Electronic device cooling with autonomous fluid routing and method of assembly

An integrated circuit device is provided. The integrated circuit device includes a die having a first surface and a second surface opposite the first surface. The die has at least one circuit element positioned on its first surface. At least one micro-channel is defined in the second surface of the die. The integrated circuit device includes a cooling substrate attached to the second surface of the die. At least one fluid routing channel is defined in the cooling substrate. The at least one fluid routing channel is connected to the at least one micro-channel defined in the die. Additionally, the cooling substrate has at least one valve positioned within the at least one fluid routing channel. The at least one valve is configured to autonomously regulate a flow rate of a cooling fluid flowing through the at least one fluid routing channel.

BACKGROUND

The subject matter disclosed herein relates generally to cooling electronic devices and, more particularly, to methods and apparatus for dissipating heat from an integrated circuit device.

In at least some known electronic systems, e.g., computers, radios, radar modules, etc., the electronic device is the warmest component in the system. As such, at least some known electronic devices are coupled to a heat removal system to dissipate heat generated by the electronic device. Many known heat removal systems for such electronic devices include a path for heat flow with a high thermal resistance resulting in a high operating junction temperature. Generally, waste heat is removed by conduction, spreading, and convection to an appropriate cooling fluid with gradual reductions in temperature as the heat moves from the heat source to the cooling fluid. For example, the heat generated by a high-density power integrated circuit (“IC”) device may travel from the front side of the IC device trough the IC substrate, a thermal interface material, a heat spreader, and a heat sink before being transferred to a cooling fluid, e.g., air.

While considerable efforts have been made to develop heat removal systems that are reliable and efficient, these systems often only address the backside cooling of the electrical devices. In at least some known high-density power IC devices, e.g., IC amplifiers, the thermal resistance associated with the junction region on the front side of the IC die can be as large as the thermal resistance for the remaining components of the heat removal system. In at least some known IC devices, this junction region may typically include the first 100 microns of the IC device, often including an epitaxial layer of several microns coupled to a ceramic substrate, e.g., silicon, silicon carbide, etc.

BRIEF DESCRIPTION

In one aspect, an integrated circuit device is provided. The integrated circuit device includes a die with a first surface and a second surface opposite the first surface. The die includes at least one circuit element positioned on the first surface. The integrated circuit device also includes at least one micro-channel defined in the second surface of the die. Additionally, the integrated circuit device includes a cooling substrate attached to the second surface of the die. The cooling substrate includes at least one fluid routing channel connected to the at least one micro-channel, and at least one valve positioned within the at least one fluid routing channel. At least one valve is configured to autonomously regulate a flow rate of a cooling fluid flowing through the at least one fluid routing channel.

In another aspect, a cooling system for an integrated circuit device is provided. The cooling system includes at least one micro-channel defined in a die. In addition, the cooling system includes a cooling substrate attached to the die. The cooling substrate includes at least one fluid routing channel connected to the at least one micro-channel, and at least one temperature-responsive valve positioned within the at least one fluid routing channel. The at least one temperature-responsive valve is configured to autonomously regulate a flow rate of a cooling fluid flowing through the at least one fluid routing channel. Furthermore, the cooling system includes a fluid circulation pump fluidly attached to the at least one fluid routing channel. The fluid circulation pump is attached to the cooling substrate. The cooling system may also include a glass substrate attached to the cooling substrate, and a heat exchanger that includes at least one cooling channel fluidly connected to the at least one fluid routing channel and the fluid circulation pump. The heat exchanger may be attached to the glass substrate.

In another aspect, a method includes providing a die with a first surface and a second surface opposite the first surface. The die includes at least one circuit element positioned on the first surface. The method also includes forming at least one micro-channel in the second surface of the die to allow flow of a cooling fluid. The method includes coupling the die to a cooling substrate that has at least one fluid routing channel formed within the cooling substrate for receiving the cooling fluid. The method also includes coupling the die such that the at least one micro-channel is in flow communication with the at least one fluid routing channel. The method further includes positioning at least one temperature-responsive valve within the at least one fluid routing channel and configuring the at least one temperature-responsive valve to autonomously regulate the flow rate of the cooling fluid flowing through the at least one fluid routing channel.

