U.S. patent application number 14/383297 was filed with the patent office on 2015-03-12 for device and method for forming a temperature gradient.
The applicant listed for this patent is Gerald BOHM, Rudolf HIRSCHMANNER, Siegfried MAIERHOFER. Invention is credited to Gerald Boehm, Rudolf Hirschmanner, Siegfried Maierhofer.
Application Number | 20150068218 14/383297 |
Document ID | / |
Family ID | 48039955 |
Filed Date | 2015-03-12 |
United States Patent
Application |
20150068218 |
Kind Code |
A1 |
Hirschmanner; Rudolf ; et
al. |
March 12, 2015 |
DEVICE AND METHOD FOR FORMING A TEMPERATURE GRADIENT
Abstract
The invention relates to a device (1) for forming a temperature
gradient, having at least one gas-tight working chamber (9) having
a cathode (8) and an anode (7), wherein an inhomogeneous electric
field can be generated when an electric voltage is applied between
the cathode (8) and anode (7) in the working chamber (9), as well
as a working gas between the cathode (8) and anode (7). According
to the invention, a distance between the cathode (8) and anode (7)
is less than 5000 nm in order to enable a heat transport from the
anode (7) to the cathode (8) with the working gas. The invention
further relates to a method for producing a device (1) to form a
temperature gradient. The invention also relates to a method for
forming a temperature gradient between a cathode (8) and an anode
(7) in a working chamber (9) by means of a working gas in the
working chamber (9), to which an inhomogeneous electric field is
applied.
Inventors: |
Hirschmanner; Rudolf;
(Feldbach, AT) ; Maierhofer; Siegfried; (St.
Marein im Muerztal, AT) ; Boehm; Gerald; (Waidhofen
an der Thaya, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HIRSCHMANNER; Rudolf
MAIERHOFER; Siegfried
BOHM; Gerald |
Feldbach |
|
AT
US
US |
|
|
Family ID: |
48039955 |
Appl. No.: |
14/383297 |
Filed: |
March 4, 2013 |
PCT Filed: |
March 4, 2013 |
PCT NO: |
PCT/AT2013/050055 |
371 Date: |
November 18, 2014 |
Current U.S.
Class: |
62/3.1 ;
29/825 |
Current CPC
Class: |
F25B 21/00 20130101;
Y10T 29/49117 20150115; Y02B 30/66 20130101; F25B 2321/001
20130101; Y02B 30/00 20130101 |
Class at
Publication: |
62/3.1 ;
29/825 |
International
Class: |
F25B 21/00 20060101
F25B021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2012 |
AT |
A 50065/2012 |
Claims
1. Device for forming a temperature gradient, comprising at least
one gastight working space (9) having a cathode (8) and an anode
(7), wherein an inhomogeneous electric field can be produced when
an electric voltage is applied between the cathode (8) and the
anode (7) in the working space (9), as well as a working gas
located between the cathode (8) and the anode (7), characterized in
that a distance between the cathode (8) and the anode (7) is less
than 5000 nm in order to enable a heat transport from the anode (7)
to the cathode (8) with the working gas.
2. Device according to claim 1, characterized in that a distance
between the cathode (8) and the anode (7) is less than five times,
preferably less than double, a free path length of the molecules or
atoms of the working gas.
3. Device according to claim 1 characterized in that a distance
between the cathode (8) and the anode (7) is less than a free path
length of the molecules or atoms of the working gas.
4. Device according to claim 1, characterized in that the distance
between the cathode (8) and the anode (7) is less than 2000 nm,
preferably less than 1000 nm, in particular approximately 500
nm.
5. Device according to claim 1, characterized in that the working
space (9) is delimited by a cover plate (3) and a base plate (2)
which are at least partially composed of a dielectric (4).
6. Device according to claim 5, characterized in that the
dielectric (4) comprises a polymer, in particular a Parylene,
and/or a photoresist.
7. Device according to claim 5, characterized in that the base
plate (2) and the cover plate (3) respectively comprise a
substrate, preferably a silicon substrate, which is connected to
the dielectric (4) via an electrically conductive planar electrode
(6).
8. Device according to claim 1, characterized in that the cathode
(8) is formed as a wire electrode (15) which is in particular
composed of gold.
9. Device according to claim 1, characterized in that the at least
one working space (9) has a roughly semicircular cross section.
10. Device according to claim 1, characterized in that the at least
one working space (9) is embodied in a hemispherical shape or in a
roughly pyramidal shape.
11. Device according to claim 1, characterized in that a cross
section of the cathode (8) is less than 3%, preferably less than
1%, in particular less than 0.5%, of a cross section of the working
space (9).
12. Device according to claim 1, characterized in that multiple
working spaces (9) are arranged next to one another, wherein the
individual working spaces (9) are spatially connected to one
another by bridges (13).
13. Device according to claim 12, characterized in that the working
spaces (9) arranged next to one another comprise a shared anode
(7).
14. Device according to claim 12, characterized in that the
cathodes (8) of the working spaces (9) arranged next to one another
are electrically connected to one another.
15. Device according to claim 1, characterized in that multiple
working spaces (9) are arranged serially on top of one another in
multiple layers, wherein heat is transferable between the
layers.
16. Device according to claim 15, characterized in that the
cathodes (8) of the individual layers and the anodes (7) of the
individual layers are respectively electrically connected to one
another.
17. Method for producing a device (1) for forming a temperature
gradient, wherein the device (1) is formed with at least one
gastight working space (9) having a cover plate (3) with a cathode
(8) and a base plate (2) with an anode (7) and a working gas
located therebetween so that an inhomogeneous electric field can be
produced when an electric voltage is applied between the anode (7)
and the cathode (8) in the working space (9), characterized in that
the cover plate (3) is arranged with a distance of less than 5000
nm to the base plate (2).
