(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`27 November 2008 (27.11.2008)
`
`International Patent Classification:
`H01L 27/15 (2006.01)
`
`
`
`(51)
`
`(21)
`
`(22)
`
`(25)
`
`(26)
`
`(30)
`
`(71)
`
`(72)
`(75)
`
`International Application Number:
`PCT/US2007/O22959
`
`International Filing Date: 3 1 October 2007 (3 1.10.2007)
`
`Filing Language:
`
`Publication Language:
`
`English
`
`English
`
`Priority Data:
`60/885,306
`60/944,611
`
`17 January 2007 (17.01.2007)
`18 June 2007 (1 806.2007)
`
`US
`US
`
`Applicants (for all designated States except US): THE
`BOARD OF TRUSTEES OF THE UNIVERSITY OF
`
`ILLINOIS [US/US]; 352 Henry Administration Bldg,
`506 South Wright Street, Urbana, IL 61801 (US). SEM-
`PRIUS, INC. [US/US]; 2530 Meridian Parkway, Suite
`300, Durham, NC 27713 (US).
`
`Inventors; and
`Inventors/Applicants (for US only): ROGERS, John
`[US/US]; 2803 Valleybrook, Champaign, IL 61822 (US).
`NUZZO, Ralph [US/US]; 2413 Nottingham Court North,
`Champaign, IL 61821 (US). MEITL, Matthew [US/US];
`8100 L4 Stonebrook Terrace, Raleigh, NC 27617 (US).
`MENARD, Etienne [FR/US]; 5215 Newhall Rd., Durham,
`
`(74)
`
`(81)
`
`(10) International Publication Number
`
`WO 2008/143635 A1
`
`NC 27713 (US). BACA, Alfred, J. [US/US]; 1601 South
`Bermuda Drive, Urbana,
`IL 61802 (US). MOTALA,
`lVIichael [CA/US]; 405 West Washington Street, Main
`Floor, Champaign,
`IL 61820 (US). AHN, Jong-Hyun
`[KR/US]; 803 E. Oakland Avenue, #202, Urbana,
`IL
`61802 (US). PARK, Sang-I]
`[KR/US];
`107—c West
`Tomaras Avenue, Savoy, IL 61874 (US). YU, Chang-Jae
`[KR/US]; 1020 E. Kerr Ave., #201, Urbana, IL 61802
`(US). KO, Heung, C110 [KR/US]; 300 S. Goodwin Ave.,
`#515, Urbana, IL 61801 (US). STOYKOVICH, lVIark
`[US/US]; 35 Westwood Circle, Dover, NH 03820—4321
`(US). YOON, Jongseung [KR/US]; 1107 West Green St.,
`Apt. 627, Urbana, IL 61801 (US).
`Agents: BARONE, Stephen, B. et 211.; Greenlee, Winner
`And Sullivan, P.c., 4875 Pearl East Circle, Suite 200, Boulr
`der, CO 80301 (US).
`
`Designated States (unless otherwise indicated, for every
`kind ofnational protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BH, BR. BW, BY, BZ, CA, CH,
`CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE, EG,
`ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL,
`IN, IS, JP, KE, KG, KM, KN, KP, KR, KZ, LA, LC, LK,
`LR, LS, LT, LU, LY, MA, MD, ME, MG, MK, MN, MW,
`MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PG, PH, PL,
`PT, RO, RS, RU, SC, SD, SE, SG, SK, SL, SM, SV. SY,
`
`[Continued on next page]
`
`(54) Title: OPTICAL SYSTEMS FABRICATED BY PRINTING—BASED ASSEMBLY
`
`
`
`Diffusing optics
`
`LED
`
`Polymer or other low-
`cost substrate
`
`Fig. 23
`
`
`
`Optical fiber
`
`III-V VCSEL
`
`Silicon lC chip
`
`
`
`08/143635A1|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
`
`(57) Abstract: The present invention provides optical devices and systems fabricated, at least in part, via printing—based assem—
`c bly and integration of device components Optical systems of the present invention comprise semiconductor elements assembled,
`N organized and/or integrated with other device components via printing techniques that exhibit performance characteristics and func—
`tionality comparable to 10 single crystalline semiconductor based devices fabricated using conventional high temperature processing
`methods Optical systems of the present invention have device geometries and configurations, such as form factors, component den—
`sities, and component positions, accessed by printing that provide a range of useful device functionalities.
