U.S. patent application number 09/811688 was filed with the patent office on 2002-09-19 for light emitting diodes with spreading and improving light emitting area.
Invention is credited to Chen, Chien-An, Chen, Nai-Chuan, Wu, Bor-Jen, Yih, Nae-Guann.
Application Number | 20020130327 09/811688 |
Document ID | / |
Family ID | 25207264 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020130327 |
Kind Code |
A1 |
Wu, Bor-Jen ; et
al. |
September 19, 2002 |
LIGHT EMITTING DIODES WITH SPREADING AND IMPROVING LIGHT EMITTING
AREA
Abstract
The present invention provides a light semiconductor device
comprising a substrate and a first semiconductor structure on the
substrate. A light emitting structure is on a first portion of the
first semiconductor structure. A first contact structure is on a
second portion of the first semiconductor structure. The second
portion is separated from the first portion of the first
semiconductor structure. The first contact structure has a first
shape. A second semiconductor structure is on the light emitting
structure. A transparent contact is on the second semiconductor
structure and has a cut-off portion to expose the portion of second
semiconductor structure and a second shape. A second contact
structure is on the cut-off portion of the transparent contact. The
second contact structure contacting the second semiconductor has a
third shape. The second contact structure with the third shape is
corresponded to both the transparent contact with the second shape
and the first contact structure with the first shape whereby a
relationship provides a plurality of current paths with
substantially equal distances between the first contact structure
and the second contact structure.
Inventors: |
Wu, Bor-Jen; (Taipei City,
TW) ; Yih, Nae-Guann; (Tao-Yuan, TW) ; Chen,
Chien-An; (Hsin-Chuang City, TW) ; Chen,
Nai-Chuan; (Pan-Chiao City, TW) |
Correspondence
Address: |
POWELL, GOLDSTEIN, FRAZER & MURPHY LLP
P.O. BOX 97223
WASHINGTON
DC
20090-7223
US
|
Family ID: |
25207264 |
Appl. No.: |
09/811688 |
Filed: |
March 19, 2001 |
Current U.S.
Class: |
257/80 |
Current CPC
Class: |
H01L 33/42 20130101;
H01L 33/20 20130101; H01L 33/385 20130101 |
Class at
Publication: |
257/80 |
International
Class: |
H01L 033/00 |
Claims
What is claimed is:
1. a light semiconductor device comprising: a substrate; a first
semiconductor structure on said substrate; a light emitting
structure on a first portion of said first semiconductor structure;
a first contact structure on a second portion of said first
semiconductor structure, said second portion separated from said
first portion of said first semiconductor structure, said first
contact structure having a first shape; a second semiconductor
structure on said light emitting structure; a transparent contact
on said second semiconductor structure, said transparent having a
cut-off portion to expose said portion of second semiconductor
structure and a second shape; and a second contact structure on
said cut-off portion of said transparent contact, said second
contact structure contacting said second semiconductor and having a
third shape, said second contact structure with said third shape
corresponded to both said transparent contact with said second
shape and said first contact structure with said first shape
whereby a relationship provides a plurality of current paths with
substantially equal distances between said first contact structure
and said second contact structure.
2. The device according to claim 1, wherein said transparent
contact comprises a plurality of hollow patterns which can provide
light emitting directly from said transparent contact and is used
for turning directions of said current paths.
3. The device according to claim 1, wherein said first shape
comprises a first arc-shape edge.
4. The device according to claim 3, wherein said second shape
comprises a second arc-shape edge, and any a point on said second
arc-shape edge has substantially equal distance to said first
arc-shape edge.
5. The device according to claim 3, wherein said third shape
comprises a third arc-shape edge, and any a point on said third
arc-shape edge has substantially equal distance to said first
arc-shape edge.
6. The device according to claim 1, wherein said first shape
comprises a ring shape whereby said transparent contact is enclosed
in by said first shape of said first contact structure.
7. The device according to claim 6, wherein said second contact
structure is at center of said transparent contact, thus provides
said current paths with substantially equal distance from said
second contact structure to ring-shape first contact structure.
8. The device according to claim 1, wherein said third shape
comprises a ring shape whereby said ring-shape second contact
structure is in interior of said transparent contact.
9. The device according to claim 8, wherein said first contact
structure has a position underlay near center of said ring-shape
second contact structure whereby said current paths have
substantially equal distances.