18. Method according to claim 17, characterized in that the cover
plate (3) is produced using a stamping die (14) produced in a
galvanizing process.
19. Method according to claim 18, characterized in that the
stamping die (14) that is used comprises a galvanic structure (18)
with a roughly semicircular cross section, wherein a radius of the
roughly semicircular cross section is less than 5000 nm, preferably
less than 1000 nm, in particular preferably between 100 nm and 800
nm, particularly approximately 350 nm.
20. Method according to claim 18, characterized in that the
stamping die (14) that is used comprises a metallization layer (19)
with a metallization layer thickness (20) of less than 1000 nm,
preferably less than 500 nm, in particular preferably between 50 nm
and 300 nm, in particular approximately 100 nm.
21. Method according to claim 17, characterized in that an
electrically conductive planar electrode (6) is applied to a
substrate to form the base plate (2) and the cover plate (3).
22. Method according to claim 21, characterized in that a
dielectric (4) is applied to the planar electrode (6).
23. Method according to claim 17, characterized in that roughly
flat planar electrodes (6) are applied to an essentially
plate-shaped substrate layer (5) on two sides, which electrodes
form electrodes of working spaces (9) positioned on top of one
another.
24. Method according to claim 17, characterized in that the cathode
(8) is formed by a wire electrode (15) produced in a lift-off
process.
25. Method for forming a temperature gradient between a cathode (8)
and an anode (7) in a working space (9) by means of a working gas
located in the working space (9), to which gas an inhomogeneous
electric field is applied, characterized in that molecules or atoms
of the working gas carry out a molecular motion and thereby
oscillate between the cathode (8) and the anode (7), wherein these
molecules absorb energy at the anode (7) and release energy at the
cathode (8).
26. Method according to claim 25, characterized in that molecules
or atoms of the working gas essentially only interact with the
anode (7) and the cathode (8) of the working space (9).
27. Method according to claim 25, characterized in that a working
space (9) is used which comprises a distance between the anode (7)
and the cathode (8) which is less than five times, preferably less
than double, a free path length of the molecules or atoms of the
working gas.
28. Method according to claim 25, characterized in that a working
space (9) is used which comprises a distance between the anode (7)
and the cathode (8) which is less than the free path length of the
molecules or atoms of the working gas.
29. Method according to claim 25, characterized in that molecules
or atoms of the working gas are accelerated from the anode (7) in
the direction of the cathode (8) by the electric field.
30. Method according to claim 25, characterized in that molecules
or atoms of the working gas are decelerated at the cathode (8),
wherein energy is released by the molecules or atoms to the cathode
(8).
31. Method according to claim 25, characterized in that a working
gas is used which does not comprise a dipole moment.
32. Method according to claim 25, characterized in that
corresponding processes take place in multiple working spaces (9)
positioned on top of one another, wherein a temperature difference
between a bottommost and a topmost working space (9) is formed
which is greater than the temperature difference that can be
produced with a single working space (9).
Description
[0001] The invention relates to a device for forming a temperature
gradient, comprising at least one gastight working space having a
cathode and an anode, wherein an inhomogeneous electric field can
be produced when an electric voltage is applied between the cathode
and the anode in the working space, as well as a working gas
located between the cathode and the anode.
[0002] Furthermore, the invention relates to a method for producing
a device for forming a temperature gradient, wherein the device is
formed with at least one gastight working space having a cover
plate with a cathode and a base plate having an anode and having a
working gas located therebetween so that an inhomogeneous electric
field can be produced when an electric voltage is applied between
the anode and the cathode in the working space.
[0003] In addition, the invention relates to a method for forming a
temperature gradient between a cathode and an anode in a working
space by means of a working gas located in the working space, to
which working gas an inhomogeneous electric field is applied.
[0004] A device for forming a temperature gradient which is based
on the application of an inhomogeneous electric field is known from
DE 10 2008 021 086 A1 as an electrostatic heat pump. A method with
which a temperature gradient is formed by means of an inhomogeneous
electric field is also theoretically known from the same document.
However, it has been shown that, when the teaching from the
aforementioned document is applied, a temperature gradient cannot
be formed as theoretically predicted and also that no heat can be
transferred according to the teaching.
[0005] It is therefore the object of the invention to disclose a
device of the type named at the outset with which a temperature
gradient can be achieved and heat can be transferred.
[0006] Furthermore, it is an object of the invention to disclose a
method for producing a device of the type named at the outset with
which a device can be produced with which a temperature gradient
can be formed in an electrostatic manner.
[0007] A further object is to disclose a method for forming a
temperature gradient of the type named at the outset, which method
produces a temperature gradient between the anode and the
cathode.
[0008] The first object is attained according to the invention in
that, for a device of the type named at the outset, a distance
between the cathode and the anode is less than 5000 nm to enable a
heat transport from the anode to the cathode with the working
gas.
[0009] Since a force acts on the molecules or atoms (molecules and
atoms are hereinafter used synonymously, since atoms can also be
used in place of molecules and vice versa) of the working gas in
the inhomogeneous electric field, which force effects an
acceleration of the molecules in the direction of the cathode, a
kinetic (thermal) energy of the molecules increases with increasing
displacement in the direction of the cathode. During an impact with
the cathode, the molecules release a part of their kinetic energy
to the cathode, which is thus heated. The molecules are
subsequently reflected by the cathode and move away from the
cathode in an opposing direction, in the direction of the anode.
