U.S. patent application number 12/242438 was filed with the patent office on 2009-11-12 for thermal control via adjustable thermal links.
Invention is credited to Alexandre Bratkovski, Theodore I. Kamins, Duncan Stewart.
Application Number | 20090277608 12/242438 |
Document ID | / |
Family ID | 41265922 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090277608 |
Kind Code |
A1 |
Kamins; Theodore I. ; et
al. |
November 12, 2009 |
Thermal Control Via Adjustable Thermal Links
Abstract
An apparatus for thermal control includes a first component; a
second component; an adjustable thermal link disposed between the
first component and the second component; and a controller for
selectively varying a thermal conductance of the adjustable thermal
link. A method of controlling a temperature includes sensing a
temperature of a first component; and adjusting a thermal
conductance of an adjustable thermal link, the adjustable thermal
link forming a thermal path between the first component and a
second component; the thermal conductance of the adjustable thermal
link being adjusted such that the temperature of the first
component is controlled.
Inventors: |
Kamins; Theodore I.; (Palo
Alto, CA) ; Stewart; Duncan; (Menlo Park, CA)
; Bratkovski; Alexandre; (Mountain View, CA) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY;Intellectual Property Administration
3404 E. Harmony Road, Mail Stop 35
FORT COLLINS
CO
80528
US
|
Family ID: |
41265922 |
Appl. No.: |
12/242438 |
Filed: |
September 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61051081 |
May 7, 2008 |
|
|
|
Current U.S.
Class: |
165/82 ; 165/61;
236/91D |
Current CPC
Class: |
F28F 2013/008 20130101;
F28F 13/00 20130101; F25D 19/006 20130101 |
Class at
Publication: |
165/82 ;
236/91.D; 165/61 |
International
Class: |
F28F 7/00 20060101
F28F007/00; F25B 29/00 20060101 F25B029/00 |
Claims
1. An apparatus for thermal control comprising: a first component;
a second component; an adjustable thermal link disposed between
said first component and said second component; and a controller
for selectively varying a thermal conductance of said adjustable
thermal link.
2. The apparatus of claim 1, wherein said adjustable thermal link
comprises particles within a compliant matrix.
3. The apparatus of claim 2, wherein said adjustable thermal link
comprises anisotropic particles suspended within a fluidic
matrix.
4. The apparatus of claim 1, wherein said adjustable thermal link
comprises alternating spacers and pliable layers, said spacers have
a substantially higher thermal conductivity than said pliable
layers, said spacers comprising a primary thermal path when said
adjustable thermal link is compressed.
5. The apparatus of claim 1, wherein said controller comprises a
piezoelectrically active element.
6. The apparatus of claim 1, wherein said controller comprises a
micro-electrical mechanical mechanism.
7. The apparatus of claim 1, wherein said controller applies an
electrical field or magnetic field across said adjustable thermal
link.
8. The apparatus of claim 1, wherein said controller comprises two
capacitive plates.
9. The apparatus of claim 1 wherein said controller comprises a
shape memory alloy.
10. The apparatus of claim 1 wherein said controller selectively
adjusts a dimension of said adjustable thermal link such that said
thermal conductance of said thermal link is altered.
11. The apparatus of claim 10, wherein compressing said adjustable
thermal link results in said thermal link having an increased
thermal conductance in at least one dimension.
12. An apparatus for thermal control comprising: a ring resonator;
a second component, said second component being a sub-chip level
electronic element; an adjustable thermal link between said ring
resonator and said second component, said adjustable thermal link
comprising a compressible matrix with embedded particles; and a
piezoelectrically active element; said piezoelectrically active
element altering dimensions in proportion to a bias voltage applied
across said piezoelectrically active element, said
piezoelectrically active element adjusting a dimension of said
adjustable thermal link such that thermal contact between said
embedded particles increases and thermal contact between said
embedded particles and surfaces of said ring resonator and said
second component increases, thereby increasing a thermal
conductance of said adjustable thermal link and controlling an
amount of thermal energy passing between said ring resonator and
said second component.
13. A method of controlling a temperature comprising: sensing a
temperature of a first component; and adjusting a thermal
conductance of an adjustable thermal link, said adjustable thermal
link forming a thermal path between said first component and a
second component; said thermal conductance of said adjustable
thermal link being adjusted such that said temperature of said
first component is controlled.
14. The method of claim 13, further comprising: quantifying a
desired shift in temperature of said first component; calculating
an electrical input; applying said electrical input to an actuation
means, said actuating means being configured to alter a dimension
of said adjustable thermal link such that a thermal conductance of
said adjustable thermal link is adjusted.
15. The method of claim 14, wherein: said actuation means comprises
a piezoelectrically active layer, said electrical input comprising
a voltage applied across said piezoelectrically active layer such
that said piezoelectrically active layer compresses said adjustable
thermal link; and said adjustable thermal link comprises a
compressible matrix with embedded particles.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from provisional
application Ser. No. 61/051,081, filed May 7, 2008, the contents of
which are incorporated herein by reference in their entirety.
BACKGROUND
[0002] Controlling the temperature of components within integrated
electronic systems can be challenging. Most electronic components
generate heat as a result of normal operation. This excess heat can
dissipate into surrounding components before leaving the
system.
[0003] Integrated electronic systems can have a number of
components that are temperature sensitive. For example, the
properties of resistors, diodes, transistors, and resonant
frequencies of oscillator crystals are all sensitive to
temperature. The physical dimensions, material stability, electron
behavior, chemical interactions, strength, and other properties are
also affected by temperature. In integrated electronic systems that
incorporate optical components, temperature variations can
adversely affect the ability of the optical components to generate,
modulate, and detect light.
[0004] As the integrated electronic system operates, it can produce
varying levels of heat that are proportional to the duty cycle of
various heat generating components. These changing heat loads can
cause undesirable temperature fluctuations within the system.
Consequently, temperature control and stabilization are major
design issues for integrated electronic systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The accompanying drawings illustrate various embodiments of
the principles described herein and are a part of the
specification. The illustrated embodiments are merely examples and
do not limit the scope of the claims.
[0006] FIG. 1 is a diagram showing one illustrative configuration
for applying an electric field to piezoelectric materials,
according to one embodiment of the principles described herein.
