Graded-barrier graded-channel InP pseudomorphic power HEMT with 40% power added efficiency and 200 mW output power at 60 GHz
Summary form only given. We present state-of-the-art power and PAE results of InGaAs-InAlAs-InP HEMTs with optimized graded channel and graded Schottky barrier layers which demonstrate, for the first time, that InP-based HEMTs have a considerably better power/PAE combination than GaAs-based HEMTs at V-band. The 0.15 /spl mu/m gate length, eight gate finger, 500 /spl mu/m wide InP HEMTs were measured in a fixture under continuous wave (CW) conditions and showed 23 dBm (200 mW) output power and 40% PAE at 60 GHz with an input power of 17 dBm, a drain bias of 3 V, and a drain current of 125 mA. These results represent the best reported V-band power/PAE performance to date, and a comparison of these results with previously reported results for both InP- and GaAs-based HEMTs is shown. Our state-of-the-art results are attributed to the use of an optimized heterostructure incorporating pseudomorphic graded channel and graded Schottky barrier layers, and the use of compact 15 /spl mu/m/spl times/25 /spl mu/m dry etched through-substrate vias (substrate thickness of 50 /spl mu/m). The heterostructure was designed to achieve high gain, current (Imax) and breakdown voltage; all of which are requirements for a device with high power and PAE.
Analytical Model for 2DEG Density in Graded MgZnO/ZnO Heterostructures With Cap Layer
In this paper, we develop a generic analytical model for 2-D electron gas (2DEG) density (<inline-formula> <tex-math notation="LaTeX">${\mathrm{n}}_{\mathrm{s}})$ </tex-math></inline-formula> and threshold voltage (<inline-formula> <tex-math notation="LaTeX">${\mathrm{V}}_{ \mathrm{\scriptscriptstyle OFF}})$ </tex-math></inline-formula> of a fully strained graded ZnO-based heterostructure with a cap layer. The model is based on the continuity of electric field at the interfaces of different layers, dominant piezoelectric and spontaneous polarization components in different layers, Mg composition, and layer thickness. The generic model can be reduced to a simplified bilayer structure for calculating <inline-formula> <tex-math notation="LaTeX">${\mathrm{n}}_{\mathrm{s}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${\mathrm{V}}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula>. Results show that the graded heterostructure can result in higher values of 2DEG density and <inline-formula> <tex-math notation="LaTeX">${\mathrm{V}}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> (absolute values) compared to the bilayer structure. A careful optimization of the structure is required to achieve a trade-off between <inline-formula> <tex-math notation="LaTeX">${\mathrm{n}}_{\mathrm{s}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${\mathrm{V}}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula>. An analytical expression of polarization charge density at buffer–barrier interface to better fit the experimental data available in the literature is also proposed. The model will be suitable for the design optimization of 2DEG density and <inline-formula> <tex-math notation="LaTeX">${\mathrm{V}}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> for ZnO-based heterostructures.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.