10. The device according to claim 1, wherein said first shape
comprises having a first line shape and said first line-shape first
contact structure is positioned at a first side of said transparent
contact.
11. The device according to claim 10, wherein said third shape
comprises a second line shape and said second line-shape is
positioned at a second side opposite to said first side of said
transparent contact, whereby said current paths have substantially
equal distances.
12. The device according to claim 1, wherein said first contact
structure and said second contact structure have opposite
conductivity.
13. The device according to claim 1, wherein said first
semiconductor structure and said first contact structure have same
conductivity.
14. The device according to claim 1, wherein said second
semiconductor structure and said second contact structure have same
conductivity.
15. The device according to claim 1, wherein material of said
substrate comprises sapphire.
16. The device according to claim 1, wherein material of said
substrate comprises a conductive material under a normal operated
condition of conduction blocking in the vertical direction.
17. The device according to claim 1, wherein said first and second
semiconductor structures comprise having compositions of
Al.sub.XGa.sub.YIn.sub.(1-X-Y)N-based epitaxyl layer where both X
and Y have values between 0 and 1, individually.
18. The device according to claim 1, wherein said first and second
semiconductor structures comprise an individual single layer
structure.
19. The device according to claim 1, wherein said first and second
semiconductor structure comprises a multi-layer structure.
20. The device according to claim 1, wherein said transparent
contact comprises a nickel oxide/gold layer.
21. The device according to claim 1, wherein said first and second
contact structures comprise an individual contact layer and an
individual electrode.
22. The device according to claim 1, wherein said light emitting
structure is selected from groups consisting of homogenous
junction, double hetero-junction, single quantum well structure,
and multi quantum well structure.
23. The device according to claim 1 further comprising a
passivation layer covering on said transparent contact and at a
plurality of side walls of said first contact structure and said
second contact structure.
24. The device according to claim 23, wherein said passivation
layer is selected form groups consisting of aluminum oxide, silicon
oxide, silicon nitride, tantalum oxide, titanium oxide, calcium
fluoride, hafnium oxide, zinc sulfide and zinc oxide.
25. a light emitting diode device comprising: a substrate; a first
semiconductor structure on said substrate, said first semiconductor
structure having a first conductivity; a light emitting structure
on a first portion of said first semiconductor structure; a first
contact structure with said first conductivity on a second portion
of said first semiconductor structure, said second portion
separated from said first portion of said first semiconductor
structure, said first contact structure having a first shape; a
second semiconductor structure on said light emitting structure,
said second semiconductor having a second conductivity opposite to
said first conductivity; a transparent contact on said second
semiconductor structure, said transparent having a cut-off portion
to expose said portion of second semiconductor structure and a
second shape; and a second contact structure with said second
conductivity on said cut-off portion of said transparent contact,
said second contact structure contacting said second semiconductor
and having a third shape, said second contact structure with said
third shape corresponded to both said transparent contact with said
second shape and said first contact structure with said first shape
whereby a relationship provides a plurality of current paths with
substantially equal distances between said first contact structure
and said second contact structure.
26. The device according to claim 25, wherein said transparent
contact comprises a plurality of hollow patterns which can provide
light emitting directly from said transparent contact and is used
for turning directions of said current paths.
27. The device according to claim 25, wherein said first shape
comprises a first arc-shape edge.
28. The device according to claim 27, wherein said second shape
comprises a second arc-shape edge, and any a point on said second
arc-shape edge has a substantially equal distance to said first
arc-shape edge.
29. The device according to claim 27, wherein said third shape
comprises a third arc-shape edge, and any a point on said third
arc-shape edge has a substantially equal distance to said first
arc-shaped edge.
30. The device according to claim 25, wherein said first shape
comprises a ring shape whereby said transparent contact is enclosed
in by said first shape of said first contact structure.
31. The device according to claim 25, wherein said second contact
structure is at center of said transparent contact, thus provides
said current paths with substantially equal distance from said
second contact structure to ring-shape first contact structure.
32. The device according to claim 25, wherein said third shape
comprises a ring shape whereby said ring-shape second contact
structure is in interior of said transparent contact.
33. The device according to claim 32, wherein said first contact
structure has a position underlay near center of said ring-shape
second contact structure whereby said current paths have
substantially equal distances.
