Chih-Kuang Yu

Thermal conductivity of Si/SiGe superlattice films

We have evaluated the thermal conductivity of Si/SiGe superlattice films by theoretical analysis and experiment. In experiments, the ultrahigh vacuum chemical vapor deposition is employed to form the Si/Si0.71Ge0.29 and Si/Si0.8Ge0.2 superlattice films. The cross-plane thermal conductivities of these superlattice films are measured based on the 3ω method. In the theoretical analysis, the phonon transport in Si/Si1−xGex superlattice film is explored by solving the phonon Boltzmann transport equation. The dependence of the thermal conductivity of the Si/Si1−xGex superlattice films on the superlattice period, the ratio of layer thicknesses, and the interface roughness is of interest. The calculations show that when the layer thickness is on the order of one percentage of the mean free path or even thinner, the phonons encounter few intrinsic scatterings and consequently concentrate in the directions having high transmissivities. Nonlinear temperature distributions are observed near the interfaces, arising fr...

High efficiency silicon-based high power LED package integrated with micro- thermoelectric device

A new thermal management application of silicon-based thermoelectric (TE) cooler integrated with high power light emitting diode (LED) is investigated in present study. The silicon-based TE cooler herein is fabricated by MEMS fabrication technology and flip-chip assembly process that is used for high power LED cooling. An electrical-thermal conversion method is used to estimate the junction temperature of LED. Moreover, the integrating sphere is also used to measure the light efficiency of LED. The thermal images photographed by infrared camera demonstrated the cooling function of the silicon-based TE devices. The results also show that high power LED integrated with silicon-based thermoelectric cooler package can effectively reduce the thermal resistance to zero. In addition, the light efficiency of the LED (1 W) will increase under low TE cooler input power (0.55 W), which is about 1.3 times of that without TE cooler packaging.

Characteristics of Thermal Resistance for High Power LEDs

In this paper the accurate and fast measurement equipment was developed and applied to study the thermal characteristics of high power LEDs. The forward-voltage based method was conducted to measure the junction temperature of high power LEDs. Conduction type method is adopted to measure the temperature sensitivity parameter (TSP) with small magnitude of error compared with the traditional method. The experiment time was reduced from 3~4 hours to 10 minutes for one sample. It was demonstrated that the repeatability of the measurement system was well after the repeatability test. LEDs used here were 5 W single chip LED and 50 W multi-chip LED with 36 chips inside the LED. Thermal resistance of junction-to-case as function of input power and case temperature was discussed. It was shown that the 5 W LED revealed an increasing trend of thermal resistance with the input power at each case temperature but the contrary trend of 5OW LED. The results also exhibited the dependency of thermal resistance and case temperature. With the increasing case temperature, the value of thermal resistance became higher under each input power. Three factors affected the thermal performance including: the first, the relation between light output efficiency and junction temperature; the second, the effect of internal series electrical resistance Rin and external electrical resistance Rex; and the third, the materials degeneration of each part inside the LEDs package as the junction temperature increased. To combine the three factors could explain the thermal characteristics of high power LEDs.

Stacked Thermoelectric Generator Module Integrated with Partial Electric Conducted Interposer Structure

In this paper, we designed a new type of stacked thermoelectric generator (TEG) module integrated with partial electric conducted interposer (PECI) structure. The partial electric conducted interposer is assembled among the thermoelectric generator with 36 pairs of thermoelectric piles. The thermoelectric piles are made of P-type and N-type Bi2Te3 material with the thickness of 2 mm and the cross section area of 4 mm x 4 mm. The interposer is composed of low thermal conductivity material and partial distributed metal via, which leads to the characteristics of electrical conducted and highly thermal resisted. Results showed that under same heating power imported to the hot side of thermoelectric generator and same temperature controlled at the cold side, the temperature difference between these two sides performed a higher value of 13.6% in the interposing cases than that in conventional cases, and resulted in a higher output power of 10.6%.

Thermal performance of the IC package integrated with micro- thermoelectric device

The present work aims at the study of the cooling performance of a thermoelectric device that integrated with integrated heat spreader (IHS) on a flip-chip plastic ball grid array (FC-PBGA) package. The new thermoelectric device herein is fabricated on the metal substrates by flip-chip assembly process. Thermal performance of the new device was comprehensive studied. The thermal resistances of IHS with/without TEC were also compared. Moreover, a series of experiments have been carried out to investigate the effects of air velocity and the input power of thermoelectric device. The results showed that the new device that integrated with thermoelectric can reduce the thermal resistance of FC-PBGA package significantly.

Thermal Conductivity of Si/SiGe Superlattice Film

It has been proposed that the use of superlattice structure is effective for reduction of lattice thermal conductivity in the direction perpendicular to superlattice interfaces which can lead to improvement of figure of merit. In this work, we have evaluated the thermal conductivity of Si/SiGe superlattice structure films by theoretical analysis and experimental studies. In experiments, the ultra-high vacuum chemical vapor deposition (UHVCVD) has been employed to formation the Si/Si0.71 Ge0.29 superlattice film. The cross-plane thermal conductivity of a Si/Si0.71 Ge0.29 superlattice is measured based on the 3 ω method. In theoretical analysis, we use the Boltzmann transport equation to analyze the phenon transport in superlattice film. We compared the thermal conductivities of several Si/Si0.71 Ge0.29 superlattice structure films by changing the thickness of Si and Si0.71 Ge0.29 . The results indicate that increasing the period (one layer Si and one layer Si0.71 Ge0.29 ) length will lead to increase acoustic mismatch between the adjacent layers, and hence increased interfacial thermal resistance. However, if the total thickness of the superlattice film is fixed, reducing the period length will lead to decreased effective thermal conductivity due to the increased number of interfaces.© 2008 ASME

A thermoelectric cooler integrated with IHS on a FC-PBGA package

The present work aims at studying the cooling performance of a thermoelectric device that integrated with integrated heat spreader (IHS) on a flip-chip plastic ball grid array (FC-PBGA) package. The new thermoelectric device herein is fabricated on the metal substrates by flip-chip assembly process. Thermal performance of the new package was comprehensive studied. The thermal resistances of IHS with/without TEC were also compared. Moreover, a series of experiments have been carried out to investigate the effects of air velocity and the input current of thermoelectric device. The results showed that the integrated thermoelectric device can reduce the thermal resistance of FC-PBGA package significantly.

High Power LED Integrated With Silicon-Based Thermoelectric Cooler Package

A new thermal management application of silicon-based thermoelectric (TE) cooler integrated with high power light emitting diode (LED) is investigated in present study. The silicon-based TE cooler herein is fabricated by MEMS fabrication technology and flip-chip assembly process that is used for high power LED cooling. An electrical-thermal conversion method is used to estimate the junction temperature of LED. Moreover, the Integrating Sphere is also used to measure the light efficiency of LED. The thermal images photographed by infrared camera demonstrated the cooling function of the silicon-based TE devices. The results also show that high power LED integrated with silicon-based thermoelectric cooler package can effectively reduce the thermal resistance to zero. In addition, the light efficiency of the LED (1W) will increase under low TE cooler input power (0.55W), which is about 1.3 times of that without TE cooler packaging.Copyright