DETAILED DESCRIPTION

The apparatus, systems, and methods described herein relate to cooling integrated circuit devices. A cooling module assembly includes a die with a plurality of micro-channels defined in a backside surface of the die. Additionally, the cooling module assembly includes a cooling substrate coupled to the backside of the die including an input manifold in fluid communication with a plurality of inlet channels, which are in fluid communication with the plurality of micro-channels, and an output manifold in fluid communication with the exit channels of the plurality of micro-channels. Furthermore, the cooling module assembly includes a heat exchanger in fluid communication with the output manifold, and a fluid circulation pump in fluid communication with the heat exchanger and the input manifold. One or more temperature-responsive valves are positioned within the exit channels of the plurality of micro-channels to regulate autonomously the flow rate of a cooling fluid flowing through the cooling module assembly. During operation, heat is transferred from the junction region of the die to the cooling fluid flowing through the micro-channels. The cooling fluid transfers the heat received from the junction region of the die to the heat exchanger then the cooling fluid is recirculated and pumped through the micro-channels in a hermetically sealed closed-loop autonomous cooling circuit.

Water is an effective cooling fluid because it provides a high convection heat transfer coefficient and a high specific heat. Water, however, is subject to freezing. In one embodiment, a mixture of ethylene-glycol and water or propylene-glycol and water, where the percentage of ethylene-glycol or propylene-glycol may be less than 60%, may be used because of the mixture's anti-freezing and corrosion inhibiting properties. In an alternative embodiment, a dielectric fluid may be used.

FIG. 1illustrates a perspective view of an exemplary integrated circuit device100including the cooling module assembly. Integrated circuit device100includes die112(also known as an IC die) including backside micro-channels (Shown inFIG. 2), cooling substrate102, fluid circulation pump104, heat exchanger106, glass substrate108, and valves110(also known as temperature-responsive valves) connected in a hermetically-sealed closed-loop autonomous cooling circuit. IC die112is coupled to cooling substrate102where its circuit elements are on the surface opposite cooling substrate102. As used herein, the term “die” or “IC die” refers to an object that affects electrons or their associated fields and generates heat as a by-product of its operation. Examples of IC dies include, but are limited to, semiconductors, microprocessors, digital signal processors, graphics processing units, diodes, transistors, or any other suitable heat-generating devices. In the exemplary embodiment, IC die112is a gallium nitride (“GaN”) high-electron mobility transistor device, including an epitaxial layer of several micrometers of GaN attached to a silicon carbide (“SiC”) substrate. Alternatively, IC die112may be any object that enables integrated circuit device100to function as described herein.

In the exemplary embodiment, a plurality of IC dies112are coupled to cooling substrate102to form integrated circuit device100. Any quantity of IC dies112, however, may be coupled to cooling substrate102that enables integrated circuit device100to function as described herein.

In the exemplary embodiment, cooling substrate102is coupled to IC die112using any suitable fastening mechanism that enables cooling substrate102or IC die112to function as described herein. For example, in the exemplary embodiment, cooling substrate102and IC die112are soldered together using a eutectic metal alloy, e.g., gold-tin (“Au—Sn”). In the exemplary embodiment, the use of the eutectic metal alloy enables cooling substrate102and IC die112to be coupled forming a hermetic seal therebetween. Alternatively, the solder material may include any suitable material or composition that enables cooling substrate102or IC die112to function as described herein.

To facilitate mitigating stresses resulting from thermal expansion between cooling substrate102and IC die112, in the exemplary embodiment, cooling substrate102may be fabricated from silicon, a material having a coefficient of thermal expansion (“CTE”) similar to that of the SiC substrate of IC die112. Alternatively, in another embodiment, cooling substrate102may be fabricated from copper alloys of molybdenum and tungsten, etc., or any other suitable material or composition that enables cooling substrate102and IC die112to function as described herein.

