Three-dimensional (3D) integrated circuits (ICs), which contain multiple layers of active devices, have the potential to dramatically enhance chip performance, functionality, and device packing density. They also provide for microchip architecture and may facilitate the integration of heterogeneous materials, devices, and signals. However, before these advantages can be realized, key technology challenges of 3D ICs must be addressed. More specifically, the processes required to build circuits with multiple layers of active devices must be compatible with current state-of-the-art silicon processing technology. These processes must also show manufacturability, i.e., reliability, good yield, maturity, and reasonable cost. To meet these requirements, IBM has introduced a scheme for building 3D ICs based on the layer transfer of functional circuits, and many process and design innovations have been implemented. This paper reviews the process steps and design aspects that were developed at IBM to enable the formation of stacked device layers. Details regarding an optimized layer transfer process are presented, including the descriptions of 1) a glass substrate process to enable through-wafer alignment; 2) oxide fusion bonding and wafer bow compensation methods for improved alignment tolerance during bonding; 3) and a single-damascene patterning and metallization method for the creation of high-aspect-ratio (6:1 108 vias/cm2), and extremely aggressive wafer-to-wafer alignment (submicron) capability.

Three-dimensional integrated circuits

Materials, technological status, and fundamentals of PEM fuel cells – A review

The purpose of this literature review is to compare different cooling technologies currently in development in research laboratories that are competing to solve the challenge of cooling the next generation of high heat flux computer chips. Today, most development efforts are focused on three technologies: liquid cooling in copper or silicon micro-geometry heat dissipation elements, impingement of liquid jets directly on the silicon surface of the chip, and two-phase flow boiling in copper heat dissipation elements or plates with numerous microchannels. The principal challenge is to dissipate the high heat fluxes (current objective is 300 W/cm2) while maintaining the chip temperature below the targeted temperature of 85°C, while of second importance is how to predict the heat transfer coefficients and pressure drops of the cooling process. In this study, the state of the art of these three technologies from recent experimental articles (since 2003) is analyzed and a comparison of the respective merits and ...

State of the Art of High Heat Flux Cooling Technologies

The depletion of the world's limited reservoirs of fossil fuels, the worldwide impact of global warming and the high cost of energy are among the primary issues driving a renewed interest in the capture and reuse of waste energy. A major source of waste energy is being created by data centers through the increasing demand for cloud based connectivity and performance. In fact, recent figures show that data centers are responsible for more than 2% of the US total electricity usage. Almost half of this power is used for cooling the electronics, creating a significant stream of waste heat. The difficulty associated with recovering and reusing this stream of waste heat is that the heat is of low quality. In this paper, the most promising methods and technologies for recovering data center low-grade waste heat in an effective and economically reasonable way are identified and discussed. A number of currently available and developmental low-grade waste heat recovery techniques including district/plant/water heating, absorption cooling, direct power generation (piezoelectric and thermoelectric), indirect power generation (steam and organic Rankine cycle), biomass co-location, and desalination/clean water are reviewed along with their operational requirements in order to assess the suitability and effectiveness of each technology for data center applications. Based on a comparison between data centers' operational thermodynamic conditions and the operational requirements of the discussed waste heat recovery techniques, absorption cooling and organic Rankine cycle are found to be among the most promising technologies for data center waste heat reuse.

A review of data center cooling technology, operating conditions and the corresponding low-grade waste heat recovery opportunities

To a large extent, scaling was not seriously challenged in the past. However, a closer look reveals that early signs of scaling limits were seen in high-performance devices in recent technology nodes. To obtain the projected performance gain of 30% per generation, device designers have been forced to relax the device subthreshold leakage continuously from one to several nA/µm for the 250-nm node to hundreds of nA/µm for the 65-nm node. Consequently, passive power density is now a significant portion of the power budget of a high-speed microprocessor. In this paper we discuss device and material options to improve device performance when conventional scaling is power-constrained. These options can be separated into three categories: improved short-channel behavior, improved current drive, and improved switching behavior. In the first category fall advanced dielectrics and multi-gate devices. The second category comprises mobility-enhancing measures through stress and substrate material alternatives. The third category focuses mainly on scaling of SOI body thickness to reduce capacitance. We do not provide details of the fabrication of these different device options or the manufacturing challenges that must be met. Rather, we discuss the fundamental scaling issues related to the various device options. We conclude with a brief discussion of the ultimate FET close to the fundamental silicon device limit.

