X-ray radiation effects in multilayer epitaxial graphene

International audienceWe characterize multilayer graphene grown on C-face SiC before and after exposure to a total ionizing dose (TID) of 12 Mrad(SiO2) using a 10 keV X-ray source. While we observe the partial peeling of the top graphene layer and the appearance of a modest Raman D-peak, we find that the electrical characteristics (mobility, sheet resistivity, free carrier concentration) of the material are mostly unaffected by radiation exposure. Combined with X-ray photoelectron spectroscopy (XPS) data showing numerous carbon-oxygen bonds after irradiation, we conclude that the primary damage mechanism is through surface etching from reactive oxygen species created by the X-rays

Lifetime studies of 130nm nMOS transistors intended for long-duration, cryogenic high-energy physics experiments

Future neutrino physics experiments intend to use unprecedented volumes of liquid argon to fill a time projection chamber in an underground facility. To increase performance, integrated readout electronics should work inside the cryostat. Due to the scale and cost associated with evacuating and filling the cryostat, the electronics will be unserviceable for the duration of the experiment. Therefore, the lifetimes of these circuits must be well in excess of 20 years. The principle mechanism for lifetime degradation of MOSFET devices and circuits operating at cryogenic temperatures is via hot carrier degradation. Choosing a process technology that is, as much as possible, immune to such degradation and developing design techniques to avoid exposure to such damage are the goals. This requires careful investigation and a basic understanding of the mechanisms that underlie hot carrier degradation and the secondary effects they cause in circuits. In this work, commercially available 130nm nMOS transistors operating at cryogenic temperatures are investigated. The results show that the difference in lifetime for room temperature operation and cryogenic operation for this process are not great and the lifetimes at both 300K and at 77K can be projected to more than 20 years at the nominal voltage (1.5V) for this technology

High-Speed Single-Event Current Transient Measurements in SiGe HBTs

Time-resolved ion beam induced charge reveals heavy ion response of IBM 5AM SiGe HBT: 1) Position correlation. 2) Unique response for different bias schemes. 3) Similarities to TPA pulsed-laser data. Heavy ion broad-beam transients provide more realistic device response: 1) Feedback using microbeam data 2) Overcome existing issues of LET and ion range with microbeam Both micro- and broad-beam data sets yield valuable input for TCAD simulations. Uncover detailed mechanisms for SiGe HBTs and other devices fabricated on lightly-doped substrates

Integrated motor drives: state of the art and future trends

With increased need for high power density, high efficiency and high temperature capabilities in Aerospace and Automotive applications, Integrated Motor Drives (IMD) offers a potential solution. However, close physical integration of the converter and the machine may also lead to an increase in components temperature. This requires careful mechanical, structural and thermal analysis; and design of the IMD system. This paper reviews existing IMD technologies and their thermal effects on the IMD system. The effects of the power electronics (PE) position on the IMD system and its respective thermal management concepts are also investigated. The challenges faced in designing and manufacturing of an IMD along with the mechanical and structural impacts of close physical integration is also discussed and potential solutions are provided. Potential converter topologies for an IMD like the Matrix converter, 2-level Bridge, 3-level NPC and Multiphase full bridge converters are also reviewed. Wide band gap devices like SiC and GaN and their packaging in power modules for IMDs are also discussed. Power modules components and packaging technologies are also presented

Operation of SiGe bipolar technology at cryogenic temperatures

The recent introduction of silicon-germanium (SiGe) alloys has proven exceptionally promising for achieving excellent bipolar transistor performance at cryogenic temperatures, while maintaining the cost and yield advantages traditionally associated with silicon (Si) manufacturing. In this paper we review the features of silicon-germanium heterojunction bipolar transistors (SiGe HBTs) which make them particularly suitable for cryogenic operation. Using dc and ac experimental results, we also address the issues associated with profile optimization of SiGe HBTs for the cryogenic environment, the potential for cryogenic SiGe BiCMOS technologies, and present new results on liquid-helium temperature operation of SiGe HBTs. We conclude that SiGe HBT technology offers significant leverage for future cryogenic digital, analog and mixed-signal applications requiring the highest levels of performance

Optimization of Early Voltage for Cooled SiGe HBT Precision Current Sources

The influence of Ge profile shape on the temperature characteristics of two key analog transistor parameters, Early voltage (VA) and current gain-Early voltage product (βVA), in SiGe HBTs have been studied over the temperature range of 300K-77K using SCORPIO, a transistor simulation tool calibrated to measured data [1]. A new version of SPICE that accounts for the temperature dependence of VA was used to model the various SiGe HBTs simulated and thereby evaluate the cryogenic performance of SiGe HBT precision current sources, which are strongly influenced by the variations in both β and VA. Results clearly indicate that the cryogenic performance of these SiGe current sources can be significantly improved by using a graded Ge profile instead of a constant Ge profile in the base region of the HBT

Electron impact-ionization effects in UHV/CVD SiGe HBT's in the temperature range of 300 to 83 K

The electron impact-ionization rates (M-1) in SiGe HBT's are investigated using a new technique in the temperature range of 300 to 83K. In the new technique, the initial current for avalanche multiplication is explicitly controlled in the presence of Early effect and self-heating, and the low VCB limitation set by the open emitter current ICBO is removed. With cooling, M-1 increases first, and then saturates. when T < 117K. A 2.3V critical reverse CB voltage at which base current reversal occurs is observed at 83K, which is sufficiently high for today's bipolar and BiCMOS logic applications. Comparison with the silicon control devices suggests that the M-1 is not increased by the incorporation of SiGe, despite its smaller bandgap, indicating that SiGe HBT's are suitable for RF power applications

The effect of 63 MeV hydrogen ion irradiation on 65 GHz UHV/CVD SiGe HBT BiCMOS technology

Two thousand arrays of second generation (6HP) silicon-germanium heterojunction bipolar transistors (SiGe HBTs) were exposed to 63 MeV hydrogen ions at a fluence ranging from 1 x 10(12) to 5 x 10(13) cm(-2). The dc electrical measurements, such as Gummel characteristics, excess base current (Delta I(B) = I(Bpost) - I(Bpre)), current gain (h(FE)), neutral base recombination, avalanche multiplication factor (M-1) and output characteristics (V(CE)-I(C)), were systematically studied before and after hydrogen ion irradiation. The SiGe HBT showed 80% degradation in forward-mode dc current gain after a total dose of 5 x 10(13) cm(-2) hydrogen ion irradiation

Numerical simulation of SiGe HBT's at cryogenic temperatures

This paper describes SCORPIO, a new one-dimensional, drift-diffusion simulator for modeling silicon-germanium heterojunction bipolar transistors (SiGe HBT's) over a wide temperature range (77-400K). SCORPIO will be used to investigate fundamental low-temperature device physics problems and key device design issues. Comparisons of simulation results with experimental measurements are being used to ensure accurate model calibration