[0007] FIG. 2 is a diagram illustrating the response of
piezoelectric materials to an applied electric field, according to
one embodiment of the principles described herein.
[0008] FIG. 3 is a diagram of an illustrative ring resonator and
tangential waveguide, according to one embodiment of the principles
described herein.
[0009] FIGS. 4A and 4B are cross-sectional views of an illustrative
ring resonator, a heat source/sink, and an adjustable thermal link,
according to one embodiment of the principles described herein.
[0010] FIGS. 5A and 5B are cross-sectional diagrams showing an
illustrative adjustable thermal link, according to one embodiment
of the principles described herein.
[0011] FIGS. 6A and 6B are cross-sectional diagrams showing an
illustrative adjustable thermal link, according to one embodiment
of the principles described herein.
[0012] FIGS. 7A and 7B are cross-sectional diagrams showing an
illustrative adjustable thermal link, according to one embodiment
of the principles described herein.
[0013] FIGS. 8A and 8B are cross-sectional diagrams showing an
illustrative adjustable thermal link, according to one embodiment
of the principles described herein.
[0014] FIGS. 9A and 9B are cross-sectional diagrams of an apparatus
using an adjustable thermal link for temperature control, according
to one embodiment of the principles described herein.
[0015] FIGS. 10A and 10B are cross-sectional diagrams of an
apparatus using an adjustable thermal link for temperature control,
according to one embodiment of the principles described herein.
[0016] FIG. 11 is a cross-sectional diagram of an apparatus using
an adjustable thermal link for temperature control, according to
one embodiment of the principles described herein.
[0017] FIG. 12 is a cross-sectional diagram illustrating a
capacitive actuator to alter the thermal conductivity of an
adjustable thermal link, according to one embodiment of the
principles described herein.
[0018] FIGS. 13A and 13B are cross-sectional diagrams illustrating
a micro-electro mechanical mechanism to control the temperature of
a thermally sensitive component, according to one embodiment of the
principles described herein.
[0019] FIG. 14 is a flowchart showing one illustrative method of
utilizing an adjustable thermal link to control the temperature of
a component, according to one embodiment of the principles
described herein.
[0020] Throughout the drawings, identical reference numbers
designate similar, but not necessarily identical, elements.
DETAILED DESCRIPTION
[0021] Controlling the temperature of components within an
integrated electronic system can be challenging. Integrated
electronic systems can have a number of components that are
temperature sensitive. For example, resonant frequencies of
resonant system elements are very sensitive to temperature. The
physical dimensions, material stability, electron behavior,
chemical interactions, strength, and other properties of various
electronic components are affected by temperature. In integrated
electronic systems that incorporate optical components, temperature
variations can adversely affect the ability of the system to
generate, transmit, modulate and detect light.
[0022] As the integrated electronic system operates, it can produce
varying levels of heat that are proportional to the duty cycle of
various heat generating components. These changing heat loads can
cause undesirable temperature fluctuations within the system. For
example, in electro-optical systems that utilize ring resonators as
light sources, detectors, or modulators, the temperature of the
ring resonator directly affects its resonant optical frequency.
Significant changes in the resonant frequency of the ring resonator
can drastically alter the ring resonator's performance.
[0023] In compact designs, a variety of heat generating and heat
sensitive components can be in close proximity to each other. The
heat generated by one component can quickly and directly affect
adjacent components.
[0024] Methods of stabilizing the temperature within a system
include active methods of control, for example, using heaters to
raise the temperature of heat sensitive components above the
maximum temperature of surrounding components. Active methods
typically require additional power and introduce additional heat
into the system.
[0025] Passive methods of thermal control can also be used. For
example, components can be spaced out to minimize thermal cross
talk between components, a structure can be used to conduct heat
away from the components, or a specialized radiating surface can be
incorporated to dissipate heat. These methods can increase the
size, mass, and cost of the system. In many instances, passive
methods of thermal control lack the precision required for optimal
performance of thermally sensitive components.
[0026] As used in the specification and appended claims, the term
"thermal conductivity" refers to a material property that indicates
a homogeneous material's ability to conduct heat. More generally,
thermal conductivity can be used to describe the heat transferring
ability of a material or component through any internal means
including conduction, convection, radiation, or phase change. As
used in the specification and appended claims, the term "thermal
conductance" refers to the heat conducting ability of a structure
composed of various materials.
[0027] The current specification describes the use of an electrical
actuator to control the thermal conductance of an adjustable
thermal link between a first component and a second component. In
one embodiment, the first component may be a temperature-sensitive
component and the second component may be a heat source or sink.
The thermal conductance of the adjustable thermal link between the
temperature-sensitive component and the heat source/sink is
actively throttled to control the amount of heat flowing between
the components. By controlling the amount of heat entering a
temperature-sensitive component, its temperature can be controlled
or stabilized.
[0028] In an alternative embodiment, the adjustable thermal link
connects a heat source to a heat sink. The thermal conductance of
the adjustable thermal link is varied to maintain a constant
temperature at the heat source. For example, when the heat source
generates a large amount of heat, the thermal conductance of the
adjustable thermal link is increased so that the excess heat is
channeled through the adjustable thermal link and into the heat
sink. When the heat source is generating less heat, the thermal
conductance of the adjustable thermal link is reduced, decreasing
the amount of heat that is channeled into the heat sink. This
stabilizes the temperature of the heat source and reduces its
negative effects on surrounding components.
[0029] The concept of using an adjustable thermal link can be
applied to a wide variety of temperature control problems. For
purposes of explanation, optical ring resonators are used as one
specific example of a temperature-sensitive component. A number of
adjustable thermal link concepts are discussed, many of which
include piezoelectric or piezoelectrically active materials as
actuators which act on the thermal links. Piezoelectric materials
are materials whose shape can be altered by application of an
electric field across the material. Some examples of piezoelectric
materials are quartz and silicon. The speed of shape change in
response to a voltage across the piezoelectric material can be very
fast. Additionally, there is very little current flow through the
piezoelectric material; current flow would lead to power
consumption and heat dissipation.
[0030] As used in the specification and appended claims, the term
"controller" will be used generally to refer to the various
components that perform the function of altering or controlling the
thermal conductance of an adjustable thermal link. Thus, a
"controller" may include a piezo electric device, a voltage source,
an electric field generator, a micro-electrical mechanical system
(MEMS) and other components, examples of which are provided
below.