Silicon CMOS devices beyond scaling

An enclosure apparatus provides for combined air and liquid cooling of rack mounted stacked electronic components. A heat exchanger is mounted on the side of the stacked electronics and air flows side to side within the enclosure, impelled by air-moving devices mounted behind the electronics. Auxiliary air-moving devices may be mounted within the enclosure to increase the air flow. In an alternative embodiment, air-to-liquid heat exchangers are provided across the front and back of the enclosure, and a closed air flow loop is created by a converging supply plenum, electronics drawers through which air is directed by air-moving devices, diverging return plenum, and a connecting duct in the bottom. In a variant of this embodiment, connecting ducts are in both top and bottom, and supply and return ducts are doubly convergent and doubly divergent, respectively. Auxiliary blowers may be added to increase total system air flow. The enclosure also may be provided with automatically opening vent panels to allow room air to circulate and cool in the event of an over-temperature condition. The design of the enclosure permits it to be constructed apart from the rack-mounted apparatus and subsequently attached to the rack, if desired, at the facility at which the rack had been previously operating.

Method and apparatus for combined air and liquid cooling of stacked electronics components

This paper provides a broad review of the cooling technologies for computer products from desktop computers to large servers. For many years cooling technology has played a key role in enabling and facilitating the packaging and performance improvements in each new generation of computers. The role of internal and external thermal resistance in module level cooling is discussed in terms of heat removal from chips and module and examples are cited. The use of air-cooled heat sinks and liquid-cooled cold plates to improve module cooling is addressed. Immersion cooling as a scheme to accommodate high heat flux at the chip level is also discussed. Cooling at the system level is discussed in terms of air, hybrid, liquid, and refrigeration-cooled systems. The growing problem of data center thermal management is also considered. The paper concludes with a discussion of future challenges related to computer cooling technology.

Review of cooling technologies for computer products

Augmenting air cooling of electronics systems using a cooling fluid to cool air entering the electronics system, and to remove a portion of the heat dissipated by the electronics. A cooled electronics system includes a frame, electronics drawers, fans or air moving devices, and an inlet heat exchanger. A cooling fluid such as chilled water is supplied to the inlet heat exchanger, to cool incoming air below ambient temperature. Fans cause ambient air to enter the system, flow through the inlet heat exchanger, through electronic devices, and exit the system. An optional exhaust heat exchanger further transfers heat dissipated by electronic devices to the cooling fluid. Heat exchangers are pivotally mounted, providing drawer access. Segmented heat exchangers provide access to individual drawers. Heat exchangers are integrated into cover assemblies. Airflow guides such as louvers are provided at inlets and outlets. Cover assemblies provide a degree of acoustic and electromagnetic shielding.

Method and system for cooling electronics racks using pre-cooled air

An apparatus is provided for facilitating cooling of an electronics rack. The apparatus includes a heat exchange assembly mounted to an outlet door cover hingedly affixed to an air outlet side of the rack. The heat exchange assembly includes a support frame, an air-to-liquid heat exchanger, and first and second perforated planar surfaces covering first and second main sides, respectively, of the air-to-liquid heat exchanger. The heat exchanger is supported by the support frame and includes inlet and outlet plenums disposed adjacent to the edge of the outlet door cover hingedly mounted to the rack. Each plenum is in fluid communication with a respective connect coupling, and the heat exchanger further includes multiple horizontally-oriented heat exchange tube sections each having serpentine cooling channel with an inlet and an outlet coupled to the inlet plenum and outlet plenum, respectively. Fins extend from the heat exchange tube sections.

Apparatus and method for facilitating cooling of an electronics rack employing a heat exchange assembly mounted to an outlet door cover of the electronics rack

A thermal dissipation assembly and method, and a cooled multi-drawer electronics rack are provided having a first cooling loop and a second cooling loop. The first cooling loop is disposed substantially within an electronics drawer and positioned to extract heat from an electronics module within the drawer. The first cooling loop further includes a first planar heat transfer surface. The second cooling loop is disposed substantially external to the electronics drawer and includes a second planar heat transfer surface. A biasing mechanism mechanically forces the first planar heat transfer surface and the second heat transfer surface coplanar when the electronics drawer is in a docked position in the electronics rack to facilitate the transfer of heat from the first cooling loop to the second cooling loop.

Michael J. Ellsworth

Papers

Method and apparatus for combined air and liquid cooling of stacked electronics components

Review of cooling technologies for computer products

Method and system for cooling electronics racks using pre-cooled air

Apparatus and method for facilitating cooling of an electronics rack employing a heat exchange assembly mounted to an outlet door cover of the electronics rack

Thermal dissipation assembly and fabrication method for electronics drawer of a multiple-drawer electronics rack