`
`W0
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`WO 2008/143635 A1
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`|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
`
`TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA,
`ZM, ZW,
`
`PT, RO, SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM,
`GA, GN, GQ, GW, NIL, IVIR, NE, SN, TD, TG).
`
`(84) Designated States (unless otherwise indicated, for every
`Published:
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM, — with international search report
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), — before the expiration of the time limit for amending the
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,
`claims and to be republished in the event of receipt of
`FR, GB, GR, HU, IE, IS, IT, LT, LU, LV, MC, MT, NL, PL,
`amendments
`
`

`

`WO 2008/143635
`
`PCT/U52007/022959
`
`OPTICAL SYSTEMS FABRICATED BY PRINTING-BASED ASSEMBLY
`
`CROSS-REFERENCE TO RELATED APPLICATIONS
`
`[001]
`
`This application claims the benefit of priority to U.S. Provisional Patent
`
`Applications 60/885,306 filed January 17, 2007 and 60/944,611 filed June 18, 2007,
`
`both of which are hereby incorporated by reference in their entirety to the extent not
`
`inconsistent with the disclosure herein.
`
`STATEMENT REGARDING FEDERALLY SPONSORED
`
`. RESEARCH OR DEVELOPMENT
`
`[002]
`
`This invention was made, at least in part, with United States governmental
`
`support under DEFGO2-91-ER45439 awarded by U.S. Department of Energy. The
`
`United States Government has certain rights in this invention.
`
`BACKGROUND OF INVENTION
`
`[003]
`
`Since the first demonstration of a printed, all polymer transistor in 1994, a great
`
`deal of interest has been directed at development of a new class of electronic systems
`
`comprising flexible integrated electronic devices on plastic substrates. [Garnier, F.,
`
`Hajlaoui, R., Yassar, A. and Srivastava, P., Science, Vol. 265, pgs 1684— 1686]
`
`Substantial research has been directed over the last decade toward developing new
`
`solution processable materials for conductors, dielectrics and semiconductors elements
`
`for flexible polymer-based electronic devices. Progress in the field of flexible electronics
`is not only driven by the development of new solution processable materials but also by
`
`new device geometries, techniques for high resolution, dense patterning of large
`
`substrate areas, and high throughput processing strategies compatible with plastic
`
`substrates.
`It is expected that the continued development of new materials, device
`configurations and fabrication methods vVill play an essential role in the rapidly emerging
`
`new class of flexible integrated electronic devices, systems and circuits.
`
`[004]
`
`Interest in the field of flexible electronics arises out of several important
`
`advantages provided by this technology. First, the mechanical ruggedness of plastic
`
`substrates provides a platform for electronic devices less susceptible to damage and/or
`
`electronic performance degradation caused by mechanical stress. Second, the inherent
`
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`PCT/US2007/022959
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`7
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`7
`7
`wo 2008/143635
`tIeXIbIlIty and deformablllty of plastic substrate materlals allows these materials to be
`
`integrated into useful shapes, form factors and configurations not possible with
`
`conventional brittle silicon based electronic devices. For example, device fabrication on
`
`flexible, shapeable and/or bendable plastic substrates has potential to enable a class of
`
`functional devices having revolutionary functional capabilities, such as electronic paper,
`
`wearable computers, large-area sensors and high resolution displays, that are not
`
`feasible using established silicon-based technologies. Finally, electronic device
`
`assembly on flexible plastic substrates has potential for low cost commercial
`
`implementation via high speed processing techniques, such as printing, capable of
`
`assembling electronic devices over large substrate areas.
`
`[005] Despite considerable motivation to develop a commercially feasible platform for
`
`flexible electronics, the design and fabrication of flexible electronicldevices exhibiting
`
`good electronic performance continues to present a number of significant technical
`
`challenges. First, conventional well-developed methods of making single crystalline
`
`silicon based electronic devices are incompatible with most plastic materials. For
`
`example, traditional high quality inorganic semiconductor components, such as single
`
`crystalline silicon or germanium semiconductors, are typically processed by growing thin
`
`films at temperatures (> 1000 degrees Celsius) that significantly exceed the melting or
`
`decomposition temperatures of most or all plastic substrates.
