Graphene FET on diamond for high-frequency electronics

Transistors operating at high frequencies are the basic building blocks of millimeter-wave communication and sensor systems. The high velocity and mobility of carriers in graphene can open way for ultra-fast group IV transistors with similar or even better performance than can be achieved with III-V based semiconductors. However, the progress of high-speed graphene transistors has been hampered due to fabrication issues, influence of adjacent materials, and self-heating effects. Here, we report a graphene field-effect transistor (FET) on a diamond substrate, with a $f_{max}$ up to 54 GHz for a gate length of 500 nm. The high thermal conductivity of diamond provides an efficient heat-sink, and its relatively high optical-phonon energy improves saturation velocity of carriers in the graphene channel. Moreover, we show that graphene FETs on diamond, with different gate lengths, exhibit excellent scaling behavior. These results indicate that graphene FETs on diamond technology can reach sub-terahertz frequency performance.Comment: 16 pages, 5 figures, lette

Transport behavior of holes in boron delta-doped diamond structures

Boron delta-doped diamond structures have been synthesized using microwave plasma chemical vapor deposition and fabricated into FET and gated Hall bar devices for assessment of the electrical characteristics. A detailed study of variable temperature Hall, conductivity, and field-effect mobility measurements was completed. This was supported by Schr€dinger-Poisson and relaxation time o calculations based upon application of Fermi’s golden rule. A two carrier-type model was developed with an activation energy of $0.2 eV between the delta layer lowest subband with mobility$1 cm2/Vs and the bulk valence band with high mobility. This new understanding of the transport of holes in such boron delta-doped structures has shown that although Hall mobility as high as 900 cm2/Vs was measured at room temperature, this dramatically overstates the actual useful performance of the device

A Quantum Anomaly For Rigid Particles

Canonical quantisation of rigid particles is considered paying special attention to the restriction on phase space due to causal propagation. A mixed Lorentz-gravitational anomaly is found in the commutator of Lorentz boosts with world-line reparametrisations. The subspace of gauge invariant physical states is therefore not invariant under Lorentz transformations. The analysis applies for an arbitrary extrinsic curvature dependence with the exception of only one case to be studied separately. Consequences for rigid strings are also discussed.Comment: (replaces previous unpritable version corrupted mailer) 12 pages (Plain TeX), DTP-92/3

Nonlinear Passive Control of a Wave Energy Converter Subject to Constraints in Irregular Waves

This paper investigates a passive control method of a point absorbing wave energy converter by considering the displacement and velocity constraints under irregular waves in the time domain. A linear generator is used as a power take-off unit, and the equivalent damping force is optimized to improve the power production of the wave energy converter. The results from nonlinear and linear passive control methods are compared, and indicate that the nonlinear passive control method leads to the excitation force in phase with the velocity of the converter that can significantly improve the energy production of the converter

A Limit Study of Thread-Level Speculation in JavaScript Engines --- Initial Results

JavaScript is a programming language for interactive clientside functionalities in web applications. It is a sequential pro- gramming language, so it cannot take advantage of multicore processors. Previously Thread-Level Speculation has been used to take advantage of multicore processors for JavaScript execution in web applications with promising results execu- tion time wise, but with a large memory overhead. In this study we have evaluated the effects of limiting the amount of memory, the number of threads and the depth of specula- tion in Thread-Level Speculation. Our results indicate that we can tune these parameters to improve execution time and reduce the memory overhead