Thermal Ground Plane for Chip-Level Electronics Cooling

The three-dimensional thermal ground plane was developed in response to the needs of high-power density electronics applications in which heat must be removed as close to the chip surface as possible. The novel design for this planar cooling device was proposed with three key innovations in the evaporator, wick, and reservoir layer, which provided enhanced and reliable cooling performance without wick dryout and back flows. For the evaporator and reservoir layer, a combination of a tapered channel and a triple-spike microstructure was designed to break up the pinned meniscus at the end of the vapor and liquid channels. The overall microstructure had three spikes where the main liquid meniscus was separated by a middle spike and then continued to flow between the tapered walls of the middle and side spikes. For the wick layer, a nanowire-integrated microporous silicon membrane was developed to overcome dryout by driving the coolant out of the channels and spreading the coolant on top of the wick surface with the assistance of extended capillary action. This innovative design used nanowires to extend and enhance capillary force, especially at the end of the pores where the coolant was pinned and unable to overflow out of the pores. The chronic dryout problem in micro cooling devices could be solved by these innovative designs. To analyze the thermal-fluid system, fluid dynamic and phase-change models were used to calculate thermodynamic and fluidic properties, such as operating temperature, pressure, vapor-liquid interface radius of curvature, and rate of bubble formation. The microscale heat conduction theory derived from traditional Fourier's law with classical size effect and effective medium theory were used to calculate the thermal conductivities of nanowires and porous silicon wick in the cross-plane direction, respectively. The theoretical results of porous silicon showed good agreement with the experimental results measured by the 3ù technique, demonstrating the reduction of thermal conductivity from bulk silicon. Cooling performance of the developed device was demonstrated experimentally with a micro ceramic heater, thermocouple modules, and microfabrication techniques, including photoelectrochemical etching to create porous silicon, deep reactive-ion etching to form a thin wick membrane, and hydrothermal synthesis to grow nanowires on top of the wick membrane. This study shows the feasibility of reliable, continuous, and high-performance micro cooling devices using enhanced capillary forces to address the increasing requirements of thermal management for chip-level electronics

3D-printing-assisted flexible pressure sensor with a concentric circle pattern and high sensitivity for health monitoring

Abstract In this study, a flexible pressure sensor is fabricated using polydimethylsiloxane (PDMS) with a concentric circle pattern (CCP) obtained through a fused deposition modeling (FDM)-type three-dimensional (3D) printer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the active layer. Through layer-by-layer additive manufacturing, the CCP surface is generated from a thin cone model with a rough surface by the FDM-type 3D printer. A novel compression method is employed to convert the cone shape into a planar microstructure above the glass transition temperature of a polylactic acid (PLA) filament. To endow the CCP surface with conductivity, PDMS is used to replicate the compressed PLA, and PEDOT:PSS is coated by drop-casting. The size of the CCP is controlled by changing the printing layer height (PLH), which is one of the 3D printing parameters. The sensitivity increases as the PLH increases, and the pressure sensor with a 0.16 mm PLH exhibits outstanding sensitivity (160 kPa−1), corresponding to a linear pressure range of 0–0.577 kPa with a good linearity of R 2 = 0.978, compared to other PLHs. This pressure sensor exhibits stable and repeatable operation under various pressures and durability under 6.56 kPa for 4000 cycles. Finally, monitoring of various health signals such as those for the wrist pulse, swallowing, and pronunciation of words is demonstrated as an application. These results support the simple fabrication of a highly sensitive, flexible pressure sensor for human health monitoring

Structural Effects of Crumpled Graphene and Recent Developments in Comprehensive Sensor Applications: A Review

Graphene is a 2D honeycomb lattice consisting of a single layer of carbon atoms. Graphene has become one of the most preferred materials for sensor development due to its exceptional electrical, mechanical, and thermal characteristics. Nonetheless, little consideration is given to the production and use of crumpled graphene. Specifically, the crumpled graphene structure is a good choice for enhancing sensors’ sensitivity and structural deformability by reducing interfacial stress, avoiding electrical failure, and enhancing surface areas. This review article provides an overview of various synthesis processes using crumpled graphene and specifies a brief idea to control crumpled formation in graphene structure for sensing applications in recent years. Furthermore, it summarizes the problems encountered in previously published research articles during the fabrication and performance of sensors with a brief discussion of fundamental mechanics and topological aspects concerning crumpling patterns with sensing performance. It also highlights the current status of crumpling techniques and their effects on developing different sensors using existing crumpling methods, controlled crumpling designs, and sensing methodologies for future applications