantum efficiencies exhibited by the unsymmetrical monodendrons suggest they have potential for applications in molecular-based photonics devices.