During a movement of the molecules from the cathode in the
direction of the anode, the molecules are slowed down by the
electric field and lose kinetic energy. An energy difference of the
molecules between the cathode and the anode is equal to that energy
which is necessary to displace the molecules against the electric
field by the distance between the anode and the cathode. The
molecules thus cool down before they impact the anode, for which
reason thermal energy is released to the molecules from the anode
during a contact of the molecules with the anode. At the same time,
the anode is cooled in this manner. The molecules are subsequently
reflected from the anode in the direction of the cathode, wherein
they once again absorb energy on the path to the cathode via the
electric field. The inventors have recognized that a temperature
gradient can only be formed when molecules of the working gas
oscillate between the anode and the cathode in an inhomogeneous
electric field as a result of a molecular motion. Therefore, a
distance between the anode and the cathode must be small enough so
that the molecules oscillate between the anode and the cathode
because of the molecular motion and so that they only interact with
few other molecules between the anode and the cathode, wherein
energy could be released to other molecules or could be absorbed by
these molecules. That means that the molecules of the working gas
essentially only interact with the anode and the cathode.
Preferably, a gas pressure in the working space is smaller than an
ambient pressure in order to be able to reduce an interaction
between gas molecules. In this regard, a gas pressure of less than
500 mbar, preferably between 40 mbar and 100 mbar, in particular
approximately 60 mbar, has proven to be advantageous. Preferably, a
positive electric voltage is applied between the cathode and the
anode. However, proper functioning is also ensured if a polarity of
the applied voltage is reversed, since the molecules or atoms are
always accelerated in the direction of the higher field strength.
The terms anode and cathode used to describe the invention
therefore do not anticipate the polarity of the applied voltage. A
strength of the electric voltage, that is, a potential difference
between the cathode and the anode, results from the dimensions of
the working space used as well as from the desired field strengths.
Anode and cathode refer to those surfaces or regions of the working
space at which electrons or an electric field enter or exit the
working space from a solid body, for example a metal or a
dielectric.
[0010] It is advantageous that a distance between the cathode and
the anode is less than five times, preferably less than double, a
free path length of the molecules or atoms of the working gas. The
interaction between molecules can thus be further reduced.
[0011] Preferably, a distance between the cathode and the anode is
less than a free path length of the molecules or atoms of the
working gas. This makes it possible for the movement of the
molecules between the cathode and the anode to be achieved purely
as a result of the molecular motion of the molecules and for
molecules to oscillate independently in order to transfer energy. A
Knudsen number of the working space, which number indicates a ratio
of the free path length of the working gas to the distance between
the anode and the cathode, is then approximately one or greater
than one.
[0012] Expediently, the distance between the cathode and the anode
is smaller than 2000 nm, preferably smaller than 1000 nm, in
particular approximately 500 nm. An effect for forming a
temperature gradient can thus, as described above, also be achieved
in the case of gas pressures that are achievable with a low design
cost of the working space. For this purpose, a distance between 200
nm and 800 nm in particular has proven to be especially
advantageous.
[0013] Advantageously, the working space is delimited by a cover
plate and a base plate which are at least partially composed of a
dielectric. Since high electric field strengths are applied to the
working space, typically between 10.sup.7 V/m and 10.sup.9 V/m, in
particular approximately 10.sup.8 V/m, at the anode and between
10.sup.8 V/m and 10.sup.10 V/m, in particular approximately
10.sup.9 V/m, at the cathode, dielectrics have proven especially
successful.
[0014] To facilitate a production, it is advantageous that the
dielectric comprises a polymer, in particular a Parylene and/or a
photoresist. These materials have proven to be especially
advantageous for satisfying the requirements in both electrical
terms and also in mechanical terms. Especially the SU-8, a negative
resist used in microsystems engineering, has proven to be
advantageous for forming structures of the indicated
dimensions.
[0015] For the embodiment of the electric field, it is advantageous
that the cover plate is coated at least partially with an
electrically conductive material, preferably a metal, in particular
gold, at a contact surface to the working space. This has also
proven to be advantageous in respect of a heat transfer from the
working space to the cover plate.
[0016] However, it can also be provided that the cover plate is not
gold-plated, in order to save cost in the production. In this case,
electric voltage is transferred to the anode via an essentially
planar metal electrode which is worked into the cover plate. In an
embodiment of this type, the anode is designed as a dielectric
which connects the metal electrode with the working space. This
especially has advantages in respect of production imprecisions
that could lead to a direct contact between the anode and the
cathode. If the anode is designed as a dielectric, a direct contact
between the anode and the cathode does not result in any
impermissibly large current flows. Furthermore, an undesired
distortion of the electric field is avoided.
[0017] Advantageously, the base plate and the cover plate
respectively comprise a substrate, preferably a silicon substrate,
which is connected to the dielectric via an electrically conductive
planar electrode. This material is particularly well-suited to
conducting a heat transferred via the temperature gradient, so that
the device can in particular be used as an electrostatic heat
pump.
[0018] It has proven successful that the cathode is formed as a
wire electrode which in particular is formed from gold. By means of
a cathode that is formed as a wire electrode and an anode embodied
in a planar manner, an inhomogeneous electric field can be formed
in a particularly simple manner, which field is necessary for the
effect described above.
[0019] Preferably, the at least one working space has a roughly
semicircular cross section. An inhomogeneous field can thus be
formed between an anode having a roughly semicircular cross section
and a cathode that is preferably arranged equidistant to the anode
as a wire electrode. Because of the equal distance of the anode to
the cathode, an electric field of this type is particularly
well-suited to forming a temperature gradient according to the
method described above and to transferring heat.
[0020] It is advantageous if the at least one working space is
embodied in a hemispherical shape or in a roughly pyramidal shape.
Calculations and trials have shown that this geometry enables an
improved method because of paths on which the molecules or atoms
move. Advantageously, the wire electrode which forms the cathode
then leads, on a planar boundary area of the hemispherical working
space or the roughly pyramidal working space, roughly diagonally
across this boundary area of the working space. Of course, other
geometric forms of the working space are also possible, such as for
example truncated cones or truncated pyramids.