34. The device according to claim 25, wherein said first shape
comprises having a first line shape and said first line-shape first
contact structure is positioned at a first side of said transparent
contact.
35. The device according to claim 34, wherein said third shape
comprises a second line shape and said second line-shape is
positioned at a second side opposite to said first side of said
transparent contact, whereby said current paths have substantially
equal distances.
36. The device according to claim 25, wherein material of said
substrate comprises sapphire.
37. The device according to claim 25, wherein material of said
substrate comprises a conductive material under a normal operated
condition of conduction blocking in the vertical direction.
38. The device according to claim 25, wherein said first and second
semiconductor structures comprise having compositions of
Al.sub.XGa.sub.YIn.sub.(1-X-Y)N-based epitaxyl layer where both X
and Y have values between 0 and 1, individually.
39. The device according to claim 25, wherein said first and second
semiconductor structures comprise an individual single layer
structure.
40. The device according to claim 25, wherein said first and second
semiconductor structure comprises a multi-layer structure.
41. The device according to claim 25, wherein said transparent
contact comprises a nickel oxide/gold layer.
42. The device according to claim 25, wherein said first and second
contact structures comprise an individual contact layer and an
individual electrode.
43. The device according to claim 25, wherein said light emitting
structure is selected from groups consisting of homogenous
junction, double hetero-junction, single quantum well structure,
and multi quantum well structure.
44. The device according to claim 25 further comprising a
passivation layer covering on said transparent contact and at a
plurality of side walls of said first contact structure and said
second contact structure.
45. The device according to claim 44, wherein said passivation
layer is selected form groups consisting of aluminum oxide, silicon
oxide, silicon nitride, tantalum oxide, titanium oxide, calcium
fluoride, hafnium oxide, zinc sulfide and zinc oxide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to light emitting diodes, and more
particularly to light emitting diodes with spreading current and
improving light emitting area.
[0003] 2. Description of the Prior Art
[0004] For photonic semiconductor device, light emitting diode
(LED) may be the most commonly recognized because of its
application to such a wide variety of products and applications
such as scientific equipment, medical equipment and, perhaps most
commonly, various consumer products in which LEDs form the light
source for various signals, indicators, gauges, clocks, and many
other familiar items. Semiconductor sources such as LEDs are
particularly desirable as light output devices in such items
because of their generally long lifetime, low power requirement,
and their high reliability.
[0005] Since early 1970s, gallium nitride (GaN)-based material has
attracted attentions in applications to light emitters because of
its wide bandgap nature. On the other hand, insulating and lattice
mismatched substrate, such as sapphire (aluminum oxide,
Al.sub.2O.sub.3) with its thermal stability, and optical
transparency, has been widely used for the application to Group III
nitrides because there is not any substrate of matched lattice. In
U.S. Pat. No. 4,153,905, the planner GaN-based LED structure grown
on the sapphire substrate with both n-type and p-type layers with
corresponding ohmic contacts is proposed. However, it is still
difficult to prepare a highly conductive p-type GaN layer.
Therefore, it is more difficult to make p-type ohmic contacts on
and spread current in the p-type GaN layer.
[0006] Recently, both Akasaki et al. And Nakamura et al. have
implemented the methods to improve conductivity of p-type GaN
layers. However, the conductivity of the p-type GaN is still
inferior to that of n-type one. Consequently, the p-type GaN layer
is the topmost layer of the GaN-based LED structure, while a
transparent contact on the p-type layer becomes indispensable for
the better performance of a device. For the most utility of the
light emitting surface, the n-type and p-type contacts have been
placed as wide apart as possible, i.e. at the opposite corners of a
device.
[0007] FIG. 1 is a plan view of a semiconductor light-emitting
device having a GaN-based substrate according to a prior art. A
cut-off portion 117 is provided in a p-type transparent electrode
115, exposing a portion of the surface of a p-type semiconductor
layer 113. A bonding pad 116 strongly adheres to the p-type
semiconductor layer 113 through the cut-off portion 117, and is
electrically connected with the p-type transparent electrode 115.
