Patent Application
20080268396
Microcircuits increasingly include a variety of disparate technologies. For example, considerable research is being conducted into the use of photonic interconnect for complementary metal-oxide-semiconductor (CMOS) digital circuits to overcome the limitations of metal-based interconnect. For example, silicon-based CMOS devices may be fabricated on a first wafer and indium-phosphide-based photonic devices fabricated on a second wafer. The first and second wafers are then bonded together to complete the microcircuit.
One significant difficulty in combining disparate technologies is the issue of heat management. For example, CMOS digital circuits can generate very high amounts of heat (e.g., 100 W/cm2). While CMOS is relatively insensitive to heat, it is necessary to remove heat from the microcircuit to avoid damage to the devices if too much heat is allowed to build up. Typically, heat removal has involved the attachment of the microcircuit to a heat sink of some type.
Some technologies, however, are very sensitive to heat. For example, photonic devices such as waveguides, resonators, transceivers, lattices, etc. can be very sensitive to small temperature changes (e.g., 0.1 degree C.). When heat-sensitive devices are placed in close proximity to heat-producing devices, the performance of the heat-sensitive devices may be compromised. Unfortunately, there is a desire to produce highly integrated microcircuits that combine disparate device types, and so it is not always possible to provide a separation between heat-sensitive and heat-producing devices. While heat sinks can help to remove heat from a microcircuit, any variations in the rate of heat production can result in variations in the temperature of the microcircuit, in turn affecting the operation of devices within the microcircuit.
Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
a) is side view illustration of a microcircuit having active temperature control in accordance with another embodiment of the present invention;
b) is a top view illustration of the microcircuit of
In describing embodiments of the present invention, the following terminology will be used.
The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a device” includes reference to one or more of such devices.
As used herein, the term “about” means that dimensions, sizes, formulations, parameters, shapes and other quantities and characteristics are not and need not be exact, but may be approximated and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like and other factors known to those of skill in the art.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
In view of the difficulties presented by integrating heat-producing devices and heat-sensitive devices into a microcircuit, it has been recognized by the present inventors that improved techniques for managing heat within a microcircuit are desirable. Accordingly, embodiments of the present invention include techniques for active temperature control within a microcircuit to allow compensation of spatially non-uniform and temporally-varying heat. For example, a plurality of temperature control elements can be included within the microcircuit and controlled to compensate for spatially non-uniform and temporally-varying heat emitted from heat-producing devices within the microcircuit. This can help to provide improved uniformity of temperature for heat-sensitive devices within the microchip.
One exemplary embodiment of the present invention is a microchip having active temperature control as illustrated in side view in
Also supported by the substrate 12 is a plurality of heat-sensitive devices 16 in proximity to the heat-producing electronic devices 14. The heat-sensitive devices may be in a different layer than the heat-producing electronic devices (as shown here), or the heat-sensitive electronic devices may be interspersed with the heat-producing electronic devices within a common layer as described further below. The heat-sensitive devices may be, for example, passive optical devices (e.g., add/drop filters, waveguides, etc.) or electro-optical devices (e.g., modulators, detectors, etc.) and combinations thereof.
A plurality of temperature control elements 18 are also supported by the substrate 12 and spatially distributed relative to the heat-producing electronic devices 14. The temperature control elements can be actively controlled to compensate for the spatially non-uniform and temporally-varying heat emitted from the heat-producing devices. For example, the temperature control elements can include a temperature sensor, a heating element, a cooling element, and multiples and combinations thereof. For example, thermistors, P-N semiconductor junctions, and the like can function as temperature sensors. As another example, a temperature sensor can be formed by measuring an output of a temperature-sensitive component. More particularly, a center frequency of a temperature-sensitive photonic transmitter can provide information regarding temperature of the photonic transmitter. Heating devices can include resistive heaters (e.g. wires formed from platinum, tantalum, or polysilicon), and combinations thereof. Cooling devices can include thermo electric coolers, and the like, and combinations thereof.
The microcircuit 10 may be fabricated, for example, as follows. The heat-producing electronic devices 14 and temperature control elements 18 may be fabricated on a first substrate (e.g. a silicon wafer). The heat-sensitive electronic devices 16 may be fabricated on a second substrate (e.g. a silicon on insulator wafer or a III-V semiconductor wafer). The first and second substrate may then be brought together and bonded together to form the microchip. If desired, the second substrate may be separated from the heat-sensitive devices after bonding to leave the heat-sensitive devices supported only by the first substrate.