`
`In addition, many
`
`inorganic semiconductors are not intrinsically soluble in convenient solvents that would
`
`allow for solution based processing and delivery. Second, although amorphous silicon,
`
`organic or hybrid organic-inorganic semiconductors have been developed that are
`
`compatible with low temperature processing and integration into plastic substrates,
`
`these materials do not exhibit electronic properties comparable to conventional single
`
`crystalline semiconductor based systems. Accordingly, the performance of electronic
`
`devices made from these alternative semiconductor materials is less than current state
`
`of the art high performance semiconductor devices. As a result of these limitations,
`
`flexible electronic systems are presently limited to specific applications not requiring
`
`high performance, such as use in switching elements for active matrix flat panel displays
`
`with non-emissive pixels and in light emitting diodes.
`
`[006] Macroelectronics is a rapidly expanding area of technology which has
`
`generated considerable interest in developing commercially feasible flexible electronic
`
`systems and processing strategies. The field of macroelectronics relates to
`
`microelectronic systems wherein microelectronic devices and device arrays are
`
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`PCT/US2007/022959
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`distributed and integrated on large area substrates significantly exceeding the physical
`
`dimensions of conventional semiconductor wafers. A number of macroelectronic
`
`products have been successfully commercialized including large area macroelectronic
`
`flat panel display products. The majority of these display systems comprise amorphous
`
`or polycrystalline silicon thin film transistor arrays patterned onto rigid glass substrates.
`
`Macroelectronic display devices having substrate dimensions as large as 100’s of
`
`meters squared have been achieved. Other macroelectronic products in development
`
`include photovoltaic device arrays, large area sensors and RFID technology.
`
`10
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`
`[007] Despite considerable progress in this field, there is continued motivation to
`
`integrate flexible substrates and device structures into macroelectronic systems so as to
`
`impart new device functionality, such as enhanced ruggedness, mechanical flexibility
`
`and bendability. To address this need, a number material strategies for flexible
`
`macroelectronic systems are currently being pursued including organic semiconductor
`
`thin film transistor technology, nano-wire and nanoparticle based flexible electronics and
`
`organic/inorganic semiconductor hybrid technology.
`
`In addition, substantial research is
`
`currently directed at developing new fabrication processes for accessing high
`
`throughput and low cost manufacturing of macroelectronic systems.
`
`[008] US. Patents 11/145,574 and 11/145,542, both filed on June 2, 2005, disclose a
`
`high yield fabrication platform using printable semiconductor elements for making
`
`electronic devices, optoelectronic devices and other functional electronic assemblies by
`
`versatile, low cost and high area printing techniques. The disclosed methods and
`
`compositions provide for the transfer, assembly and/or and integration of microsized
`
`and/or nanosized semiconductor elements using dry transfer contact printing and/or
`
`solution printing techniques providing good placement accuracy, registration and pattern
`
`fidelity over large substrate areas. The disclosed methods provide important processing
`
`advantages enabling the integration of high quality semiconductor materials fabricated
`
`using conventional high temperature processing methods onto substrates by printing
`
`techniques which may be independently carried out at relatively low temperatures (<
`
`about 400 degrees Celsius) compatible with a range of useful substrate materials,
`
`including flexible plastic substrates. Flexible thin film transistors fabricated using
`
`printable semiconductor materials exhibit good electronic performance characteristics,
`
`such as device field effect mobilities greater than 300 cm2 V'1 s"1 and on/off ratios
`greater than 103, when in flexed and non-flexed conformations.
`-
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`_ PCT/US2007/022959
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`wo zoos/143635
`[009]
`It Will be apprecrated from the foregorng that a need exnsts for methods of
`
`making large area integrated electronics, including macroelectronic systems.
`
`In
`
`particularly, fabrication methods for these systems are needed that are capable of high-
`
`throughput and low cost implementation. Further, there is currently a need for
`
`macroelectronic systems combining good electronic device performance and enhanced
`
`mechanical functionality such as flexibility, shapeability, bendability and/or stretchability.