[0031] In the following description, for purposes of explanation,
numerous specific details are set forth in order to provide a
thorough understanding of the present systems and methods. It will
be apparent, however, to one skilled in the art that the present
systems and methods may be practiced without these specific
details. Reference in the specification to "an embodiment," "an
example" or similar language means that a particular feature,
structure, or characteristic described in connection with the
embodiment or example is included in at least that one embodiment,
but not necessarily in other embodiments. The various instances of
the phrase "in one embodiment" or similar phrases in various places
in the specification are not necessarily all referring to the same
embodiment.
[0032] FIG. 1 is an illustration of a circuit (100) shown to
demonstrate illustrative piezoelectric material qualities. A
piezoelectric material (105), which may be made of any material
that exhibits piezoelectric properties, is shown in series with a
voltage source (110) and a switch (115) in an open position.
[0033] The piezoelectric material (105) is sandwiched between two
plates (120, 121). The two plates (120, 121) are made of a
conductive or semiconducting material and are used to create an
electric field across the piezoelectric material (105). Because the
switch (115) is open, there is no applied voltage differential
across the plates (120, 121) and therefore no electric field across
the piezoelectric material (105). The piezoelectric material's
dimensions (106, 107, 108) are the dimensions of the piezoelectric
material (105) in its natural or unaltered state. As will be
apparent to one skilled in the art, the actual shape and geometry
of the piezoelectric material can vary greatly as best suits a
particular application.
[0034] FIG. 2 represents the same circuit (100) and piezoelectric
material (105) except that the switch (115) is in its closed
position. Because the switch (115) position is closed, the voltage
source (110) is able to apply a voltage difference to the plates
(120, 121) creating an electric field across the piezoelectric
material (105). The piezoelectric properties of the piezoelectric
material (105), responding to the applied voltage bias from the
voltage source (110), result in a change in the physical geometry
of the piezoelectric material (105). The physical change of the
piezoelectric material is apparent in the new dimensions (206, 207,
208) of the piezoelectric material (105).
[0035] The changes between the dimensions (106, 107, 108) of the
piezoelectric material (105) in FIG. 1 and the dimensions (206,
207, 208) of the piezoelectric material (105) in FIG. 2 are greatly
exaggerated for illustrative purposes. The actual changes in the
dimensions of a piezoelectric material in response to an applied
voltage or electric field are usually much less dramatic and
dependent on the type of piezoelectric material used, the unbiased
or natural geometry of the piezoelectric material, and the
magnitude and distribution of the electric field applied across the
piezoelectric material.
[0036] FIG. 3 is a diagram of an illustrative optical modulator
(300). The illustrative optical modulator (300) has a first optical
waveguide or "ring resonator" (301) arranged in a loop. A second
"tangential" optical waveguide (303) is tangentially arranged with
respect to the first optical waveguide (301) and is optically
coupled to the ring resonator (301). The ring resonator (301) and
tangential waveguide (303) are in optical communication with each
other near the point where the tangential waveguide (303) passes
closest to the ring resonator (301).
[0037] A heat generating electrical component (311) is shown
adjacent to the ring resonator (301). In other situations, the heat
generating electrical component may be under the optical structure
rather than coplanar with the optical structure.
[0038] In some cases, it can be desirable for the optical resonant
frequency of the ring resonator (301) to substantially match the
optical frequency of a portion of energy passing through the
tangential waveguide (303). For example, in wavelength division
multiplexing, the optical energy transmitted through the tangential
waveguide can be made up of optical energy divided among a
plurality of different wavelength bands or "lines." Each line may
be narrow, on the order of 1 MHz to 1 GHz in width. Each different
line can serve as a carrier signal for a separate data signal.
[0039] Ring resonators (301) that are optically coupled to the
tangential waveguide (303) can be tuned to specific lines for
modulation, detection, and de-multiplexing operations. The ring
resonator (301) has a resonant frequency which is at least
partially determined by its geometry and operating temperature. The
ring resonator (301) is configured to sustain optical energy having
a wavelength corresponding to the resonant frequency or a range of
wavelengths centered on the resonant frequency of the resonator
(301). Other optical energy of any different wavelength is
attenuated or suppressed within the ring resonator (301) by
destructive interference.
[0040] Changes in the operating environment can cause the resonant
frequency of a ring resonator to undesirably shift away from the
line frequency that the ring resonator is paired with. For example,
when the adjacent electrical component (311) is heavily utilized
and generates a large amount of thermal energy, the thermal energy
is transferred to the surrounding components. In this case, the
thermal energy will be partially absorbed by the ring resonator
(301) and tangential wave guide (303).
[0041] The internal temperature of the ring resonator (301) rises
proportionally to the amount of thermal energy it absorbs.
Increases in the internal temperature of the ring resonator (301)
may cause dimensional and optical changes which alter the resonant
optical frequency of the ring resonator (301). Thus, as the duty
cycle of the adjacent electrical component (311) changes, the
temperature of the ring resonator (301) may also change and
adversely affects its performance.
[0042] Thermal control and stabilization of the ring resonator
(301) can be desirable to limit the thermal variations within the
system. Additionally, it can be desirable to shift the optical
resonant frequency of a ring resonator (301) from one line to
another. By actively controlling one or more factors that affect
the ring's optical resonant frequency, the ring (301) can be
"tuned" to keep its optical frequency aligned with a given line or
switch from one line to another.
[0043] In one method of controlling or stabilizing the temperature
of a ring resonator (301), a heating element is incorporated into
the design that is controlled to obtain the desired temperature and
therefore the desired resonant frequency of the ring resonator. The
stabilized temperature is typically higher than the maximum
operating temperature of the surrounding components. However,
because of the inclusion of heating elements, a greater amount of
power and heat dissipation occurs within the system. Further, in
high density applications, thermal cross talk between different
heated ring resonators can become a problem. In applications where
lower heat dissipation and high component densities are desired,
alternative methods of tuning the ring resonators can be used.
