Waveguiding Effect in Electroabsorption Modulators: Passivation Layers and Their Impact on Extinction Ratios

Waveguide structures of the stand‐alone electroabsorption (EA) modulator and the electroabsorption modulated laser (EML) are investigated using the 3D beam propagation method. The EA waveguide structures with InP‐based passivation layers show saturation in the extinction ratio (ER) due to the stray light traveling through the passivation layers. This paper demonstrates that narrower passivation layers suppress stray‐light excitation in the EA waveguide, increasing the ER. A taper structure in the isolation section of the EML waveguide can reduce the mode mismatch and suppress the excitation of the stray light, increasing the ER further. Low‐index‐polymer passivation layers can confine the mode more tightly in the active waveguide, yielding an even higher ER.     

Laser Process Proximity Correction for Improvement of Critical Dimension Linearity on a Photomask

We report on the improvement of critical dimension (CD) linearity on a photomask by applying the concept of process proximity correction to a laser lithographic process used for the fabrication of photomasks. Rule‐based laser process proximity correction (LPC) was performed using an automated optical proximity correction tool and we obtained dramatic improvement of CD linearity on a photomask. A study on model‐based LPC was executed using a two‐Gaussian kernel function and we extracted model parameters for the laser lithographic process by fitting the model‐predicted CD linearity data with measured ones. Model‐predicted bias values of isolated space (I/S), arrayed contact (A/C) and isolated contact (I/C) were in good agreement with those obtained by the nonlinear curve‐fitting method used for the rule‐based LPC.     

Insights into the Adhesive Mechanisms of Tree Frogs using Artificial Mimics

Elastic, microstructured surfaces (hydrophobic and hydrophilic) mimicking the surface structure of tree‐frog toe‐pads are fabricated. Their adhesion and friction behaviour in the presence of a liquid layer is evaluated and compared to flat controls. Tree‐frog‐like patterns are beneficial for wet adhesion only if the liquid does not wet the surface. The situation is different in friction, where the surface structure lead to significantly higher friction forces only if the liquid does wet the surface. Taking into account that tree‐frog attachment pads are hydrophilic and that their secretion wets all kind of surfaces, our results indicate that the surface structure in tree‐frog toe‐pads has been developed for climbing, when shear (friction) forces are involved. These results evidence the benefits and limitations of the surface design (microstructure and hydrophilicity) for adhesion and friction under wet conditions.     

Architectural Design Issues in a Clockless 32‐Bit Processor Using an Asynchronous HDL

As technology evolves into the deep submicron level, synchronous circuit designs based on a single global clock have incurred problems in such areas as timing closure and power consumption. An asynchronous circuit design methodology is one of the strong candidates to solve such problems. To verify the feasibility and efficiency of a large‐scale asynchronous circuit, we design a fully clockless 32‐bit processor. We model the processor using an asynchronous HDL and synthesize it using a tool specialized for asynchronous circuits with a top‐down design approach. In this paper, two microarchitectures, basic and enhanced, are explored. The results from a pre‐layout simulation utilizing 0.13‐μm CMOS technology show that the performance and power consumption of the enhanced microarchitecture are respectively improved by 109% and 30% with respect to the basic architecture. Furthermore, the measured power efficiency is about 238 μW/MHz and is comparable to that of a synchronous counterpart.