`
`SUMMARY OF THE INVENTION
`
`[010]
`
`The present invention provides optical devices and systems fabricated, at least
`
`10
`
`in part, via printing-based asSembly and integration of printable functional materials
`
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`and/or semiconductor-based devices and device components.
`In specific embodiments
`the present invention provides light emitting systems, light collecting systems, light
`
`sensing systems and photovoltaic systems comprising printable semiconductor
`
`elements, including large area, high performance macroelectronic devices. Optical
`
`systems of the present invention comprise printable semiconductor containing structures
`
`(e.g., printable semiconductor elements) assembled, organized and/or integrated with
`
`other device components via printing techniques that exhibit performance characteristics
`
`and functionality comparable to single crystalline semiconductor based devices
`
`fabricated using conventional high temperature processing methods. Optical systems
`
`of the present invention have device geometries and configurations, such as form
`
`factors, component densities, and component positions, accessed by printing that
`
`provide a range of useful device functionalities. Optical systems of the present
`
`invention include devices and device arrays exhibiting a range of useful physical and
`
`mechanical properties including flexibility, shapeability, conformability and/or
`
`stretchablity. Optical systems of the present invention include, however, devices and -
`I device arrays provided on conventional rigid or semi-rigid substrates, in addition to
`
`devices and device arrays provided on flexible, shapeable and/or stretchable substrates.
`
`[011]
`
`This invention also providesdevice fabrication and processing steps, methods
`
`and materials strategies for making optical systems at least in part via printing
`
`techniques, including contact printing, for example using a conformable transfer devices,
`
`such as an elastomeric transfer device (e.g., elastomer layer or stamp).
`In specific
`embodiments, methods of the present invention provide a high-throughput, low cost
`
`fabrication platform for making a range of high performance optical systems, including
`
`light emitting systems, light collecting systems, light sensing systems and photovoltaic
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`PCT/US2007/022959
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`systems. Processing provided by the present methods is compatible with large area
`
`substrates, such as device substrates for microelectronic devices, arrays and systems.
`
`and is useful for fabrication applications requiring patterning of layered materials, such
`as patterning printable structures and/or thin film layers for electronic and electro-optic
`
`devices. Methods of the present invention are complementary to conventional
`
`microfabrication and nanofabrication platforms, and can be effectively integrated into
`
`existing photolithographic, etching and thin film deposition device patterning strategies,
`
`systems and infrastructure. The present device fabrication methods provide a number
`
`of advantages over conventional fabrication platforms including the ability to integrate
`
`very high quality semiconductor materials, such as single crystalline semiconductors
`
`and semiconductor-based electronic devices/device components, into optical systems
`
`provided on large area substrates, polymer device substrates, and substrates having
`
`contoured a conformation.
`
`[012]
`
`In an aspect, the present invention provides processing methods using high
`
`quality bulk semiconductor wafer starting materials that are processed to provide large
`
`yields of printable semiconductor elements with preselected physical dimensions and
`
`shapes that may be subsequently transferred, assembled and integrated into optical
`
`systems via printing. An advantage provided by the present printing-based device
`
`fabrication methods is that the printable semiconductor elements retain desirable
`
`electronic properties, optical properties and compositions of the high quality bulk water
`
`starting material (e.g., mobility, purity and doping etc.) while having different mechanical
`
`properties (e.g., flexibility, stretchability etc.) that are useful for target applications such
`
`as flexible electronics.
`
`In addition, use of printing-based assembly and integration, for
`
`example via contact printing or solution printing, is compatible with device fabrication
`
`over large areas, including areas greatly exceeding the dimensions of the bulk wafer
`
`starting material. This aspect of the present invention is particularly attractive for
`
`applications in macroelectronics. Further, the present semiconductor processing and
`
`device assembly methods provide for very efficient use of virtually the entire starting
`semiconductor material for making printable semiconductor elements that can be
`
`assembled and integrated into a large number of devices or device components. This
`
`aspect of the present invention is advantageous because very little of the high quality
`
`semiconductor wafer starting material is wasted or discarded during processing, thereby
`
`providing a processing platform capable of low cost fabrication of optical systems.