[0044] Optical energy is generated by an optical source (307), such
as a laser or a light emitting diode (LED), and enters the
modulator (300) through a first end of the tangential optical
waveguide (303). The optical energy is then transmitted through the
optical coupling between the tangential waveguide (303) and the
ring resonator (301) into the ring resonator (301). As noted above,
optical energy having the correct wavelength (i.e. at or near the
resonant frequency of the ring resonator(301)) will be sustained by
the resonator (301), while optical energy at other wavelengths will
be suppressed by destructive interference.
[0045] A wavelength that is being used to transmit data between the
optical source (307) and an optical receiver (309) may be referred
to as the carrier wavelength. The carrier wavelength may or may not
correspond to the resonant frequency of the ring (301) depending on
how the modulator (300) is configured to perform.
[0046] For example, the ring resonator (301) may act as a modulator
of the carrier wavelength by selectively varying the amount of
coupling between the ring resonator (301) and the tangential
waveguide (303) or the amount of absorption of the carrier
wavelength within the ring resonator (301) by detuning the resonant
frequency of the ring (301) away from the carrier wavelength. The
modulated optical energy may then be transmitted through the
remainder of the tangential optical waveguide (303) to the optical
receiver (309) disposed at a second end of the tangential optical
waveguide (303). The receiver (309) may be, for example, a
photodetector or another waveguide.
[0047] FIGS. 4A and 4B are cross-sectional views of an illustrative
ring resonator (402, 410, 412), a heat source/sink (404), and an
adjustable thermal link (414). According to one exemplary
embodiment, the ring resonator (402, 410, 412) and heat source/sink
(404) are supported by a substrate (406). Above the substrate
(406), an insulating layer (408) electrically isolates the
components from the substrate (406). The ring resonator (402, 410,
412) is comprised of a core (402) and surrounding electrodes (410,
412). As discussed above, the core (402) is optically transparent
over a range of optical energy which passes through it. The
electrodes (410, 412) are configured to inject charge carriers into
the core (402), thereby influencing the optical energy that passes
through the core (402).
[0048] According to one embodiment, the heat source/sink (404)
shares a common support with the ring resonator (402) and is placed
on the insulating layer (408). In alternative embodiments, the heat
source/sink (404) may be located under or above the ring resonator
(402) rather than coplanar with the ring resonator (402). The heat
source/sink (404) may represent a variety of electrical or other
components. By way of example and not limitation, the heat
source/sink (404) may be a resistor, capacitor, memory chip,
processor, light emitting diode, detector, cooling fin, heat pipe,
etc. When the heat source/sink (404) is a heat sink, it may
represent a radiator, large surface area conductor, passive
electrical component, or other element capable of dissipating heat
absorbed from surrounding components.
[0049] An adjustable thermal link (414) is placed above the core
(402) and the heat source/sink (404). According to one exemplary
embodiment, the adjustable thermal link (414) is in thermal contact
with the upper surface of the core (402) and the upper surface of
the heat source/sink (404). Above the adjustable thermal link (414)
is a piezo active layer (416) and a restraining layer (420). The
piezo active layer (416) is sandwiched between the adjustable
thermal link (414) and the restraining layer (420) such that the
expansion of the piezo active layer (416) compresses the adjustable
thermal link (414).
[0050] According to one exemplary embodiment, the adjustable
thermal link (414) has a low thermal conductivity in an
uncompressed state and a high thermal conductivity in a compressed
state. In FIG. 4A, the piezoelectrically active layer (416) is in a
relaxed state and the adjustable thermal link (414) is in a low
thermal conductivity state. The adjustable thermal link (414) may
be comprised of a variety of materials in a variety of
configurations. According to one exemplary embodiment, the
adjustable thermal link (414) is comprised of a compressible matrix
(422) in which a number of thermally conductive particles (424) are
embedded. In the embodiment illustrated in FIG. 4, the thermally
conductive particles (424) are randomly oriented and distributed
throughout the matrix (422).
[0051] FIG. 4B shows the adjustable thermal link (414) in a
compressed state. To compress the adjustable thermal link (414), a
voltage difference is applied across the electrodes (120, 121; FIG.
1), which causes the piezoelectrically active layer (416) to alter
its dimensions, thereby compressing the adjustable thermal link
(414). As the adjustable thermal link (414) is squeezed between the
piezo active layer (416) and the upper surface of the core (402)
and the upper surface heat source/sink (404), the matrix (422) is
compressed and deformed. The compression and deformation of the
matrix (422) allows the thermally conductive particles (424) to
come into closer contact with each other and with the surface of
the components (402, 404). The thermal contact conductance between
the coupling layer (414) and the components (402, 404) is also
increased because of higher contact pressure and increased contact
surface area. This creates a more thermally conductive path through
the thermal coupling layer (414) which allows heat to flow between
the two components (402, 404) at a greater rate.
[0052] It will be recognized that a variety of factors may
influence the rate at which heat flows between the two components
(402, 404). By way of example and not limitation, these factors may
include the relative temperature differential between the two
components (402, 404), the thermal conductivity of the components
(402, 404), the amount of compression exerted by the piezo active
layer (416), the thermal conductance of the adjustable thermal link
(414), the surface contact resistance between the adjustable
thermal link (414) and the component, the geometry and thermal
conductivity the particles (424), the thermal conductivity of the
matrix (122), and other factors.
[0053] By varying the voltage differential across the
piezoelectrically active layer (416) the compression of the
adjustable thermal link (414) is altered, thereby changing the
thermal conductance. The temperatures of the various components
(402, 404) are dependent on the incoming heat flux, outgoing heat
flux, and heat generated within the component itself. In the
embodiment shown in FIGS. 4A and 4B, the temperature of the
components (402, 404) is controlled/stabilized by controlling the
amount of heat flux which flows between the two components. For
example, when the heat source/sink (404) is a heat generating
component and the ring resonator (402) is a thermally passive
element, the heat source (404) may have a significantly higher
temperature than the ring resonator (402). In many electronic
devices that generate a significant amount of heat, the heat
generated is directly dependent on the usage or duty cycle of the
component (404). As the usage of the component (404) increases, the
amount of heat generated within the component also changes. Without
the adjustable thermal link (414) and active piezoelectric layer
(416), the heat from the heat source (404) would pass through the
substrate (406) and insulating layer (408) and into the ring
resonator (402, 410, 412). As the heat generated from the component
varied over time, the temperature of the ring resonator would also
vary. As described above, variations in temperature of a ring
resonator (402, 410, 412) can be detrimental to its
performance.