The cut-off portion 117, and hence the bonding pad 116, are
arranged farthest from the n-electrode 114 provided on an n-type
semiconductor layer 112. But the arrangement for the contacts has
the disadvantage of current crowding happening between these
electrodes. As a result, the light emitting surface is not utilize
efficiently, and the lifetimes of the transparent contact and the
device are shorten by the current crowding.
SUMMARY OF THE INVENTION
[0008] One of the objectives of the present invention is to provide
light emitting diodes with spreading current and improving light
emitting area. Multitude of hollow patterns opened on the
transparent contact can block the current shortcuts and further
spread current and enhance the light emitting area.
[0009] Another one of the objectives of the present invention is to
provide light emitting diodes with reducing density of surface
state and leakage current. A passivation layer covering over
surface can reduce the density of the surface state and lower
leakage current.
[0010] Another one of the objectives of the present invention is to
provide light emitting diodes with avoiding current crowding. The
designed shapes of contacts and position arrangement for contacts
can provide the current paths with substantially equal distance
between contacts.
[0011] The present invention provides a light semiconductor device
comprising a substrate and a first semiconductor structure on the
substrate. A light emitting structure is on a first portion of the
first semiconductor structure. A first contact structure is on a
second portion of the first semiconductor structure. The second
portion is separated from the first portion of the first
semiconductor structure. The first contact structure has a first
shape. A second semiconductor structure is on the light emitting
structure. A transparent contact is on the second semiconductor
structure and has a cut-off portion to expose the portion of second
semiconductor structure and a second shape. A second contact
structure is on the cut-off portion of the transparent contact. The
second contact structure contacting the second semiconductor has a
third shape. The second contact structure with the third shape is
corresponded to both the transparent contact with the second shape
and the first contact structure with the first shape whereby a
relationship provides a plurality of current paths with
substantially equal distances between the first contact structure
and the second contact structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A better understanding of the invention may be derived by
reading the following detailed description with reference to the
accompanying drawing wherein:
[0013] FIG. 1 is a diagram of plan view for a conventional
GaN-based LED;
[0014] FIG. 2 is a cross-sectional schematic diagram illustrating a
GaNbased LED grown on an insulating substrate having a contact
structure with current blocking windows to improved current
spreading in accordance with the present invention;
[0015] FIGS. 3-4 are diagrams of plan view for FIG.2 taken along
the line A-A in accordance with the present invention;
[0016] FIG. 5 is a cross-sectional diagram illustrating a
passivation layer covering over the surface of LED for improving
reliability of the device;
[0017] FIGS. 6-8 are multitude diagrams of top view illustrating
the shapes and arrangement for the contacts in accordance with the
present invention;
[0018] FIG. 9 is a diagram of top view for another embodiment
illustrating the n-type contact at a center of LED in accordance
with the present invention; and
[0019] FIG. 10 is the cross-sectional diagram of FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] The semiconductor devices of the present invention are
applicable to a board range of semiconductor devices and can be
fabricated from a variety of semiconductor materials. While the
invention is described in terms of a single preferred embodiment,
those skilled in the art will recognize that many steps described
below can be altered without departing from the spirit and scope of
the invention.
[0021] Furthermore, there is shown a representative portion of a
semiconductor structure of the present invention in enlarged,
cross-sections of the two dimensional views at several stages of
fabrication. The drawings are not necessarily to scale, as the
thickness of the various layers are shown for clarify of
illustration and should not be interpreted in a limiting sense.
Accordingly, these regions will have dimensions, including length,
width and depth, when fabricated in an actual device.
[0022] In a preferred embodiment, the GaN-based device is used for
demonstration. However, it shouldn't be limited to such material
system. The term "GaN-based materials" means the materials made of
Al.sub.XGayIn.sub.(1-X-Y)N where bothXandYis between 0 and
1(0.ltoreq.X.ltoreq.1, 0.ltoreq.Y.ltoreq.1) A GaN-based LED means
the LED with a narrower bandgap GaN-based light-emitting structure
sandwiched between single or multiple layers of a wider bandgap
GaN-based structures with different conductive types on different
sides of the light-emitting structure.
[0023] Moreover, the invention is applicable to LED grown on
nonconductive substrate, such as sapphire. It also can be applied
to the LED on a conductive substrate, such as GaAs, GaP, Si, SiC,
when a vertical conduction configuration is not available.