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`[013]
`In one aspect, the present Invention provrdes optical systems compnsrng
`
`printable semiconductor elements, including printab|e semiconductor-based electronic
`
`devices/device components, assembled, organized and/or integrated using contact
`
`printing.
`
`In an embodiment of this aspect, the invention provides a semiconductor-
`
`based optical system made by a method comprising the steps of: (i) providing a device
`
`substrate having a receiving surface; and (ii) assembling one or more plurality of
`
`printable semiconductor elements on the receiving surface of the substrate via contact
`
`printing.
`
`In an embodiment, the optical system of this aspect of the present invention
`
`comprises an array of semiconductor-based devices or device components assembled
`
`on the receiving surface of the substrate via contact printing.
`
`In specific embodiments,
`
`each of the printable semiconductor elements of the optical system comprises a
`
`semiconductor structure having a length selected from the range of 0.0001 millimeters
`
`to 1000 millimeters, a width selected from the range of 0.0001 millimeters to 1000
`
`millimeters and a thickness selected from the range of 0.00001 millimeters to 3
`
`millimeters.
`
`In an embodiment of this aspect, printable semiconductor elements
`
`comprise on or more semiconductor devices selected from the group consisting of LED,
`
`solar cell, diode, p-n junctions, photovoltaic systems, semiconductor-based sensor,
`
`laser, transistor and photodiode, having a length selected from the range of 0.0001
`millimeters to 1000 millimeters, a'width selected from the range of 0.0001 millimeters
`
`to 1000 millimeters and a thickness selected from the range of 0.00001 millimeters to
`
`3 millimeters.
`
`In an embodiment, the printable semiconductor element comprises a
`
`semiconductor structure having a length selected from the range of 0.02 millimeters to
`
`30 millimeters, and a width selected from the range of 0.02 millimeters to 30
`
`millimeters, preferably for some applications a length selected from the range of 0.1
`
`millimeters to 1 millimeter, and a width selected from the range of 0.1 millimeters to 1
`
`millimeter, preferably for some applications a length selected from the range of
`
`1
`
`millimeters to 10 millimeters, and a width selected from the range of
`
`1 millimeter to 10
`
`millimeters.
`
`In an embodiment, the printable semiconductor element comprises a
`
`semiconductor structure having a thickness selected from the range of 0.0003
`
`millimeters to 0.3 millimeters, preferably for some applications a thickness selected
`
`from the range of 0.002 millimeters to 0.02 millimeters.
`
`In an embodiment, the
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`printable semiconductor element comprises a semiconductor structure having a length
`
`. selected from the range of 100 nanometers to 1000 microns. a width selected from the
`
`range of 100 nanometers to 1000 microns and a thickness selected from the range of
`
`35
`
`10 nanometers to 1000 microns.
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`[014]
`In an embodiment, the printable semiconductor element(s) is/are an electronic
`
`device or a component of an electronic device.
`
`In an embodiment, the printable
`
`semiconductor element(s) is/are selected from the group consisting of: an LED, a laser,
`
`a solar cell, a sensor, a diode, a transistor, and a photodiode.
`
`in an embodiment, the
`
`printable semiconductor element(s) comprises the semiconductor structure integrated
`
`with at least one additional structure selected from the group consisting of: another
`
`semiconductor structure; a dielectric structure; conductive structure, and an optical
`
`structure.
`
`In an embodiment, the printable semiconductor element comprises the
`
`semiconductor structure integrated with at least one electronic device component
`
`selected from the group consisting of: an electrode, a dielectric layer, an optical coating,
`
`a metal contact pad and a semiconductor channel.
`
`In an embodiment, the system
`
`further comprises an electrically conducting grid or mesh provided in electrical contact
`
`with at least a portion of said printable semiconductor elements, wherein the electrically
`
`conducting grid or mesh providing at least one electrode for said system.