[0054] With the addition of the adjustable thermal link (414) and a
means for actuating the adjustable thermal link (414), the
temperature of the ring resonator (402, 410, 412) can be stabilized
by varying the amount of heat that passes through the adjustable
thermal link (414). When the heat generating component (404)
generates less heat, the piezoelectrically active layer (416) could
compress the adjustable thermal link (414) and allow a greater
portion of the heat generated by heat source (404) to pass into the
ring resonator (402). When the heat source (404) generates more
heat, the piezo active layer 416) is relaxed and the thermal
conductance of the adjustable thermal link (414) is reduced,
thereby allowing less thermal energy to pass through the adjustable
thermal link (414) into the ring resonator (402). In this manner,
the temperature of the ring resonator (402) can be stabilized over
wide variety of operating conditions.
[0055] According to one exemplary embodiment, a temperature sensor
in proximity to the ring resonator (402) and/or heat source (404)
may sense the temperature and provide information, allowing the
desired voltage differential across the piezoelectrically active
layer (416) to be calculated. The temperature of the ring resonator
(402) may also be indirectly determined in a variety of ways
including sensing the optical resonant frequency of the ring
resonator (402).
[0056] FIGS. 5A and 5B are cross-sectional diagrams showing an
illustrative embodiment of an adjustable thermal link (500).
According to this exemplary embodiment, changes in the contact area
(506) between an upper subelement (504) and a lower subelement
(502) change the amount of heat which flows between the two
surfaces. In the example shown in FIGS. 5A and 5B, the subelements
are shown as having regular saw tooth profile. In the uncompressed
state shown in FIG. 5A, only small portions near the tips of the
upper and lower sawtooth profiles are touching. The contact areas
(506) serve as the only conduction path between the two surfaces.
In the compressed state shown in FIG. 5B, the contact area is
significantly increased, thereby increasing the overall thermal
conductance through the adjustable thermal link (500).
[0057] According to one exemplary embodiment, other modes of heat
transfer are minimized within the adjustable thermal link (500). By
way of example and not limitation, upper and lower surface may be
polished to reduce radiative heat transfer. The size of the teeth
could be chosen to reduce the convection in the air pockets between
the teeth. In one embodiment, compressible solid insulating
material could be used to displace the air in the voids between the
teeth.
[0058] FIGS. 6A and 6B are cross-sectional diagrams showing an
illustrative embodiment of an adjustable thermal link (600). In
some circumstances, the shape and orientation of particles (604)
within the adjustable thermal link may be selected to increase the
variation in thermal conductance when the compressible layer (610)
is compressed.
[0059] FIG. 6A shows the adjustable thermal link (600) in an
uncompressed state. Similar to the embodiment shown in FIGS. 4A and
4B, a number of thermally conducting particles (604) are embedded
in a compressible matrix (602). In this illustrative embodiment,
the particles (604) are substantially similar in geometry and are
positioned within the matrix in a regular periodic orientation. In
one exemplary embodiment, the particles (604) may exhibit a higher
thermal conductivity while the matrix (602) has a lower thermal
conductivity. The orientation and repeating pattern of the
particles within the matrix is only one example of the particles'
orientations and patterns which could be used to change the thermal
conductance of the adjustable thermal link when a dimension is
altered.
[0060] In an uncompressed state, the adjustable thermal link (600)
has low thermal conductance through its thickness and along its
length. The thermally conductive particles (604) have little
contact with the upper component (608), the lower component (606)
or with each other. Consequently, heat which enters a thermally
conductive particle (604) must follow a contorted path to travel
either horizontally or vertically through the compressible layer
(610).
[0061] FIG. 6B shows the adjustable thermal link (600) in its
compressed state. In its compressed state, the upper component
(608) and a lower component (606) are brought closer together,
thereby compressing the compressible layer 610). As the
compressible layer (610) is compressed, the particles (604) are
re-oriented and become interlocked with the adjoining rows of
particles. Additionally, the surface contact area between the
particles and the component surfaces is substantially increased by
bringing the longitudinal sides into contact with the upper and
lower surfaces. Heat can then pass relatively easily between and
within the two components (608, 606) in both vertical and
horizontal paths, respectively. Heat passing vertically from one
component to another allows an equalization of temperatures between
two components (608, 606). The ability of heat to pass horizontally
through the adjustable thermal link (610) minimizes temperature
variations within the individual components and allows for more
uniform heat flux between the two components (608, 606).
[0062] FIGS. 7A and 7B are cross-sectional diagrams showing an
adjustable thermal link (704) interposed between a heat-generating
component (710) and a temperature-sensitive component (702). In
this embodiment, the heat-generating component (710) is on the
bottom of the assembly. The heat-generating component (710) may
represent the upper surface of an integrated circuit that has
internal electronic elements which generate heat. The
temperature-sensitive component (702) is placed on top of an
adjustable thermal link (704). In alternative embodiments, the
adjustable thermal link (704) can be above the
temperature-sensitive component (702) and connect it to a heat
sink.
[0063] According to one exemplary embodiment, the adjustable
thermal link (704) may be comprised of a liquid or semi liquid
matrix (706) with a number of suspended particles (708). In one
embodiment, the liquid or semi liquid matrix (706) has a low
thermal conductivity, while the particles have a higher thermal
conductivity (708). In FIG. 7A the suspended particles (708) are
shown in an at-rest state, with the majority of the particles
having their major axis perpendicular to the heat path from the
heat-generating component (710) to the temperature-sensitive
component (702). This represents a minimally conductive state. The
thermal energy passing from the heat-generating component (710)
must pass into the liquid (706) and across the width of a particle
(708) and back into the liquid many times before reaching the
temperature-sensitive component (702).
[0064] FIG. 7B represents the adjustable thermal link (704) in a
more highly conductive state. According to one exemplary
embodiment, the particles (708) are reoriented under the influence
of charges (716, 714) which have been introduced onto the surfaces
surrounding the thermal coupling layer (704) by an applied voltage
source (712). The particles (708) have been reoriented so that
their major axes are parallel to the heat path. Thermal energy
passing from the heat-generating component (710) into the
temperature-sensitive component (702) will only have to pass
through a minimal amount of liquid (706) before entering a particle
(708) and being conducted down its major axis. By reducing the
number of particle/liquid interfaces through which the heat must
pass and maximizing the portion of the heat path that extends
through the major axis of the particles (708), the overall thermal
conductance of the adjustable thermal link (704) is increased.
