Reduction Of Thermal Impedance Research Articles

Vertically aligned carbon fibers-penetrated phase change thermal interface materials with high thermal conductivity for chip heat dissipation

Phase change thermal interface materials (PCTIMs) are receiving increasing attention but suffer from low thermal conductivity and are challenging to improve significantly. Here, vertically aligned short-cut carbon fibers (VASCFs) were employed for the first time to develop PCTIMs with high thermal conductivity. The most effective thermal conductivity enhancement was achieved by VASCFs, which were attributed to providing complete heat transfer paths, further verified by the finite element simulation. VASCFs were thus incorporated into an optimized mixture of silicon rubber (SR) and paraffin (PA) to fabricate form-stable phase change thermal pads. The VASCFs/PA/SR thermal pads achieved a thermal conductivity of as high as 7.00 W/(m·K), much higher than that of the previously reported PCTIMs. More significantly, it is revealed that the reduction in thermal impedance induced by the phase change of PA, led to the better heat dissipation performance of VASCFs/PA/SR, thus making the VASCFs/PA/SR phase change thermal pads show potential in practical applications.

Evaluation of the thermal performance of high-power LED using magnesium oxide thin film as heat spreader

The spin coating technique was used to synthesize MgO thin film on aluminium substrates. XRD diffraction proved the presence of (200), (220) and (222) MgO phase orientations. Film thickness (370 nm), the crystal size of 17.14 nm, low surface roughness of 12.8 nm and thermal conductivity (22.68 W/mK) were recorded for MgO film sample prepared from 0.6 M concentration. A noticeable reduction in junction temperature (ΔTJ - 20.11 °C) and total thermal resistance (ΔRth-tot - 3.22 K/W) were recorded for LED fixed on 0.6 M MgO thin film sample. 8% reduction of thermal impedance was also recorded for the prepared film and proving it is free from internal structure degradation. Overall, a noticeable improvement in thermal performance of high-power LED was achieved with MgO thin film as a heat spreader and suggested it as a future alternative to the commercially available film-based heat spreader.

Silver nanowire array-polymer composite as thermal interface material

Silver nanowire arrays embedded inside polycarbonate templates are investigated as a viable thermal interface material for electronic cooling applications. The composite shows an average thermal diffusivity value of 1.89×10−5 m2 s−1, which resulted in an intrinsic thermal conductivity of 30.3 W m−1 K−1. The nanowires’ protrusion from the film surface enables it to conform to the surface roughness to make a better thermal contact. This resulted in a 61% reduction in thermal impedance when compared with blank polymer. An ∼30 nm Au film on the top of the composite was found to act as a heat spreader, reducing the thermal impedance further by 35%. A contact impedance model was employed to compare the contact impedance of aligned silver nanowire-polymer composites with that of aligned carbon nanotubes, which showed that the Young’s modulus of the composite is the defining factor in the overall thermal impedance of these composites.

Novel HBT with reduced thermal impedance

Heterojunction bipolar transistors have been fabricated using a novel process in which the majority of the front side of the chip is metallized to serve as the groundplane. The completed chip is assembled inverted so that the emitters are next to the heat sink; base and collector are contacted using through-wafer vias and microstrip lines on the back side of the chip. These devices show a 50% reduction in thermal impedance compared to conventionally fabricated devices and have achieved power densities of 10 W/mm of emitter length. Such devices are expected to have substantially lower emitter inductance as well, which may lead to improved gain at higher frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-power parallel-array IMPATT diodes

Fabrication of parallel arrays of silicon IMPATT diodes in which the arrays are formed in a single diode chip is described. The technique includes formation of an integral heatsink for the diode arrays during wafer processing. For a given total active device area, the use of a parallel array of smaller diodes, rather than one large diode, allows a significant reduction in thermal impedance and consequently larger power-dissipation capability. The contribution shown in the letter is the ease and economy with which parallel arrays on an integral heatsink can be fabricated and handled as a single entity. In a diode operated at 6.4 GHz, 3.5 W of c.w. output power has been achieved with a room-temperature copper heatsink and a junction temperature of about 280°C.