FIG. 2is a section view of the IC die112illustrating an end view of a plurality of backside micro-channels122. As shown, IC die112includes a plurality of circuit elements, or gates120on its front surface. Additionally, IC die112includes backside micro-channels122(described in detail below) for conducting the cooling fluid therethrough to absorb or dissipate heat generated at the junction region of IC die112by gates120. In the exemplary embodiment, micro-channels122terminate above respective inlet channels172and at respective fluid routing channels132as shown inFIGS. 3 and 6. Cooling substrate102is coupled to IC die112such that the cooling fluid entering micro-channels122is prevented from transferring to adjacent micro-channels122. A micro-channel, as that term is used herein, is a small groove or channel defined in the die substrate that functions to circulate, or channel, a cooling fluid therethrough. A micro-channel typically has at least one of its cross-sectional dimensions measuring less than 1 millimeter.

FIG. 3is an exploded section view of integrated circuit device100shown inFIG. 1. In the exemplary embodiment, cooling substrate102includes an input manifold130formed therein for channeling a cooling fluid from fluid circulation pump104to inlet channels172(Shown inFIG. 6). Inlet channels172circulate the cooling fluid to backside micro-channels122(Shown inFIG. 2) of IC die112. The heated cooling fluid is then channeled through a plurality of fluid routing channels132then through valves110which are positioned within fluid routing channels132(As shown inFIG. 1). After flowing through valves110, the cooling fluid is channeled to an output manifold (not shown) for passage to heat exchanger106.

Furthermore, in the exemplary embodiment, cooling substrate102defines pump cavity134. Defined within pump cavity134is pump inlet port136and pump outlet port138for channeling the cooling fluid through fluid circulation pump104(Shown inFIG. 1). Inlet check valve152is provided between inlet aperture144and pump cavity134and outlet check valve154is provided between pump cavity134and outlet aperture146.

As shown in the exemplary embodiment, glass substrate108includes an output port140for circulating the cooling fluid from the output manifold of cooling substrate102to heat exchanger106. As shown inFIG. 2, the cooling fluid is circulated through heat exchanger106via a plurality of cooling channels142formed in the top surface of heat exchanger106. However, heat exchanger106may use any configuration that enables heat exchanger106to function as described herein, including, but not limited to, offset strip fin or pin fin configurations. From heat exchanger106, the cooling fluid is circulated through inlet aperture144and routed to inlet check valve152and pump inlet port136. After passing through inlet check valve152and pump inlet port136, the cooling fluid is pressurized by fluid circulation pump104and circulated through pump outlet port138and outlet check valve154then through outlet aperture146to chamber148formed in the top surface of heat exchanger106. The cooling fluid is subsequently circulated to input manifold130through inlet port150.

In the exemplary embodiment, glass substrate108is coupled to cooling substrate102using any suitable fastening mechanism that enables glass substrate108and cooling substrate102to function as described herein. For example, in the exemplary embodiment, glass substrate108and cooling substrate102are bonded using anodic bonding, and are held together by an electrostatic field. In the exemplary embodiment, the use of anodic bonding enables glass substrate108and cooling substrate102to be coupled forming a hermetic seal therebetween. In another embodiment, glass substrate108and cooling substrate102are soldered together using a eutectic metal alloy, e.g., gold-tin (“Au—Sn”). In another embodiment, the solder material includes any suitable material or composition that enables glass substrate108and cooling substrate102to function as described herein.

In the exemplary embodiment, to facilitate mitigating stresses resulting from thermal expansion between glass substrate108and cooling substrate102and to facilitate the anodic bonding process, glass substrate108is fabricated from borosilicate glass. Borosilicate glass has a CTE similar to that of cooling substrate102, which in the exemplary embodiment is fabricated from silicon. In another embodiment, glass substrate108is fabricated from copper alloys of molybdenum and tungsten, etc., or any other suitable material or composition that enables glass substrate108and cooling substrate102to function as described herein.