`
`[015]
`
`Useful contact printing methods for assembling, organizing and/or integrating
`
`printable semiconductor elements of this aspect include dry transfer contact printing,
`
`microcontact or nanocontact printing, microtransfer or nanotransfer printing and self
`
`assembly assisted printing. Use of contact printing is beneficial in the present optical
`
`systems because it allows assembly and integration of a plurality of printable
`
`semiconductor‘in selected orientations and positions relative to each other. Contact
`
`printing in the present invention also enables effective transfer, assembly and
`
`integration of diverse classes of materials and structures, including semiconductors
`
`(e.g., inorganic semiconductors, single crystalline semiconductors, organic
`
`semiconductors, carbon nanomaterials etc.), dielectrics, and conductors. Contact
`
`printing methods of the present invention optionally provide high precision registered
`
`transfer and assembly of printable semiconductor elements in preselected positions and
`
`spatial orientations relative to one or more device components prepatterned on a device
`
`substrate. Contact printing is also compatible with a wide range of substrate types,
`
`including conventional rigid or semi-rigid substrates such as glasses, ceramics and
`
`metals, and substrates having physical and mechanical properties attractive for specific
`
`applications, such as flexible substrates, bendable substrates, shapeable substrates,
`
`conformable substrates and/or stretchable substrates. Contact printing assembly of
`
`printable semiconductor structures is compatible, for example, with low temperature
`
`processing (e.g., less than or equal to 298K). This attribute allows the present optical
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`systems to be Implemented usrng a range of substrate materials including those that
`
`decompose or degrade at high temperatures, such as polymer and plastic substrates.
`
`Contact printing transfer, assembly and integration of device elements is also beneficial
`
`because it can be implemented via low cost and high-throughput printing techniques
`
`and systems, such as roll-to-roll printing and flexographic printing methods and systems.
`
`The present invention include methods wherein contact printing is carried out using a
`
`conformable transfer device, such as an elastomeric transfer device capable of
`
`establishing conformal contact with external surfaces of printable semiconductor
`
`elements. .In embodiments useful for some device fabrication applications contact
`
`10
`
`printing is carried out using an elastomeric stamp.
`
`In an embodiment, the step of contact printing-based assembly of printable
`[016]
`semiconductor comprises the steps of:
`(i) providing a conformable transfer device
`
`having one or more contact surfaces;
`
`(ii) establishing conformal contact between an
`
`external surface of the printable semiconductor element and the contact surface of the
`
`conformable transfer device, wherein the conformal contact bonds the printable
`
`semiconductor element to the contact surface;
`
`(iii) contacting the printable
`
`semiconductor element bonded to the contact surface and the receiving surface of the
`
`device substrate; and (iv) separating the printable semiconductor element and the
`
`contact Surface of the conformable transfer device, thereby assembling the printable
`
`semiconductor element on the receiving surface of the device substrate.
`
`In some
`
`embodiments, the step of contacting the printable semiconductor element bonded to the
`
`contact surface and the receiving surface of the device substrate comprises establishing
`conformal contact between the contact surface of the transfer device having the
`
`printable semiconductor element(s) and the receiving surface.
`
`In some embodiments,
`
`the printable semiconductor element(s) on the contact surface are brought into contact
`
`with an adhesive and/or planarizing layer provided on the receiving surface to facilitate
`
`release and assembly on the device substrate. Use of elastomeric transfer devices,
`
`such as elastomer layers or stamps including PDMS stamps and layers, is useful in
`
`some methods given the ability of these devices to establish conformal contact with
`
`printable semiconductor elements, and the receiving surfaces, external surface and
`
`internal surfaces of device substrates and optical components.
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`[017] Use of printable semiconductor materials and printable semiconductor-based
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`electronic devices/device components in embodiments of this aspect provides the
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`capable of integrating a range of high quality semiconductor materials for fabricating
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`PICT/U.S2007/022959
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`WO 2008/143635
`optical systems exhibiting excellent devrce performance and functionality. Useful
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`printable semiconductor elements include, semiconductor elements derived from high
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`quality semiconductor wafer sources, including single crystalline semiconductors,
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`polycrystalline semiconductors, and doped semiconductors.
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`In a system of the present
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`invention, the printable semiconductor element comprises a unitary inorganic
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`semiconductor structure. In a system of the present invention, the printable
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`semiconductor element comprises a single crystalline semiconductor material.