[0024] The present invention addresses methods of improving current
spreading by means of device geometry and contact design. In the
embodiment, a transparent ohmic contact layer is used on the top of
the side of the device with less conductivity. All the contacts are
carefully designed to minimize the current crowding, maximize the
light-emitting area, and hence improve the efficiency and lifetime
of the LED. Details of the concept of the current invention can be
illustrated as followings. However, it shouldn't be limited to the
following embodiments.
[0025] Depicted in FIG. 2 and FIG. 3, is individually the
cross-sectional and top-view diagrams illustrating the embodiment
of the present invention. An n-type GaN structure 12 is grown on an
insulating substrate 1 1, such as a sapphire substrate 1 1. A light
emitting structure 13 is grown on the n-type GaN structure 12
followed by a p-type GaN structure 14 thereon. Both n-type GaN and
p-type one can be either a single layer, such as GaN, or a multiple
layer, such as a combination GaN, AlN and other combination. The
light emitting structure can be a homogeneous p-n junction, a
double hetero-junction, a single quantum well structure, or a
multiple quantum well structure. The preferred device structure
consists of a single n-type GaN layer, a InGaN/GaN multiple quantum
well light emitting layer, and AlGaN/GaN (at p-side) layer grown on
the sapphire substrate 11. The semiconductor LED is epitaxially
prepared under the above arrangement.
[0026] Next, the epi-wafer is subject to a device processing, which
includes defining a chip by mesa etching, metallization, and
thermal process. The metallization is implemented for a transparent
contact 15 with multitude of hollow patterns 16, p-type contact 17
(an electrode may be included), and n-type ohmic contact 18.
Furthermore, the thermal process is implemented for the oxidation
of the transparent p-type contact 17 and annealing of both p-type
contact 17 and n-type ohmic contact 18. From top-view, the p-type
contact 17 and the n-type ohmic contact 18 are separated, that is,
they are not overlapped at the vertical direction. The transparent
contact 15 can be made by nickel oxide/Au, MgO, ZnO, and
V.sub.2O.sub.5. In the embodiment, nickel oxide/Au is used for the
transparent contact.
[0027] The designed hollow patterns (windows) 16 are the keys of
the present invention, which may have multi-folds functions. First,
the hollow patterns 16 can block current from taking shortcut.
Second, they can serve to even out differences between the shortest
and the longest current paths if they are precisely designed. The
transparent contact 15 is not totally transparent with 100% while
the hollow patterns 16 are acted as optical paths with no thin
metal blocking light from coupling out of the device. The emitting
efficiency of the device is also improved via the patterns 16
(windows) at the same time with better current spreading.
[0028] Furthermore, the shape, number, and position of the patterns
16 of the transparent contacts are not limited to those shown in
the embodiment. It can and should be optimized to any different
type of the current rating and the device applications. The present
invention works most effectively when the p- and n-contacts are
positioned at the opposite sides. FIG. 4, a top-view diagram is
depicted another one example of the present invention applied to a
rectangular shape LED with the p-type contacts 17 and n-type ohmic
contacts 18 positioned at the opposite sides of the rectangle.
[0029] The performance of the device may be further improved by
minimizing the number of the surface states, which is responsible
for the leakage current. The surface states can be greatly reduced
by applying a passivation layer 19 over the device, shown in FIG.
5. Multitude of materials can be implemented for the purpose of the
surface passivation. For a light emitter, the surface passivation
layer has high optical transmission at the emitted wavelength and
iselectrically insulating or highly resistive. Those materials,
such as aluminum oxide, silicon oxide, silicon nitride, tantalum
oxide, titanium oxide, calcium fluoride, hafnium oxide, zinc
sulfide and zinc oxide, may meet the requirement. The passivation
layer also can be applied to any other embodiments of the present
invention, and not be emphasized and mentioned repeatedly.
[0030] FIG. 2 to FIG. 4 are depicted focused on the current
blocking patterns that force the current to spread out more
uniformly. Another geometric approach is used to spread current
uniformly. As shown in FIG. 6 is a top-view diagram illustrating
the improvement of geometric in accordance with the present
invention. The device structure has precisely designed mesa and
contact structures so that the shortest distances between the
contacts are kept same. As mentioned above, the current in a
conventional LED may get crowded between the contacts (or contact
pads) because electrons tend to shortcut their paths, and large
portion of the chip is not efficiently used.