[0021] For a particularly beneficial design of the electric field,
it is advantageous that a cross section of the cathode is less than
3%, preferably less than 1%, in particular less than 0.5%, of a
cross section of the working space. This enables, in the case of a
planar embodiment of the anode and a positioning of the cathode,
which is preferably embodied as a wire electrode, equidistant to
the anode, an inhomogeneous field which completely fills the
working space. The working space is thus utilized particularly
efficiently.
[0022] For a practical application of the device in which a heat
flow of several watts is transferred, it has proven successful that
multiple working spaces are arranged next to one another, wherein
the individual working spaces are spatially connected to one
another by bridges. Since only a small amount of energy can be
transferred due to the dimensions of each working space,
advantageously multiple working spaces are arranged next to one
another to also be able to transfer larger amounts of energy. The
bridges, which are hollow spaces filled with working gas, also
prevent a temperature difference between the anode and the cathode
from leading to a heat flow from the cathode to the anode via the
base plate and the cover plate. If the working spaces are embodied
in a hemispherical shape or in a roughly pyramidal shape, it is
advantageous to arrange the working spaces next to one another on
two planes so that these planes are arranged in multiple rows and
columns in the form of a grid. Particularly in the case of
pyramidal working spaces, there thus results a high utilization of
the available space on a plane.
[0023] Expediently, the working spaces arranged next to one another
comprise a shared anode. Potential differences between working
spaces positioned next to one another which could lead to undesired
current flows can thus be avoided. Even if the anodes of the
individual working spaces are formed separately, it is advantageous
if the anodes of the individual working spaces are electrically
connected to one another.
[0024] Preferably, the cathodes of the working spaces arranged next
to one another are electrically connected to one another. On the
one hand, this is advantageous in respect of a production; on the
other hand, an electric field with a gradient between the cathodes
is thus avoided, so that the temperature gradient is only generated
between the anode and the cathode. Provided that working spaces
embodied in a hemispheric shape or in a roughly pyramidal shape are
used, this can be achieved particularly easily in that the cathodes
are embodied as wire electrodes which are arranged roughly
diagonally on a planar area through the individual working spaces.
Thus, one wire electrode forms the cathode of multiple working
spaces in a particularly simple manner.
[0025] To achieve large temperature differences, it is advantageous
that multiple working spaces are arranged serially above one
another in multiple layers, wherein heat can be transferred between
the layers. As a result, temperature differences of the individual
layers are added and a total temperature difference of the entire
device can be configured via the number of layers. Since, with one
layer, only a small temperature difference is achievable as a
function of a selected field strength, a working gas used, and the
dimensions of the working space, multiple layers must be placed on
top of one another such that the temperature differences are added.
To transfer heat between the individual layers, the layers are
preferably connected via a thermally conductive material, in
particular a silicon substrate.
[0026] With multiple layers arranged on top of one another, it is
advantageous that the cathodes of the individual layers and the
anodes of the individual layers are electrically connected to one
another respectively. Exceedingly high direct current voltages in
the device are thus avoided which, for example, could lead to an
arcing.
[0027] The second object is achieved according to the invention in
that, in a method for producing a device of the type named at the
outset, the cover plate is arranged at a distance of less than 5000
nm to the base plate.
[0028] As described above, the effect according to the invention is
only achieved and a temperature gradient is only formed in a method
according to the invention if the molecules or atoms of the working
gas essentially do not transfer heat to other molecules of the
working gas, but rather transport heat from the anode to the
cathode. This is enabled with a small distance of the base plate to
the cover plate, wherein preferably a pressure of the working gas
is small enough so that only little interaction can occur between
individual molecules. In this respect, a pressure that is lower
than an ambient pressure, preferably less than 500 mbar, in
particular preferably between 40 mbar and 100 mbar, particularly 60
mbar, has proven to be advantageous.
[0029] Preferably, the cover plate is produced using a stamping die
produced in a galvanizing process. Since the cover plate preferably
comprises a structuring with dimensions within a nanometer range so
that the inhomogeneous electric field can be formed, a
high-precision production method is necessary to be able to produce
corresponding structures. In this respect, a method has proven to
be useful in which a stamping die comprising a negative mold of the
structures that are to be produced is produced in the galvanizing
process. The cover plate is then stamped using the produced
stamping die so that the structures are formed in the cover plate.
To stamp the cover plate with the stamping die, a hot stamping
method is preferably used in which the cover plate is brought to a
deformation temperature and the stamping die is then pressed into
the cover plate in a power-controlled manner and/or a
path-controlled manner, wherein the cover plate is stamped. The
cover plate is subsequently cooled until it has solidified, and the
stamping die is removed from the cover plate.
[0030] To form an advantageous inhomogeneous electric field, the
stamping die which is used preferably comprises a galvanic
structure with a roughly semicircular cross section, wherein a
radius of the roughly semicircular cross section is less than 5000
nm, preferably less than 1000 nm, in particular preferably between
100 nm and 800 nm, particularly roughly 350 nm. The stamping die
preferably comprises a polymer layer applied to a base plate, in
particular a layer which is composed of Parylene or photoresist. To
form the galvanic structure, at least one wire electrode is
arranged on a surface of the stamping die, preferably on the
polymer layer, in a first step. In a further step metal, preferably
gold, is deposited on the wire electrode in a galvanic process by
application of an electric voltage. In this manner, a galvanic
structure is formed around the at least one wire electrode, which
structure comprises the roughly semicircular cross section starting
from the wire electrode as a central point. The cross section of
the structure, which determines dimensions of the working space via
the stamping of the cover plate, can be influenced via the amount
of metal that is deposited on the wire electrode.