Various arrangements of the heat-sensitive devices, heat-producing electronic devices, and temperature control elements are possible. For example,
In another embodiment, the microcircuit can include one or more heat-insulating layers to help distribute heat. For example,
Operation of a microchip with active temperature control will now be explained in further detail with reference to an exemplary embodiment illustrated in
When operated, the heat-producing CMOS devices 54 emit heat, which is conducted (in the Z direction) towards the heat-sensitive photonic devices 68, through the insulating layer 60 and (if present) electrical interconnect layers 70a, 70b. The heat is sensed by the temperature sensor 62. By including multiple temperature sensors, the spatial distribution of temperature within the microchip can be sensed. In particular, the temperature may vary horizontally (X and Y coordinates) over the heat-sensitive device layer 66. The output of the temperature sensor(s) 62 is provided to the feedback control circuitry 56, which can control the temperature control element(s) 64 to compensate for the time-varying spatial distribution of temperature. By including a distribution of temperature control elements over the heat-sensitive device layer, the spatial variation can be compensated for. The temperature control elements may be adjusted continuously using a feedback control loop to compensate for time variations. As another example, the temperature control elements may be adjusted periodically to compensate for time variations, for example, using a sampled time control loop (e.g., with a microprocessor or microcontroller performing calculations to close a feedback control loop).
If desired, control of the temperature control element(s) 64 can include predicting the time-varying spatial distribution of temperature. For example, where the microcircuit includes a microprocessor, based on the type of instructions being executed by the microprocessor, the heat generation that will occur may be predicted beforehand (for both time and space variations). Prediction of the heat generation may allow improved performance of the active temperature control.
Various feedback control loop algorithms including, for example, bang-bang, proportional, proportional-integral-derivative, and the like may be used. The feedback control loop 80 may include multiple feedback paths, for example, where temperature sensors 62 are included in locations near the heat-producing electronic devices and in locations near the heat-sensitive devices. A predictor algorithm 86 can accept inputs 88 such as, for example, electronics computation load information, to predict additional heating/cooling needs which are fed into the control algorithm.
With the temperature sensors(s) 62 positioned as shown in
The temperature control element(s) 64 can be also be positioned within either the heat-producing device layer 52, within the heat-sensitive device layer 66, or within both. As for the temperature sensor(s) 62, different performance may be obtained depending on where the temperature control elements are positioned. For example, by positioning the temperature control elements near the heat-producing devices, faster response to changes in the temporal or spatial characteristics of the heat may be obtained. On the other hand, positioning the temperature control elements near the heat-sensitive devices may provide for more accurate control in the temperature of the heat-sensitive devices. Which configuration will perform better will depend on the particular application characteristics. If desired, temperature sensors and temperature control elements may be included in a variety of locations and used within a multiple feedback loop control system.
For example,
Finally, a method of making a microchip having active temperature control is illustrated in flow chart form in
The method 100 may also include forming 106 a plurality of heat-sensitive devices supported by the substrate. For example, the heat-sensitive devices may be fabricated using photolithography. The heat-sensitive devices may be formed on top of, underneath, or within a common layer as the heat-producing electronic devices, for example as described above. The heat-sensitive devices may be formed on a separate wafer that is bonded to the substrate. The heat-sensitive devices may be photonic devices, as described above.
Another step of the method 100 can include forming 108 a plurality of temperature control elements spatially distributed relative to the heat-producing electronic devices and the heat-sensitive devices. The temperature control elements may be placed in various positions relative to heat-producing electronic devices and the heat-sensitive devices as described above. For example, the temperature control elements may be fabricated at the same time as the heat-sensitive devices, as described above.
It will be appreciated that the various fabrication steps can be performed in differing orders, including performing some steps simultaneously. Forming devices can be performing using photolithography as known in the art.
Summarizing and reiterating to some extent, a microcircuit having active temperature control in accordance with embodiments of the present invention can provide improved performance for heat-sensitive devices included within the microchip. Temporally and spatially varying heat flux produced by heat-producing devices within the microchip is sensed and compensated for via active control loops. Temperature sensing devices and temperature control devices can be distributed within the microchip as desired to provide temperature controlled regions within the microchip. Multiple regions having independent active temperature control systems can be implemented.
Active control of temperature with a microcircuit as described herein can enable temperature-sensitive devices, such as photonic components, to be used even when proximate to high heat-producing devices, such as CMOS devices. By maintaining a steady temperature for the temperature-sensitive devices, improved frequency stability, amplitude stability, and similar characteristics may be obtained.
While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