[0065] This embodiment has a number of advantages. For example, the
voltage may be varied in an analog manner to selectively throttle
the flow of heat into the temperature-sensitive component (702).
This allows for more precise control of the temperature of the
various components. When the adjustable thermal link is an
electrical insulator, the charges (714, 716) are trapped in a
situation that is analogous to a capacitor. This capacitive
charging of the surfaces surrounding the adjustable thermal link
(704) reduces the power consumption and heat generation of the
adjustable thermal link (704).
[0066] FIGS. 8A and 8B are cross-sectional diagrams showing an
illustrative adjustable thermal link (800). In this exemplary
embodiment, the adjustable thermal link (800) is comprised of a
number of spacers (604) and a number of pliable layers (802). As
shown in FIG. 8A, the adjustable thermal link (800) in an
uncompressed state exhibits a relatively low thermal conductance
between an upper component (808) and a lower component (806).
According to one exemplary embodiment, the spacers (804) have a
high thermal conductivity while the pliable layers (802) have a
lower thermal conductivity. The lowest row of spacers is in direct
contact with the lower component (806). For heat to travel from the
lower component (806) to the upper component (808) the heat must
pass from a lower spacer into a first pliable layer, horizontally
along the first pliable layer into a second spacer, from the second
spacer into a second pliable layer, along the second pliable layer
into a third spacer and so forth until the heat reaches the second
component (808). This contorted path provides high thermal
resistance and results in only a minimal amount of thermal energy
passing between the upper component (808) and the lower component
(806).
[0067] FIG. 8B shows the adjustable thermal link (800) in its
compressed state. In its compressed state, the adjustable thermal
link (800) creates direct thermal paths between the lower component
(806) and the upper component (808). When compressed, the pliable
layers (802) are deformed, allowing spacers (804) to be pressed
vertically together. The compressed spacers form a column that
provides a direct thermal path between the two components (808,
806). Additionally, the spacers (804) are pressed against the
surfaces of the upper component (808) and lower component (806).
This reduces the surface contact resistance and allows heat to flow
more easily into the spacers (804). The thermal energy may then
pass directly into a spacer, through the thicknesses of the pliable
layers (802) that separate the first spacer from the second spacer
and so forth and until the heat passes into the other
component.
[0068] According to one exemplary embodiment, a piezoelectrically
active layer (e.g. 416, FIG. 4) may provide the compressive force
required to change the thermal conductance of the thermal coupling
layer (800). In an alternative embodiment, the pliable layers (802)
may be deformed by other means. By way of example and not
limitation, the pliable layers (802) may be made out of a
temperature-sensitive material, such as a memory alloy. When the
temperature of the component or components rises above a transition
temperature, the memory alloy layers (802) return to their original
serpentine shape and bring the two components (808, 806) together.
The use of memory alloy pliable layers (802) allows for passive
control of the component temperatures and may reduce the complexity
of the control system.
[0069] In an alternative embodiment, the electricity may be passed
through the memory alloy pliable layers (802) causing their
temperature to rise above the transition temperature and return to
their original serpentine shape, thereby increasing the thermal
conductance between the two components. In other embodiments, the
spacers (804) may be thermal insulators and the layers (802) may
have a high thermal conductivity. For example, the spacers (804)
could have an open cell structure while the layers (802) are
resilient metal foil.
[0070] The examples of adjustable thermal links given in FIGS. 4,
5, 6, 7, and 8 are examples of possible adjustable thermal links
that exhibit a change in thermal conductance in response to a
dimensional change or a reorientation of embedded elements. A
variety of other embodiments could be used. By way of example and
not limitation, magnetic particles could be reoriented within a
matrix in response to an applied magnetic or electrical field. In
an alternative embodiment, the adjustable thermal link could be
comprised of a number of high thermal conductivity fibers embedded
in a matrix. For example, carbon nanotubes exhibit high thermal
conductivity along their long dimension and relatively low
transverse thermal conductivity between adjacent carbon nanotubes.
By pressing a bundle of carbon nanotubes between two surfaces, the
heat could enter the nanotubes through the large transverse area
and be carried longitudinally away from the component.
[0071] In an alternative embodiment, a doped semiconductor could be
used as an adjustable thermal link. For example, some dopant ions
move through the semiconductor lattice at room temperature in
response to an applied electrical field. For example, lithium ions
can move through a silicon lattice. The dopant atoms change the
electrical and thermal conductivity of the bulk semiconductor
material through which they move. Therefore, moving dopant atoms
part way or all the way through the adjustable thermal link will
increase its thermal conductance and the thermal communication
between the components on either side of the adjustable thermal
link. One advantage of this embodiment is that the bulk
semiconductor material and dopant atoms can be deposited and formed
through standard integrated-circuit techniques. Additionally,
because the ions make up only a small portion of the lattice
material, changes in the dimensions of the adjustable thermal link
would be negligible. This allows the adjustable thermal link to
provide a stable base upon which a temperature-sensitive component
could be formed.
[0072] In many embodiments, a large number of air pockets are
present in the uncompressed state of the adjustable thermal link.
These small pockets of air provide a high level of thermal
isolation between the two components. As the adjustable thermal
link is compressed, the air pockets collapse and expel the air.
This can lead to a much higher thermal conductance of the
adjustable thermal link.
[0073] FIGS. 9, 10, 11, 12, and 13 illustrate various
configurations and actuation methods for controlling the
temperature of a component or components using an adjustable
thermal link.
[0074] FIGS. 9A and 9B are cross-sectional diagrams of an apparatus
(900) using an adjustable thermal link (906) to control
temperature. The first component (912) and the second component
(904) are supported by a common base (902). A piezoelectrically
active layer (908) and an adjustable thermal link (906) are placed
in the gap between the first component (912) and the second
component (904). An upper restraining layer (910) prevents the
upward motion of the piezoelectrically active layer (908).
[0075] FIG. 9A shows the adjustable thermal link (906) in an
uncompressed state. In the uncompressed state, the voltage across
the piezoelectrically active layer (908) is minimal and the
piezoelectrically active layer (908) is not extended. As previously
discussed, the adjustable thermal link (906) may take a variety of
forms. In FIG. 9A, the adjustable thermal link (906) is comprised
of a matrix with a number of randomly oriented particles.