Furthermore, in the exemplary embodiment, glass substrate108is coupled to heat exchanger106using any suitable fastening mechanism that enables glass substrate108and heat exchanger106to function as described herein. For example, in the exemplary embodiment, glass substrate108and heat exchanger106are bonded using anodic bonding to facilitate glass substrate108and heat exchanger106being coupled and having a hermetic seal formed therebetween. In another embodiment, glass substrate108and heat exchanger106are soldered together using a eutectic metal alloy, e.g., gold-tin (“Au—Sn”). In another embodiment, the solder material includes any suitable material or composition that enables glass substrate108and cooling substrate102to function as described herein.

In the exemplary embodiment, to facilitate mitigating stresses resulting from thermal expansion between glass substrate108and heat exchanger106and to facilitate the anodic bonding process, heat exchanger106is fabricated from silicon, a material having a CTE similar to that of glass substrate108. In another embodiment, heat exchanger106is fabricated from copper alloys of molybdenum and tungsten, etc., or any other suitable material or composition that enables glass substrate108and heat exchanger106to function as described herein.

FIG. 4illustrates a section view of integrated circuit device100shown inFIG. 1. In the exemplary embodiment, fluid circulation pump104is a piezoelectric diaphragm pump. However, fluid circulation pump104may be any type of pump that enables fluid circulation pump104to function as described herein. In the exemplary embodiment, fluid circulation pump104has a flow rate capability that ranges between 50 milliliters per minute (“ml/min”) and 200 ml/min and a pressure capability that ranges between 50 kilopascal (“kPa”), and 200 kPa.

In the exemplary embodiment, fluid circulation pump104is coupled to cooling substrate102using any suitable fastening mechanism that enables fluid circulation pump104and cooling substrate102to function as described herein. In one embodiment, the piezo component (not shown) is mounted to a metallic shim to form pump diaphragm160for fluid circulation pump104. Furthermore, pump diaphragm160is hermetically sealed in pump cavity134utilizing hermetic sealing methods including, but not limited to, soldering, brazing, welding, or glass frit bonding. In an embodiment where hermeticity is not necessary, an edge seal, including, but not limited to, a silicone, epoxy, or polymer edge seal, may be used to seal pump diaphragm160in pump cavity134, and to provide a reliable, high temperature, liquid seal that provides the flexure point for pump diaphragm160.

In one embodiment, pump inlet port136and pump outlet port138are defined within pump cavity134. Inlet check valve152is positioned between inlet aperture144and pump inlet port136where it allows the cooling fluid circulating from heat exchanger106to enter pump cavity134but does not allow the cooling fluid to exit pump cavity134through inlet check valve152. Outlet check valve154is positioned between pump outlet port138and outlet aperture146. Outlet check valve154allows the cooling fluid circulating from pump cavity134to enter chamber148but does not allow the cooling fluid to reverse flow and enter pump cavity134through outlet check valve154.

In the exemplary embodiment, an alternating current is provided to the piezo component (not shown), which vibrates pump diaphragm160and generates a pumping action. When pump diaphragm160is moving away from pump cavity134, inlet check valve152is opened and outlet check valve154is closed, so that the cooling fluid enters pump cavity134through pump inlet port136. Alternatively, when pump diaphragm160is moving toward pump cavity134, inlet check valve152is closed and outlet check valve154is opened, so that the cooling fluid exits pump cavity134through pump outlet port138.

Referring back toFIG. 2, micro-channels122have a substantially equal width “W” and a substantially equal distance “H” from gates120. Micro-channels122have a width “W” in the range between about 50 microns and about 175 microns. Additionally, micro-channels122have a distance “H” from gates120in the range between about 2 microns and about 60 microns. If micro-channels122are positioned too closely to the junction region of IC die112, the heat fluxes on the walls of micro-channel122will be very high locally below the gates120as shown inFIG. 6.