[0031] Advantageously, the stamping die that is used comprises a
metallization layer having a metallization layer thickness of less
than 1000 nm, preferably less than 500 nm, in particular preferably
between 50 nm and 300 nm, particularly approximately 100 nm.
Particularly if multiple working spaces are produced next to one
another, it is advantageous to also provide the galvanic structure
with a full-area metallization layer before the stamping of the
cover plate. Bridges between the individual working spaces are thus
formed during the stamping of the cover plate, which bridges
prevent or at least reduce a heat backflow from the cathode to the
anode. The metallization layer is preferably composed of gold or
potassium.
[0032] To form the base plate and the cover plate, an electrically
conductive planar electrode is preferably applied to a substrate.
This has proven to be particularly advantageous for the electric
field required in the method according to the invention.
[0033] Expediently, a dielectric is applied to the planar
electrode. Because of the high electric field strengths, this is
advantageous for achieving the desired formation of the electric
field.
[0034] To achieve a particularly suitable contacting, a contact
surface between the cover plate and the working space is coated
with a metal, in particular gold. A thusly produced planar
metallization of the contact surface then forms the anode, which is
embodied as a planar electrode. If multiple working spaces are
arranged next to one another, the anodes of the individual working
spaces are connected via the planar metallization. Gold exhibits
favorable properties in respect of electrical conductivity,
chemical resistance and thermal conduction, for which reason gold
is preferably used on the anode.
[0035] However, it can also be provided that the contact surface
between the working space and the cover panel, which forms the
anode, is designed as a dielectric. This has advantages in the
event of a direct contact between the anode and the cathode
occurring due to imprecisions during the production. If the anode
is designed as a dielectric, high currents and field distortions
are avoided in the case of a direct contact. The production can
also be simplified by this measure, in which the face of the anode
is not coated.
[0036] To form a device which comprises multiple working spaces
arranged next to one another and on top of one another to be able
to produce large temperature differences, multiple base plates and
cover plates are stacked on top of one another. It can thereby be
provided that one plate can be embodied on a top side as a base
plate and one plate on a bottom side as a cover plate in order to
design a production process in a simpler manner and to improve a
heat transfer from one layer to a next layer.
[0037] To simplify the production, it is advantageous if roughly
flat planar electrodes are applied to an essentially plate-shaped
substrate layer on two sides, which electrodes form electrodes of
working spaces positioned on top of one another. Those parts via
which an electric voltage is conducted from outside the device into
the region of the working space are thereby referred to as
electrodes. However, these electrodes do not need to lead directly
into the working space, since the electric field is also formed
when the electrodes lead to a region bordering the working space,
for example to a dielectric. Preferably the electric voltage that
generates the electric field is applied to these electrodes in the
method. This simplifies the production and reduces costs in the
production. The substrate layer is thereby advantageously composed
of a dielectric, whereby high currents inside the substrate layer
from an electrode of a layer to the electrode of the layer
positioned thereabove are prevented. A thickness of the substrate
layer which defines a distance between the cathode and the anode is
thereby determined as a function of a desired maximum current
inside the plate and of a conductance of the dielectric selected.
Typically, currents inside the substrate layer are less than
10.sup.-5 A, in particular less than 10.sup.-10 A, preferably
smaller than 10.sup.-15 A. Because the substrate layer in this
embodiment assumes both a structural function concerning a gastight
separation of working spaces positioned on top of one another and
also an electric function concerning the supply of an electric
potential to working spaces positioned on top of one another, the
production can occur in a particularly cost-effective manner.
[0038] It can also be preferred that the cathode is formed by a
wire electrode produced in a lift-off process. The lift-off process
has proven successful for producing structures within the nanometer
range. A sacrificial layer, usually a photoresist, is thereby
deposited on a substrate in a first step. The sacrificial layer is
then structured using an inverse pattern of the eventual structure.
This preferably occurs in a hot-stamping process or by means of
photolithography.
[0039] After the structuring, metal, preferably gold, is deposited
across the entire area on the structured surface, wherein the metal
is deposited on the substrate in the region of the structuring. In
a final step, the sacrificial layer is removed in a wet-chemical
manner, for example using a solvent, wherein the metal that was
deposited on a top side of the sacrificial layer is lifted and
removed. Thus, only the metal in the regions of the structuring
remains, where metal is in direct contact with the substrate. In
this manner, the wire electrodes within the nanometer range can be
produced particularly precisely and cost-effectively.
[0040] The third object is attained in that, in a method for
forming a temperature gradient of the type named at the outset,
molecules or atoms of the working gas carry out a molecular motion
and thereby oscillate between the cathode and the anode, wherein
these molecules or atoms absorb energy at the anode and release
energy at the cathode.
[0041] Because the molecules or atoms oscillate independently
between the anode and the cathode due to the molecular motion,
energy can be inputted into the molecules through the electric
field during a movement in the direction of the cathode, whereby a
kinetic (thermal) energy of the molecules is increased. At the
cathode, the molecules release energy to the cathode, whereby the
cathode is heated. The molecules are then reflected in the
direction of the anode. In a subsequent motion in the direction of
the anode, the kinetic (thermal) energy of the molecules decreases,
since these molecules are moved against the electric field, whereby
the molecules can absorb energy at the anode before they are once
again reflected in the direction of the cathode. Only by means of
an independent oscillation of the molecules as the result of the
molecular motion does the method become effective and lead to the
formation of a temperature gradient between the anode and the
cathode, whereby heat is transferred by means of an electrostatic
process.