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`In
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`addition, use of printable semiconductor structures provides the capability of integrating
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`printable structures comprising semiconductor electronic, optical and opto-electronic
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`devices, device components and/or semiconductor heterostructures, such as hybrid
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`materials made via high temperature processing and subsequently assembled on a
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`substrate via printing.
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`In certain embodiment, printable semiconductor elements of the
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`present invention comprise functional electronic devices or device components, such as
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`p-n junctions, semiconductor diodes, light emitting diodes, semiconductor lasers (e.g.,
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`Vertical-Cavity Surface-Emitting Lasers (VCSEL)), and/or photovoltaic cells.
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`[018]
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`In an. embodiment, the printable semiconductor elements are assembled on said
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`device substrate such that they generate a multilayer structure on said receiving
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`surface.
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`In an embodiment, for example, the multilayer structure comprises
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`mechanically-stacked solar cells.
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`In an embodiment, for example, the printable
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`semiconductor elements are solar cells having different band-gaps.
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`[019]
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`Optical systems of this aspect of the present invention may optionally comprise
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`a variety of additional device elements including, but not limited to, optical components,
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`dielectric structures, conductive structures, adhesive layers or structures, connecting
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`structures, encapsulating structures, planarizing structures, electro-optic elements
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`and/or thin film structures and arrays of these structures.
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`In an embodiment, for
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`example, an optical system of the present invention further comprises one or more
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`passive or active optical components selected from the group consisting of: collecting
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`optics, concentrating optics, diffusing optics, dispersive optics, optical fibers and arrays
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`thereof, lenses and arrays thereof, diffusers, reflectors, Bragg reflectors, waveguides
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`(“light-pipes”), and optical coatings (e.g., reflective coatings or antireflective coatings).
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`In some embodiments, active and/or passive optical components are spatially aligned
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`with respect to at least one of the printable semiconductor elements provided on the
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`device substrate. Optical systems of this aspect of the present invention may optionally
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`comprise a variety of additional device components including, but not limited to,
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`electrical interconnects, electrodes, insulators and electro-optical elements. Printed-
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`based assembly may be used to assembly and integrate additional device elements and
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`additional device components, in addition to assembly and integration of these
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`additional elements by variety of techniques well known in the field of microelectronics,
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`including but not limited to, optical photolithography, deposition techniques (e.g.,
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`chemical vapor deposition, physical vapor deposition, atomic layer deposition, sputtering
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`deposition etc.), soft lithography, spin coating and laser ablation patterning.
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`[020]
`Printing-based assembly provides a very high degree of control over the
`physical dimensions, geometry, relative spatial orientation and organization, doping
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`10
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`levels and materials purity of the printable semiconductor elements assembled and
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`integrated into the present optical systems.
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`In an embodiment, printable semiconductor
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`elements of the optical system are provided on the receiving surface of the substrate
`with a density equal to or greater than 5 semiconductor elements mm“, preferably for
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`some embodiments a density equal to or greater than 50 semiconductor elements mm",
`and preferably for some applications a density equal to or greater than 100
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`semiconductor elements mm".
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`In another embodiment, the printable semiconductor
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`elements of the optical system have at least one longitudinal physical dimension (e.g.,
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`length, width etc.), optionally two longitudinal physical dimensions, less than or equal to
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`2000 nanometers, and in some embodiments less than or equal to 500 nanometers. In
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`another embodiment, each printable semiconductor element of the optical system has at
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`least one cross-sectional physical dimension (e.g. thickness) less than or equal to 100
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`microns, preferably for some applications less than or equal to 10 microns, and
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`preferably for some applications less than or equal to 1 microns.
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`In another
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`embodiment, the positions of the printable semiconductor elements in the optical system
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`relative to each other are selected to within 10,000 nanometers.
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`[021]
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`Printable semiconductor elements may be assembled in selected orientations
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`with respect to each other or other device elements of optical systems of the present
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`invention.
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`In an embodiment, printable semiconductor elements of the optical system
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`are longitudinal aligned with respect to each other. The present invention includes, for
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`example, optical systems wherein printable semiconductor elements extend lengths that
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`are parallel to within 3 degrees of each other.
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`in another embodiment, the optical
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`system further comprising first and second electrodes provided on