Design of High-Speed, Low-Power Sensing Circuits for Nano-Scale Embedded Memory.

This paper comparatively reviews sensing circuit designs for the most widely used embedded memory, static random-access memory (SRAM). Many sensing circuits for SRAM have been proposed to improve power efficiency and speed, because sensing operations in SRAM dominantly determine the overall speed and power consumption of the system-on-chip. This phenomenon is more pronounced in the nanoscale era, where SRAM bit-cells implemented near minimum-sized transistors are highly influenced by variation effects. Under this condition, for stable sensing, the control signal for accessing the selected bit-cell (word-line, WL) should be asserted for a long time, leading to increases in the power dissipation and delay at the same time. By innovating sensing circuits that can reduce the WL pulse width, the sensing power and speed can be efficiently improved, simultaneously. Throughout this paper, the strength and weakness of many SRAM sensing circuits are introduced in terms of various aspects-speed, area, power, etc.

Tunable Multifunctional Thermal Metamaterials: Manipulation of Local Heat Flux via Assembly of Unit-Cell Thermal Shifters.

Thermal metamaterials, designed by transformation thermodynamics are artificial structures that can actively control heat flux at a continuum scale. However, fabrication of them is very challenging because it requires a continuous change of thermal properties in materials, for one specific function. Herein, we introduce tunable thermal metamaterials that use the assembly of unit-cell thermal shifters for a remarkable enhancement in multifunctionality as well as manufacturability. Similar to the digitization of a two-dimensional image, designed thermal metamaterials by transformation thermodynamics are disassembled as unit-cells thermal shifters in tiny areas, representing discretized heat flux lines in local spots. The programmed-reassembly of thermal shifters inspired by LEGO enable the four significant functions of thermal metamaterials-shield, concentrator, diffuser, and rotator-in both simulation and experimental verification using finite element method and fabricated structures made from copper and PDMS. This work paves the way for overcoming the structural and functional limitations of thermal metamaterials.

Effect of alumina composition and surface integrity in alumina/epoxy composites on the ultrasonic attenuation properties.

We report a method of fabricating backing blocks for ultrasonic imaging transducers, using alumina/epoxy composites. Backing blocks contain scatterers such as alumina particles interspersed in the epoxy matrix for the effective scattering and attenuation of ultrasound. Here, the surface integrity can be an issue, where the composite material may be damaged during machining because of differences in strength, hardness and brittleness of the hard alumina particles and the soft epoxy matrix. Poor surface integrity results in the formation of air cavities between the backing block and the piezoelectric element upon assembly, hence the increased reflection off the backing block and the eventual degradation in image quality. Furthermore, with an issue of poor surface integrity due to machining, it is difficult to increase alumina as scatterers more than a specific mass fraction ratio. In this study, we increased the portion of alumina within epoxy matrix by obtaining an enhanced surface integrity using a net shape fabrication method, and verified that this method could allow us to achieve higher ultrasonic attenuation. Backing blocks were net-shaped with various mass fractions of alumina to characterize the formability and the mechanical properties, including hardness, surface roughness and the internal micro-structure, which were compared with those of machined backing blocks. The ultrasonic attenuation property of the backing blocks was also measured.