[0042] Preferably, molecules or atoms of the working gas
essentially only interact with the anode and the cathode of the
working space. This prevents an undesired heat transfer between
molecules among one another, whereby the effect described above
would appear to a considerably lesser extent, since molecules could
already be cooled before arriving at the cathode. Preferably, the
dimensions of the working space and the thermodynamic states of the
working gas are chosen such that a molecule on the path between the
anode and the cathode only strikes another molecule with a very low
probability. This can be influenced particularly easily by a
distance from the anode to the cathode in the working space and a
pressure of the working gas.
[0043] Advantageously, a working space is used which comprises a
distance between the anode and the cathode which is less than five
times, preferably less than double, a free path length of the
molecules or the atoms of the working gas. With an embodiment of
this type of the working space, the method for forming the
temperature gradient can be achieved particularly advantageously,
since little interaction takes place between molecules.
[0044] Particularly preferably, a working space is used which
comprises a distance between the anode and the cathode which is
less than the free path length of the molecules or the atoms of the
working gas. In this manner, a movement of the molecules between
the anode and the cathode is guaranteed as a result of the
molecular motion. A Knudsen number of the working space, which
indicates a ratio of the free path length of the working gas to the
distance between the anode and the cathode, is then approximately
one or slightly greater than one.
[0045] It has proven successful that the molecules or atoms of the
working gas are accelerated from the anode in the direction of the
cathode by the electric field. Energy is thus inputted into the
molecules, which release this energy to the cathode to transfer
heat and to form the temperature gradient.
[0046] It is advantageous that molecules or atoms of the working
gas are decelerated at the cathode, wherein energy is released from
the molecules or the atoms to the cathode. A temperature gradient
between the anode and the cathode is thereby formed which enables a
heat flow.
[0047] It is advantageous if a working gas is used which does not
comprise a dipole moment. Due to the electric field, a working gas
without a dipole moment is polarized and the molecules of the
working gas are aligned according to the electric field and are
accelerated by the electric field. Because the dipole moment of the
working gas is induced by the electric field, a polarization of the
molecules is retained even after an impact of the molecules with
the anode or the cathode. In contrast to a working gas which
comprises a dipole moment, an alignment of the molecules as in the
case of a working gas with a static dipole moment does not occur.
Preferably, a working gas is used which has a high polarizability
and a high mass in order to maximize a transferable heat flow per
volume. In this regard, particularly gases or molecules that can be
brought into the gas phase, such as argon, xenon, C.sub.60,
C.sub.60F.sub.60, iodine, SF.sub.6, and UF.sub.6 have proven
successful.
[0048] Expediently, corresponding processes take place in multiple
working spaces positioned on top of one another, wherein a
temperature difference between a bottommost working space and a
topmost working space is formed which is larger than the
temperature difference that can be produced with a single working
space. In this manner, a greater temperature difference is formed
than that which would be possible with a single layer, whereby heat
flows of several megawatts can be transferred.
[0049] Additional features, advantages and effects of the invention
follow from the exemplary embodiment illustrated below. The
drawings which are thereby referenced show the following:
[0050] FIG. 1 through FIG. 5 show devices according to the
invention for forming a temperature gradient;
[0051] FIG. 6 shows a stamping die for producing a device according
to FIG. 1 in a first production step;
[0052] FIGS. 7 and 8 show the stamping die according to FIG. 6 in
additional process steps.
[0053] FIG. 1 shows a device 1 according to the invention for
forming a temperature gradient, wherein a base plate 2 and a cover
plate 3 are visible. In the present exemplary embodiment, the base
plate 2 and the cover plate 3 are respectively formed from a
substrate layer 5, preferably composed of a silicon substrate, onto
which respectively one planar electrode 6 is applied. A layer
composed of a dielectric 4 is applied respectively to the planar
electrodes 6. The planar electrodes 6, which are arranged between
the layer of the dielectric 4 and the substrate respectively in the
base plate 2 and cover plate 3, are composed preferably of gold, in
particular to be able to conduct a heat especially well which is
transported in a method according to the invention. As can be seen
in FIG. 1, the base plate 2 comprises an essentially planar surface
on which cathodes 8 formed as wire electrodes are arranged. The
cover plate 3 comprises a structuring on that side which opposes
the base plate 2. The surface of the structured side is covered by
a metallization which is preferably formed from gold and forms
anodes 7. Because of the structuring of the cover plate 3, the
planar embodiment of the anodes 7 and a line-shaped embodiment of
the cathodes 8, an inhomogeneous electric field forms when an
electric voltage is applied between the anodes 7 and the cathodes
8, which field is essential for the formation of a temperature
gradient. In the present exemplary embodiment, the structuring of
the cover plate 3 is embodied in a roughly semicircular shape in
order to allow a uniform distance from the planar anode 7 to the
line-shaped cathode 8. This enables an electric field, which is
particularly advantageous for the formation of a temperature
gradient. The device 1 comprises an extension in a direction
perpendicular to an illustrated drawing plane so that the
structuring in the cover plate 3 essentially comprises
semicylindrical surfaces. A working space 9 which is formed between
respectively a cathode 8 and the semicircular anode 7 across from
the cathode 8 is filled by a working gas. In FIG. 1, three working
spaces 9 are fully depicted in cross section, wherein the
individual working spaces 9 are connected among one another by
bridges 13. The bridges 13 prevent a heat flow from the cathode 8
to the anode 7 via the layer which is formed from a dielectric 4. A
minimum distance 11 between the base plate 2 and the cover plate 3,
which distance exists because of the bridges 13, is approximately
100 nm in the exemplary embodiment illustrated. A polymer, in
particular a Parylene, or a photoresist is used, preferably the
commercially available SU-8, as a dielectric 4. To accurately
position the cover plate 3 and the base plate 2, spacers which are
not depicted are arranged between the base plate 2 and the cover
plate 3, which spacers have the dimensions of the minimum distance
11 between the base plate 2 and the cover plate 3 to ensure the
minimum distance 11. To enable a method for forming a temperature
gradient with the device 1, the dimensions of the working space 9
and the space between the base plate 2 and the cover plate 3 are to
be chosen such that the distance between the cathode 8 and the
anode 7 is roughly equal to a free path length of molecules or
atoms of the working gas. This is dependent upon the working gas
used and a pressure in the working space 9. In the present
exemplary embodiment, the minimum distance between the cathode 8
and the anode 7 is respectively approximately 500 nm; the cathode 8
has a circular cross section with a diameter of approximately 50
nm. The minimum distance 11 between the base plate 2 and the cover
plate 3 in the region of the bridges 13 is approximately 100 nm.