[0076] FIG. 9B illustrates the compression of the adjustable
thermal link (906) by the piezoelectrically active layer (908). As
previously discussed, the piezoelectrically active layer (908) may
be extended or compressed by applying a voltage across the
electrodes (120, 121; FIG. 1). The voltage difference across the
electrodes (120, 121; FIG. 1) may be selected to obtain the desired
level of compression in the adjustable thermal link (906). Higher
voltage differences across the electrodes results in greater
extension of the piezoelectrically active layer (908) and
correspondingly greater compression of the adjustable thermal link
(906). As the adjustable thermal link (906) is compressed, the
matrix collapses and brings the particles into closer contact with
both each other and the surfaces of the joining components. In this
exemplary embodiment, the extension of the piezoelectrically active
layer (908) and resulting compression of the adjustable thermal
link (906) have been exaggerated for illustration purposes.
However, even small changes in displacement can greatly contribute
to controlling the temperature of system components.
[0077] The thermal conductance between the first component (912)
and the second component (904) is also increased by the reduction
in surface contact resistance between the adjustable thermal link
(906) and surrounding components (902, 904, 912) and the increase
in surface contact area as the adjustable thermal link is deformed
and pressed against greater portions of surrounding surfaces. As
was previously mentioned, the conducting particles also come in
greater contact with each other, thereby increasing the internal
thermal conductance of the thermal coupling layer (906).
[0078] FIGS. 10A and 10B are cross-sectional diagrams of an
apparatus (1000) using an adjustable thermal link (1006). A base
(1002) provides support and structure for the apparatus (1000).
According to one exemplary embodiment, a first component (1010) is
rigidly affixed to the base (1002). A second component (1004)
slidably interfaces with the base (1002). A piezoelectrically
active layer (1008) is rigidly restrained at one end by the base
(1002) and presses against the second component (1004) at the other
end. Interposed between the first component (1010) and the second
component (1004) is an adjustable thermal link (1006). In this
exemplary embodiment, the adjustable thermal link (1006) has a
configuration similar to the adjustable thermal link (800)
illustrated in FIG. 8. However, any one of a number of adjustable
thermal link configurations could be used.
[0079] In FIG. 10A, the adjustable thermal link (1006) is
illustrated in an uncompressed state. The adjustable thermal link
(1006) presents a low thermal conductance path between the first
component (1010) and the second component (1004). Heat passing from
one component to another must pass through a lengthy and contorted
path to reach the other component.
[0080] FIG. 10B shows the thermal coupling layer (1006) in its
compressed state. According to one exemplary embodiment, the
adjustable thermal link (1006) is compressed by applying a voltage
across electrodes integral to the piezoelectrically active layer
(1008). The dimensions of the piezoelectrically active layer (1008)
are then altered such that the second component (1004) slides over
the base (1002) and narrows the gap between the first component
(1010) and the second component (1004). As described above, the
adjustable thermal link (1006) is interposed in the gap between the
first component (1010) and the second component (1004). The
adjustable thermal link (1006) is compressed as the spacing between
the two components is reduced. As described in FIG. 8, the thermal
conductance of the adjustable thermal link (1006) increases as more
direct contact between the thermally conductive spacers is
created.
[0081] FIG. 11 illustrates an alternative geometry (1100) in which
an adjustable thermal link (1104) is used to control the
temperature of an optical component (1102). In this illustrative
embodiment, the heat source (1110) is separated from the adjustable
thermal link (1104) by a heat diffuser layer (1108). By way of
example and not limitation the heat source (1110) may be
electronics embedded in an integrated circuit or on a printed
circuit board. The heat diffuser layer (1108) can be used to smooth
the spatial and temporal variations in temperature and heat flux.
By way of example and not limitation, the heat diffuser layer
(1108) may be comprised of a material that is a relatively good
thermal conductor and has a high thermal capacity. The heat
diffuser layer (1108) conducts heat (1111) away from heavily used
electronic components to prevent them from overheating. This heat
is spread over the area that the heat diffuser layer (1108) covers.
Because of its high thermal capacity, the heat diffuser layer
(1108) may also absorb a significant amount of heat with only small
changes in overall temperature. This reduces the temporal
variations in temperature and maintains a more stable operating
environment for the device.
[0082] The heat diffuser layer (1108) is separated from the optical
component (1102) by an adjustable thermal link (1104). The
adjustable thermal link (1104) may take a variety of forms
including, but not limited to the illustrative embodiments shown in
FIGS. 4, 5, 6, 7, and 8.
[0083] A temperature-sensitive component is placed on top of the
adjustable thermal link. In the embodiment illustrated in FIG. 11,
the temperature-sensitive component is an optical component (1102).
The optical component (1102) is cooled by radiation, convection,
and possibly conduction heat transfer to the surroundings. The wavy
arrows (1106) emanating from the upper surface of the optical
component represent the heat loss of the optical component (1102)
to the surroundings. When the heat passed through the adjustable
thermal link (1104) is equal to the heat loss (1106) of the optical
component (1102) the temperature of the optical component will
remain constant. When changing environmental conditions change the
amount of heat loss (1106) or the amount of heat generated (1111),
the thermal conductance of the adjustable thermal link (1104) can
be altered to compensate, thereby keeping the optical component
(1102) at a substantially constant temperature.
[0084] FIG. 12 is a diagram showing one illustrative embodiment-of
an alternative actuation method for adjusting the thermal
conductance of an adjustable thermal link (1205). According to this
exemplary embodiment, a heat source/sink (1215) forms a base upon
which an optical component (1210) and adjustable thermal link
(1205) are placed. The adjustable thermal link (1205) is sandwiched
between the optical component (1210) and the heat source/sink
(1215). The adjustable thermal link (1205) forms the primary heat
path between the optical component (1210) and the heat source/sink
(1215).