[0031] In the second embodiment, a transparent contact 25, a p-type
contact 27, and an n-type contact 28 are on an n-GaN structure 22.
They are arranged in such way that the distance from any point of
the p-type contact 27 to the n-type contact 28 is the shortest and
kept same for each path. The p-type contact 27 has a quarter-circle
shape, and the transparent contact 25 has a fan shape that has a
same center of the circle as that of the p-type contact 27. The
radial distance of spreaded current is all the same from the p-type
contact 27 to the n-type contact 28 through the transparent contact
25.
[0032] Depicted in FIG. 7 is another one design of the shapes and
arrangements for a p-type contact 37, an n-type contact 38, and a
transparent contact 35 on a mesa structure 32 which is on an n-GaN
structure 33. The p-type contact 37 and the n-type contact 38 are
arranged at the opposite sides rather than the opposite corners.
The shapes of the p-type contact 37 and the n-type contact 38 are
spreaded in two dimensions. The shapes and arrangement also can
build current paths with same and uniform distance between the
n-type and p-type contacts.
[0033] Again, the current spreading and efficient usage of the
lightemitting area is further improved with more symmetrical
contact configuration, shown in FIG. 8. In the embodiment, the
epi-layer structure is the same as that of the first embodiment,
while the shapes of the mesa and contacts are different. A
ring-shape n-type contact 48 is around the device and on the n-type
GaN-based layer 42, both are located at the bottom of the mesa. A
p-type transparent contact 45 is on a p-type GaN-based layer 44 and
the p-type GaN-based layer 44 is at the top of the mesa. For
spreading the current, a p-type contact 47 is positioned at or near
the center of the mesa, and n-type contact 48 has a contact pad and
a conduction ring. The shapes and positions for both contacts (47
and 48) provide all current distances between the contacts equal or
nearly equal all the way around the mesa. Therefore, the device
exhibit good current spreading and high area utility. The shape of
the p-type contact 47 is not limited to the one shown in FIG. 8.
For a small chip with the sizes of 14 mils *14 mils or less, the
shape of the contact may be simpler, such as circular, square with
or without extended fingers, and so on. Such a design also can be
applied to the following embodiment.
[0034] Next is another one embodiment, a top-view diagram shown in
FIG. 9 and a cross-sectional one in FIG. 10. For good conductivity
and carrier mobility of n-type materials, the current spreading
capability of the n-type layer is utilized. An n-type contact 58 is
arranged at or near the center of the device with an inverted mesa
(or well) structure. A p-type transparent contact 55 covers almost
all the rest area of the device, thus may maximize the efficient
light-emitting area. The current spreading is enhanced by a
ring-shape p-type contact 57. In the preferred embodiment, the area
of the p-type transparent contact 55 is larger than one of the
p-type transparent contact 45 of FIG. 8, thus a larger valuable
light-emitting area is provided. Those epi-layers consisting of an
n-type structure 52, light-emitting structure 53 and a p-type
structure 54 are implemented by using same materials as ones in
FIG. 2. The materials of the contacts, such as a transparent
contact 55, an n-type contact 58, and a p-type contact 57 are the
same as ones in FIG. 2. According to this designed structure, the
current is spreaded well with a low contact resistance, and the
lifetime of the transparent contact is prolonged.
[0035] The present invention provides a light emitting diode device
comprising a substrate and a first semiconductor structure on the
substrate. A light emitting structure is on a first portion of the
first semiconductor structure. A first contact structure is on a
second portion of the first semiconductor structure. The second
portion is separated from the first portion of the first
semiconductor structure. The first contact structure has a first
shape. A second semiconductor structure is on the light emitting
structure. A transparent contact is on the second semiconductor
structure and has a cut-off portion to expose the portion of second
semiconductor structure and a second shape. A second contact
structure is on the cut-off portion of the transparent contact. The
second contact structure contacting the second semiconductor has a
third shape. The second contact structure with the third shape is
corresponded to both the transparent contact with the second shape
and the first contact structure with the first shape whereby a
relationship provides a plurality of current paths with
substantially equal distances between the first contact structure
and the second contact structure.
[0036] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons skilled
in the art upon reference to the description. It is therefore
intended that the appended claims encompass any such modifications
or embodiments.
* * * * *