FIG. 5illustrates the heat flux distribution on the top surface of micro-channel122.FIG. 5shows that if micro-channel122is positioned at about 50 microns below the junction region of IC die112, the maximum heat flux values may be reduced to approximately one quarter the maximum heat flux value where micro-channel122is positioned at about 5 microns below the junction region. To prevent nucleation within the cooling fluid flowing through micro-channels122, it is preferred to keep heat flux values below 10 watts per square millimeter (“W/mm2”) at the micro-channel walls.

In the exemplary embodiment, each micro-channel122is configured to dissipate heat from two gates120of IC die112. In another embodiment, each micro-channel122is configured to dissipate heat from three gates120of IC die112. In another embodiment, each micro-channel122is configured to dissipate heat from four gates120of IC die112. However, micro-channels122may be configured to remove heat from any number of gates.

FIG. 6is a section view of the IC die112illustrating an edge view of a single backside micro-channel122. As described above, IC die112includes a plurality of gates120on its front surface. Micro-channels122are positioned below gates120with input edge170of micro-channels122substantially aligned with the edge of gates120. Micro-channels122have a substantially equal channel length “L.” Micro-channels122have a channel length “L” in the range between about 350 microns and about 600 microns. As shown, input manifold130, defined in cooling substrate102, defines a plurality of inlet channels172having an inlet width “B” for micro-channels122. Inlet width “B” has a range between about 40 microns and about 110 microns. Fluid routing channels132define the outlet width “C” for micro-channels122. In the exemplary embodiment, outlet width “C” may be oversized to reduce the pressure drop of the working fluid in the closed-loop system. Outlet width “C” has a range between about 100 microns and about 200 microns.

FIG. 7is a section view of integrated circuit device100illustrating the position of a valve110within a fluid routing channel132. The position of valves110is used to regulate autonomously the flow rate of the cooling fluid through fluid routing channels132. Valves110are coupled to cooling substrate102. As shown inFIGS. 3 and 7, valves110are positioned within fluid routing channels132and defined in a partially opened position for restricting the flow of the cooling fluid therethrough. The partially opened position of valves110is referred to as being the default partially opened curved position. One valve110is positioned in each fluid routing channel132. Although valves110inFIG. 3are all shown to be partially opened, each valve110alternatively expands or contracts independently of each other.

In the exemplary embodiment, valves110, also known as temperature-responsive valves, are fabricated from a shape memory alloy that senses a temperature difference in the cooling fluid and automatically opens or closes in response to the temperature difference. In one embodiment, temperature-responsive valves110are configured to open and close at specific temperatures depending on their design. Additionally, temperature-responsive valves110actuate without an additional control system, autonomously regulating the flow of the cooling fluid. In another embodiment, valves110are made of a temperature sensitive bi-material that senses a temperature difference and actuates in response to the temperature difference.

In operation, during normal conditions, temperature-responsive valves110are in their default partially opened curved position. However, as the temperature of the cooling fluid rises, temperature-responsive valves110actuate to regulate the amount of cooling fluid flowing through temperature-responsive valves110. In the exemplary embodiment, temperature-responsive valves110expand by straightening. In another embodiment, temperature-responsive valves110are configured to contract, further limiting the amount of cooling fluid circulating through temperature-responsive valves110.

In the exemplary embodiment, the autonomous cooling flow regulation in fluid routing channels132facilitates reducing hotspots in IC die112. Additionally, autonomous cooling flow regulation increases the reliability of integrated circuit device100by improving temperature uniformity and reducing thermal stresses. Furthermore, temperature-responsive valves110may prevent or reduce thermal runaway.

Exemplary embodiments of cooling integrated circuit devices are described above in detail. The apparatus, systems, and methods are not limited to the specific embodiments described herein, but rather, operations of the methods and components of the systems may be utilized independently and separately from other operations or components described herein. For example, the systems, methods, and apparatus described herein may have other industrial or consumer applications and are not limited to practice with electronic components as described herein. Rather, one or more embodiments may be implemented and utilized in connection with other industries.