[0085] In this exemplary embodiment, the thermal conductance of the
adjustable thermal link (1205) can be altered by adjusting its
vertical thickness. Compressive or expansive pressure is exerted on
the adjustable thermal link (1205) by applying a voltage (1220)
across the adjustable thermal link (1205). This forces charges
(1225, 1230) to the surfaces adjoining the adjustable thermal link
(1205). In the illustrative embodiment shown in FIG. 12, the upper
surface contains positive charges (1225) and the lower surface
contains negative charges (1230). The positive charges (1225) and
negative charges (1230) are mutually attracted to one another and
exert a force that tends to pull the two surfaces together. The
adjustable thermal link (1205) is sandwiched between the two
surfaces and is compressed by the applied voltage.
[0086] In an alternative embodiment, the adjustable thermal link
(1205) may have capacitive plates that form its upper and lower
surfaces. These capacitive plates could be charged as a means of
actuating the adjustable thermal link. The adjustable thermal link
(1205) may take a variety of forms, including but not limited to
the embodiments illustrated in FIGS. 4, 5, 6, 7, and 8.
[0087] FIGS. 13A and 13B show an illustrative micro-electro
mechanical system (MEMS) for controlling the temperature of an
optical component (1302). In the illustrative embodiment shown in
FIG. 13A, MEMS arms (1304, 1310) extend to support a
temperature-sensitive component (1302). The temperature-sensitive
component (1302) is suspended over the surface of a heat
source/sink (1306). An air gap (1308) separates the lower surface
of the temperature-sensitive component (1302) from the upper
surface of the heat source/sink (1306).
[0088] In FIG. 13B, the MEMS arms (1304, 1310) have been deflected
to bring the lower surface of the temperature-sensitive component
(1302) into contact with the heat source/sink (1306). By cycling
between the first position shown in FIG. 13A and the second
position shown in FIG. 13B and adjusting the fraction of time the
temperature-sensitive component (1302) is in each position, the
temperature of the component (1302) can be regulated. In
alternative embodiments, the height of the air gap (1308) could be
adjusted to increase or decrease the convective and radiative heat
transfer between the temperature-sensitive component (1302) and the
heat source/sink (1306). The small air gaps (1308) increase the
heat transfer between the two bodies (1302, 1306), while greater
air gaps (1308) decrease the heat transfer between the two bodies
(1302, 1306).
[0089] In an alternative embodiment, an adjustable thermal link is
interposed between the bottom surface of the temperature-sensitive
component (1302) and the upper surface of the heat source/sink
(1306). The MEMs arms (1304, 1310) then provide the compressive or
tensile force to adjust the thermal conductance of the adjustable
thermal link.
[0090] It will be appreciated by those of skill in the art that an
adjustable thermal link can form a controllable thermal conduit
that can act as a throttle for thermal transfer between various
components in a variety of geometric configurations. By way of
example and not limitation, the adjustable thermal link can be
placed on the upper surface, sides, or underneath a
thermally-sensitive component. Additionally, one or more adjustable
thermal links may be used to control the temperature of a single
component. By way of example and not limitation, a first adjustable
thermal link may connect a temperature-sensitive component to a
heat source and a second adjustable thermal link may connect the
temperature-sensitive component to a separate heat sink.
Additionally, the temperature-sensitive component may be connected
to a heat source by a fixed thermal link and connected to a heat
sink by an adjustable thermal link. Conversely, the
temperature-sensitive component may be connected to a heat source
by an adjustable thermal link and connected to a heat sink by a
fixed thermal link.
[0091] The application of an adjustable thermal link for
temperature control is not limited to component level tasks. For
example an adjustable thermal link may provide thermal control for
a plurality of components, a subsystem, or a complete system.
[0092] FIG. 14 is a flowchart showing one illustrative method of
utilizing an adjustable thermal link to control the temperature of
a component. In a first step, the temperatures of the components
connected by the adjustable thermal link are determined (step
1400). This determination may be made in a variety of ways
including direct temperature measurement, measurement of a
temperature-sensitive component's performance, or other indirect
means. For example, the temperature of a ring resonator may be
estimated by comparing the magnitude of an optical signal contained
within the ring resonator to the available magnitude of a same
optical frequency within the tangential waveguide.
[0093] Next, the desired change in temperature of a target
component is quantified (step 1410). In some circumstances, the
change may be large, such as when the temperature of a ring
resonator is used to shift the ring resonator frequency from one
carrier band to another. Conversely, if it is desirable to correct
the drift of a ring resonator frequency away from the centerline
frequency of a given carrier band, the desired shift may be
relatively small.
[0094] The voltage or current which is to be applied to the
actuating mechanism is then calculated (step 1420). This
calculation may involve accounting for individual differences
between various components, including the application of various
calibration equations or constants. For example, when the target
component is a ring resonator, the applied voltage may vary
depending on the desired shift in the optical resonant frequency,
the geometry of the actuating mechanism, uniformity of the
electrical field produced, and other factors.
[0095] The calculated voltage or current is then applied to the
actuating mechanism which alters the thermal conductance of the
adjustable thermal link (step 1430). Following the application of
the calculated voltage or current, the temperatures of the
components are again measured to see if the thermal transfer
attained by the application of the voltage or current to the
actuator (step 1440) resulted in the desired temperature change or
stabilization. Further adjustments can be made as needed by
repeating steps 1400 through 1440 (step 1450).
[0096] In sum, an adjustable thermal link that couples a heat
source/sink to a second component can be created in a variety of
ways including varying the contact area between two elements,
varying the fraction of time (duty cycle) that the adjustable
thermal link is in a high thermal conduction state, varying the
orientation of anisotropic particles within the thermal coupling
layer, and varying the thermal conduction of the thermal coupling
layer by moving dopant atoms into and out of the thermal coupling
layer.
[0097] Various actuation means can be used to manipulate the
adjustable thermal link's thermal conductance. For example, a
voltage can be applied across a piezo electric actuator to extend
or compress the adjustable thermal link. Electrostatic forces can
be exerted by applying a voltage across two plates to extend or
compress the adjustable thermal link. MEMS devices can be used in a
variety of configurations to provide motion which alters the
thermal conductance of the adjustable thermal link. Additionally,
electrical or magnetic fields align particles within the adjustable
thermal link without deforming the adjustable thermal link.
[0098] The preceding description has been presented only to
illustrate and describe embodiments and examples of the principles
described. This description is not intended to be exhaustive or to
limit these principles to any precise form disclosed. Many
modifications and variations are possible in light of the above
teaching.
* * * * *