The dielectric 4 of the base plate 2 has a dielectric thickness 12
of approximately 350 nm. The anodes 7 of the individual working
spaces 9 are connected among one another in the region of the
bridges 13 in an electrically conductive manner by the
metallization which covers the entire structured surface of the
cover plate 3. To prevent current flows between the individual
cathodes 8, the individual cathodes 8 are also electrically
connected among one another. Since only small temperature
differences and transferable heat flows are achievable with a
single working space 9 due to the small dimensions, multiple
working spaces 9, as indicated in FIG. 1, are arranged next to one
another. In addition, multiple working spaces 9 are also positioned
on top of one another so that the temperature differences of the
individual layers can be added and so that large heat flows can
also be transferred. To avoid high potential differences between
the individual layers, it has proven successful to electrically
connect all of the anodes 7 among one another and to electrically
connect the cathodes 8 among one another. An inert gas without a
dipole moment is used as a working gas. The working space 9 can be
embodied as schematically illustrated in FIG. 1. Preferably, sharp
edges, in particular in the region of the bridges 13, can also be
rounded to avoid peak discharges. However, it can also be
preferably provided that the anodes 7 of the working spaces 9 are
not coated, so that the anodes 7 are formed from the dielectric 4
and so that no metallization is provided on the anodes 7. This has
proven to be expedient in a direct contact between the anode 7 and
the cathode 8 and therefore for avoiding current flows and field
distortions. In addition, a production is thus also simplified.
Because of the dimensions within the nanometer range, a direct
contact cannot be ruled out in particular due to production
imprecisions.
[0054] FIGS. 2 and 3 show a further device 1 according to the
invention in a side view and top view, which device in contrast to
the device 1 according to FIG. 1, however, does not have any
significant extension in a direction perpendicular to an
illustrated drawing plane, but rather comprises roughly pyramidal
working spaces 9 which are again connected via bridges 13. In
particular, this has the advantage that atoms or molecules cannot
be deflected in the direction of the extension and that an
efficiency is increased. Further, the device 1 according to FIGS. 2
and 3 does not comprise any metallized anodes 7 in order to avoid
an undesired current flow and a field distortion in the event of
production imprecisions which could lead to a contact between the
anode 7 and the cathode 8.
[0055] The anode 7 at which electrons enter or exit the working
space 9 depending on a polarization of the applied voltage is
formed by the dielectric 4 in the device 1, which is illustrated in
FIGS. 2 and 3. The voltage is applied to the planar electrodes 6
which are arranged on the substrate layer 5. In FIG. 3, it can be
recognized in the top view that multiple working spaces 9 are
arranged next to one another in multiple rows and columns in order
to transfer larger current flows. Preferably, multiple layers are
arranged on top of one another, wherein it is advantageous to apply
two planar electrodes 6 to a roughly plate-shaped substrate layer
5, which electrodes are used as voltage supplies for the working
spaces 9 arranged below and above the substrate layer 5. Thus, the
base plate 2, the substrate layer 5 and the cover plate 3 with
worked-in planar electrodes 6 can be pre-produced as a single
element. For an assembly of the device 1, the pre-produced elements
can then only be positioned above one another. The base plate 2 of
a working space 9 positioned above the base plate 2 is then a part
of the same element which forms the cover plate 3 of a working
space 9 positioned therebeneath. A distance of the planar
electrodes 6 that are arranged on a substrate layer 5 is preferably
chosen such that a flow from a planar electrode 6 through the
substrate layer 5 onto the second planar electrode 6 arranged on
the substrate layer 5 is less than 10.sup.-5 A, preferably
10.sup.-10 A, in particular 10.sup.-15 A. Along with the distance,
this flow is dependent upon the conductance of the material of the
substrate layer 5 and upon the selected voltage between the anode 7
and the cathode 8. The device 1 according to FIGS. 2 and 3
essentially has similar main dimensions to the device 1 shown in
FIG. 1, wherein the working space 9 has a maximum height of
approximately 450 nm. An electrode distance 21 of the planar
electrode 6, which is arranged above the anode 7, to the cathode 8
is approximately 800 nm so that a distance between two planar
electrodes 6 of a working space 9 is approximately 1150 nm. A
distance from a wire electrode 15 to a wire electrode preferably
positioned parallel next to it is approximately 1100 nm. Between
the working spaces 9, bridges 13 are once again provided which
ensure a minimum distance 11 of approximately 100 nm.
[0056] FIGS. 4 and 5 show a further device 1 according to the
invention in a side view and top view, which device only differs
from the device 1 depicted in FIGS. 2 and 3 in that the working
space 9 is not embodied as a full pyramid, but rather as a
truncated pyramid. The essential dimensions are embodied
analogously to the devices 1 according to FIGS. 1 through 3. A
maximum height of the working space in the shape of a truncated
pyramid is approximately 550 nm.
