We fabricated a silicon microrefrigerator on a 500-mu m-thick substrate with the standard integrated circuit (IC) fabrication process. The cooler achieves a maximum cooling of 1 degrees C below ambient at room temperature. Simulations show that the cooling power density for a 40 x 40 mu m(2) device exceeds 500 W/cm(2). The unique three-dimensional (3-D) geometry, current and heat spreading, different from conventional one-dimensional (1-D) thermoelectric device, contribute to this large cooling power density. A 3-D finite element electrothermal model is used to analyze non-ideal factors inside the device and predict its limits. The simulation results show that in the ideal situation, with low contact resistance, bulk silicon with 3-D geometry could cool similar to 20 degrees C with a cooling power density of 1000 W/cm(2) despite the low thermoelectric figure-of-merit (ZT) of the material. The large cooling power density is due to the geometry dependent heat and current spreading in the device. The non-uniformity of current and Joule heating inside the substrate also contributes to the maximum cooling of silicon microrefrigerator, exceeding 30% limit given in one-dimensional thermoelectric theory Delta T-max = 0.5ZT(c)(2) where T-c is the cold side temperature. These devices can be used c to remove hot spots on a chip.

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## Scholarly Works (17 results)

We demonstrate a three-dimensional (3D) bulk silicon microcooler, which has the advantages of high cooling power densities and is less dependent on thermoelectric element's thickness as compared with the same device with one-dimensional (1D) geometry. We measured a maximum cooling of 1.2 degreesC for a 40x40 mum(2) area bulk silicon microcooler device, which is equivalent to an estimated cooling power density of 580 W/cm(2). In this unique geometry, both current and heat spreading in 3D allows the maximum cooling temperature to exceed the conventional 1D thermoelectric model's theoretical limit 0.5 ZT(c)(2). (C) 2004 American Institute of Physics.

A three-dimensional (3-D) electrothermal model was developed to study the InP-based thin-film In0.53Ga0.47As/In0.52Al0.48As superlattice (SL) microrefrigerators for various device sizes, ranging from 40 x 40 to 120 x 120 mu m(2). We discussed both the maximum cooling and cooling power densities (CPDs) for experimental devices, analyzed their nonidealities, and proposed an optimized structure. The simulation results demonstrated that the experimental devices with an optimized structure can achieve a maximum cooling of 3 degrees C, or equivalently, a CPD over 300 W/cm(2). Furthermore, we found it was possible to achieve a maximum cooling of over 10 degrees C; equivalently, a CPD over 900 W/cm(2), when the figure of merit (ZT) of InGaAs/InAlAs SL was enhanced five times with nonconserved lateral momentum structures. Besides monolithic growth, we also proposed a fusion bonding scheme to simply bond the microrefrigerator chip on the back of the hot spots, defined as two-chip integration model in this paper. The cooling effect of this model was analyzed using ANSYS simulations.

We have studied experimentally and theoretically the cross-plane Seebeck coefficient of short period InGaAs/InAlAs superlattices with doping concentrations ranging from 2x10(18) up to 3x10(19) cm(-3). Measurements are performed with integrated thin film heaters in a wide temperature range of 10-300 K. It was interesting to find out that contrary to the behavior in bulk material the Seebeck coefficient did not decrease monotonically with the doping concentration. We did not observe a sign change in the Seebeck coefficient at dopings where the Fermi energy is just above a miniband. This is a sign that electrons' lateral momentum is conserved in the transport perpendicular to superlattice layers. A preliminary theory of thermoelectric transport in superlattices in the regime of miniband formation has been developed to fit the experimental results.

In this paper, we explore electron filtering as a technique to increase the Seebeck coefficient and the thermoelectric power factor of heterostructured materials over that of the bulk. We present a theoretical model in which the Seebeck coefficient and the power factor can be increased in an In0.53Ga0.47As-based composite material. Experimental measurements of the cross-plane Seebeck coefficient are presented and confirm the importance of the electron filtering technique to decouple the electrical conductivity and Seebeck coefficient to increase the thermoelectric power factor.

In this paper, we addressed heating problems in integrated circuits (ICs) and proposed a thin-film thermionic cooling solution using Si/SiGe superlattice microrefrigerators. We compared our technology with the current most common solution, thermoelectric coolers, by strengthening the advantages of its compatible fabrication process as ICs for easy integration, small footprint in the order of similar to 100 x 100 mu m(2), high cooling power density, 600 W/cm(2) and fast transient response less than 40 mu s. The thermoreflectance imaging also demonstrated its localized cooling. All these features combined together to make these microrefrigerators; a very promising application for on-chip temperature control, removing hot spots inside IC.

We studied the cross-plane lattice and electronic thermal conductivities of superlattices made of InGaAlAs and InGaAs films, with the latter containing embedded ErAs nanoparticles (denoted as ErAs:InGaAs). Measurements of total thermal conductivity at four doping levels and a theoretical analysis were used to estimate the cross-plane electronic thermal conductivity of the superlattices. The results show that the lattice and electronic thermal conductivities have marginal dependence on doping levels. This suggests that there is lateral conservation of electronic momentum during thermionic emission in the superlattices, which limits the fraction of available electrons for thermionic emission, thereby affecting the performance of thermoelectric devices. (c) 2006 American Institute of Physics.

We report a wafer scale approach for the fabrication of thin-film power generators composed of arrays of 400 p and n type ErAs:InGaAs/InGaAlAs superlattice thermoelectric elements. The elements incorporate ErAs metallic nanoparticles into the semiconductor superlattice structure to provide charge carriers and create scattering centers for phonons. p- and n-type ErAs:InGaAs/InGaAlAs superlattices with a total thickness of 5 mu m were grown on InP substrate using molecular beam epitaxy. The cross-plane Seebeck coefficients and cross-plane thermal conductivity of the superlattice were measured using test pattern devices and the 3 omega method, respectively. Four hundred element power generators were fabricated from these 5 mu m thick, 200 mu mx200 mu m in area superlattice elements. The output power was over 0.7 mW for an external resistor of 100 Omega with a 30 K temperature difference drop across the generator. We discuss the limitations to the generator performance and provide suggestions for improvements. (c) 2006 American Institute of Physics.

We characterize cross-plane and in-plane Seebeck coefficients for ErAs:InGaAs/InGaAlAs superlattices with different carrier concentrations using test patterns integrated with microheaters. The microheater creates a local temperature difference, and the cross-plane Seebeck coefficients of the superlattices are determined by a combination of experimental measurements and finite element simulations. The cross-plane Seebeck coefficients are compared to the in-plane Seebeck coefficients and a significant increase in the cross-plane Seebeck coefficient over the in-plane Seebeck coefficient is observed. Differences between cross-plane and in-plane Seebeck coefficients decrease as the carrier concentration increases, which is indicative of heterostructure thermionic emission in the cross-plane direction. (c) 2007 American Institute of Physics.