The number and density of electronic components in VLSI chips has sharply increased in modem ICs. The heat generated in the chip results in a high operating temperature if not removed, which will degrade both the responding speed the reliability of the electronic devices. A micro heat pipe is a promising cooling device to dissipate heat and to reduce the operating temperature....[ Read more ]

The number and density of electronic components in VLSI chips has sharply increased in modem ICs. The heat generated in the chip results in a high operating temperature if not removed, which will degrade both the responding speed the reliability of the electronic devices. A micro heat pipe is a promising cooling device to dissipate heat and to reduce the operating temperature.

The design, fabrication and characterization of an integrated micro heat pipe device are presented. The microdevice consists of a heater, an array of heat pipes, temperature and capacitive sensors. Taking advantage of the large difference between the dielectric constants of liquid and vapor, the integrated capacitor can be used for void-fraction measurements in two-phase flows. Both CMOS-compatible and glass-based fabrication technologies are reported. In the CMOS-compatible technology, the heat pipes are capped by a thin nitride layer utilizing wafer bonding and etch back technique. In the glass-based technology, the heat pipes are covered by a glass substrate using die-by-die anodic bonding to allow visualization of the two-phase flow patterns. This approach also results in a significant reduction of the parasitic capacitance, thus enhancing the sensitivity of the capacitance sensor. A few particular problems related to this technology are discussed and proper solutions are proposed.

The characterization of a micro heat pipe system is conducted. Two liquid charging schemes based on a single hole, requiring vacuum environment, and a pair of holes, utilizing capillary forces, are compared. Taking advantage of the great disparity between the dielectric constants of liquids and gases, capacitance sensors are used for void-fraction measurements. Since it is difficult to control the phase content of a liquid-gas mixture in a micro heat pipe, hence a calibration technique based on a traveling water-air interface due to evaporation is introduced. The integrated sensor capacitance for pure water is found to depend on measurement frequency, temperature and ion concentration, exhibiting trends different from previous reports. The measured temperature and void-fraction distribution along the heat pipes are consistent with the two-phase flow patterns recorded during the microsystem operation.