[0057] FIG. 6 shows a stamping die 14 which is used to produce the
cover plate 3 from FIG. 1 in a first production step. In a process
step according to FIG. 6, the stamping die 14 is composed of a base
plate 17 which, similar to the base plate 2 according to FIG. 1, is
formed from a substrate and a dielectric 4. A silicon substrate is
preferably used as a substrate; a polymer, in particular Parylene,
or a photoresist, in particular the photoresist SU-8, is preferably
used as a dielectric 4. On the surface of the dielectric 4 of the
stamping die 14, which is essentially embodied in a planar manner,
wire electrodes 15 are arranged which essentially have a circular
cross section. The wire electrodes 15 are preferably formed in a
lift-off process, wherein sharp edges are rounded by tempering. It
has thereby proven to be advantageous to use a lift-off process
based on an electron beam lithography, wherein gold is preferably
used as a wire material. Preferably, Parylene on silicon is used as
a substrate material for the lift-off process. To round the edges
of the wire electrodes 15 produced in the lift-off process, which
electrodes have a width of less than 100 nm and wire spacings of
approximately 1 .mu.m, the wire electrode 15 is tempered following
the lift-off process. In this process step, the surface roughness
and the wire shape are optimized at approximately 50.degree. C. to
500.degree. C., preferably 100.degree. C. to 300.degree. C. The
stamping die 14 preferably has the same extension in a direction
perpendicular to the illustrated sectional plane as the device 1
according to FIG. 1 in order to be able to design the production in
a simple manner. To produce the structure illustrated in FIG. 1 in
the dielectric 4 of the cover plate 3, which structure essentially
comprises semicylindrical recesses in the cover plate 3, the cover
plate 3 is heated until the dielectric 4 has transitioned into a
deformable state. A negative mold of the structuring is then
pressed into the dielectric 4 so that the desired structuring is
formed in the dielectric 4. The negative mold or stamping die 14 is
formed in that, as illustrated in FIG. 7, a galvanic structure 18
is applied to the stamping die 14 according to FIG. 6 in a further
process step, which structure has an essentially semicircular cross
section for each working space 9. For this purpose, metal is
deposited on the wire electrodes 15 in a galvanizing process,
wherein a galvanic structure 18 forms around each wire electrode
15, which structure has a semicircular cross section. To form the
cover plate 3 from FIG. 1, which has a working space radius 10 of
approximately 500 nm, metal is deposited on the wire electrode 15
until the galvanic structure 18 has a structural radius 16 of
approximately 350 nm. If, as illustrated in the exemplary
embodiment, a working space 9 with a roughly circular cross section
is used, the working space radius 10 is equal to the minimum
distance between the anode 7 and the cathode 8. To stamp the
bridges 13 which connect the individual working spaces 9 among one
another and enable a minimum distance 11 between the base plate 2
and the cover plate 3, a metallization layer 19 is applied to the
galvanic structure 18.
[0058] FIG. 8 shows the stamping die 14 from FIG. 7, wherein a
full-area metallization layer 19 with a metallization layer
thickness 20 of approximately 100 nm is applied to the galvanic
structure 18 in a further processing step. The full-area
metallization is preferably composed of gold or potassium. These
metals have proven particularly successful for stamping the desired
structure into the cover plate 3. The devices 1 according to FIGS.
2 through 4 are produced in an analogous manner with adapted
stamping dies 14, wherein the application of a metallization to the
anode 7 as explained above is not mandatory.
[0059] To form a temperature gradient and to transfer heat with the
device 1 from FIG. 1, an electric voltage is applied to the anode 7
and the cathode 8 or to the planar electrodes 6 so that an
inhomogeneous electric field is produced in the working space 9.
The electric field thereby has a field strength of approximately
10.sup.8 V/m at the anode and a field strength of approximately
10.sup.9 V/m at the cathode. As a result of the electric field,
molecules of the working gas which is preferably free of a dipole
moment are polarized and accelerated in the direction of the
cathode 8. Since the minimum distance between the anode 7 and the
cathode 8, the working space radius 10, is roughly equal to a free
path length of the molecules of the working gas, the molecules of
the working gas oscillate constantly between the anode 7 and the
cathode 8. A pressure in the working space is typically smaller
than an ambient pressure, preferably smaller than 500 mbar, in
particular preferably between 40 mbar and 100 mbar, particularly
approximately 60 mbar. Because of an acceleration which the
molecules experience during a movement from the anode 7 to the
cathode 8, a kinetic and therefore thermal energy of the molecules
increases. During the impact of the molecules on the cathode 8, the
molecules release heat to the cathode 8, whereby a heating of the
cathode 8 occurs. The molecules are then reflected by the cathode 8
and move in the direction of the anode 7. During a movement in this
direction, the kinetic and thermal energy of the molecules
decrease, since they are moved against the electric field. The
molecules are thus cooled until they arrive at the anode 7 and
absorb energy from the anode 7 in the form of heat during an impact
with the anode 7. The molecules are then reflected again in the
direction of the cathode 8. Preferably, a working gas without a
dipole moment, in particular an inert gas, is used. However, it is
also possible to use a working gas which has a dipole moment.
Molecules of a working gas of this type are aligned in the
direction of the electric field by the electric field.
[0060] With a method according to the invention, it is possible to
form a temperature gradient by means of an electrostatic field. For
example, a temperature difference of approximately 1.5 K to 3.5 K
can be achieved with a device as illustrated schematically in FIG.
1. It is thus possible to omit mechanically moved parts that are
used in conventional devices to form a temperature gradient,
whereby signs of wear and noises are avoided. Through an
arrangement of multiple layers on top of one another, the
achievable temperature difference can be increased. With a method
according to the invention and a device 1 according to the
invention, large temperature differences can also be produced and
heat flows of several megawatts can be transferred with a
corresponding arrangement of multiple working spaces 9 next to one
another and on top of one another.
* * * * *