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Mar 4th, 2014
X-Celeprint: a closer look
On Jan 24th X-Celeprint Ltd., a wholly-owned subsidiary of XTRION N.V. commenced business operations. I-Micronews thought an interview with CTO Christopher Bower would be of interest for our readers.
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Yole Développement: Dr. Bower, before we take a look at X-Celeprint how about a little background on your career thus far. 
Christopher Bower: As a physics graduate student at UNC-Chapel Hill and as a post-doc at Bell Labs, I worked on carbon nanotubes. My first position after my post doc was at start-up InPlane Photonics. In 2003 I joined RTI International in Research Triangle Park (RTP), N.C., where I began working in advanced packaging and 3D integration. In 2007 I joined Semprius Inc., which was spun out of the University of Illinois, Urbana-Champaign (UIUC) to commercialize a process called “micro-transfer-printing (μTP).” In μTP, an elastomer stamp is used to transfer devices from their native substrate onto a non-native substrate. Since the device only contacts the soft elastomer stamp, μTP is a good way to assemble devices that are too thin, small or fragile to be handled using vacuum collets. I was very drawn to this technology because it enables 3D heterogeneous integration of mature compound semiconductor devices, such as lasers or LEDs, onto silicon integrated circuit wafers or onto large-area, low-cost substrates such as glass or plastic. Having spent the last seven years working on μTP, I continue to believe it offers many key advantages in applications that benefit from heterogeneous integration and I am very excited to be part of X-Celeprint.

YD: We understand that X- Celeprint is a subsidiary of XTRION. What is the Xtrion group, who else is part of the group, and how does X-Celeprint fit into their business plans?
CB: Xtrion has holdings in a number of semiconductor and MEMS companies across the globe.  Notably, it is the parent company of X-FAB, the largest European pure-play semiconductor foundry. We certainly see a lot of synergy between what our technology offers regarding heterogeneous integration and X-FAB’s position as a ‘More than Moore’ foundry.

YD: We understand that X-Celeprint will be focused on commercializing micro- transfer printing (μTP) technology developed at Semprius Inc. [ see “Semprius – Massively parallel pick and place: a closer look” ]. Can you explain μTP , exactly what has been licensed and where X-Celeprint will be focusing the technology? 
CB: First, let me clarify that the μTP technology was originally developed at UIUC and then further developed at Semprius. In essence, μTP is a process in which a structured elastomer print-head or stamp is used to transfer microscale semiconductor devices from their native substrates onto non-native substrates.

 Schematic cartoon depicting the Micro-Transfer-Printing process

X-Celeprint has acquired the exclusive rights, from both UIUC and Semprius, to be the sole licensor of μTP technology in a wide range of applications. Semprius will retain the rights to μTP in photovoltaic applications. X-Celeprint will focus on applications in which μTP provides some key advantages versus standard assembly methods.  In general, this means applications that require manipulation of devices that are either too small, fragile or numerous to be effectively handled using vacuum collets and pin tape-ejectors.

YD: Who else is on the X-Celeprint management team?
CB: Kyle Benkendorfer is the CEO. Kyle previously led Semprius business development in non-photovoltaic applications. David Kneeburg is our Chief Systems Engineer. David also comes from Semprius, where he led the effort to design and build μTP tools. Rudi de Winter, CEO of X-FAB, is a company director. Finally, Professor John Rogers, inventor of the technology at UIUC, is a founder of X-Celeprint who serves as a technical advisor.

YD: What does X-Celeprint see as the sweet spot for this technology?
In my view, the sweet spot for μTP will be applications for which standard assembly methods like pick-and-place, and layer-transfer methods like wafer-bonding, have serious shortcomings. In other words, μTP is ideally suited for the manipulation of objects that are too numerous, small, fragile or expensive to manipulate using standard assembly processes. Regarding actual application areas, we are seeing a great deal of interest in heterogeneously integrated photonic components such as lasers and LEDs.

YD: What applications have been examined so far and what results have been achieved?
CB: The most mature application of the technology is printed multi-junction solar cells that are the heart of Semprius Concentrator Photovoltaic (CPV) modules. Semprius has announced a pilot factory where μTP is utilized to transfer the high efficiency solar cells from their native gallium arsenide (GaAs) substrates onto low-cost sub-mount wafers. These printed micro-cells are at the heart of the >35-percent-efficient Semprius production modules .

In addition to the solar application, Semprius was involved in several joint development programs aimed at developing electronic backplanes for active-matrix OLED displays (AMOLEDs). In this work, a process was developed for making printable silicon integrated circuits. The idea was that a single small integrated circuit could drive a cluster of display pixels, so imagine a cluster of 12 or 24 pixels in which a fan-out redistribution metal level connects the small integrated circuit to the pixels. In one three-month span in 2010, Semprius printed more than 10 million of these pixel-driver integrated circuits. Within these backplane programs, Semprius demonstrated that μTP yields could exceed 99.9 percent with a placement accuracy of +/- 1.5um, 3 sigma [C. Bower et al., “Transfer-Printed Integrated Circuits for Display Backplanes,” Proc. Intl. Display Workshop (IDW’10), pg. 1203, 2010].

I would also like to briefly mention the application of micro-transfer-printed lasers. In 2012, Tyndall Institute, Semprius and Seagate published a paper demonstrating a wafer-level process for making III-V lasers on silicon [J. Justice et al. “Wafer-scale integration of group III–V lasers on silicon using transfer printing of epitaxial layers,” Nature Photonics, 2012].  In this work, μTP was used to assemble arrays of small (100 µm x 400 µm) coupons of laser “epitaxy” directly onto a silicon wafer.  Following the μTP, the epitaxy coupons were processed into etched-facet lasers.

Electron micrograph of a microscale Silicon integrated circuit (350 µm x 60 µm x 9 µm) printed onto glass and a Gallium Arsenide laser printed onto Silicon.

YD: μTP requires special hardware, so where will this hardware be coming from?
X-Celeprint will design, sell and support μTP equipment. We have experience designing hardware for both wafer-to-wafer and wafer-to-panel applications, and we are accustomed to modifying the tools to an end-user’s specific application.

Photograph of a wafer-to-panel Micro-Transfer-Printing tool

YD: We see that X-Celeprint has joined the Tyndall National Institutes Irish Photonics Integration Centre (IPIC). What is the purpose of this group and what will X-Celeprint be doing there?
The purpose of IPIC is to stimulate the photonics industry in Ireland. In addition to Tyndall and the other institutes, the center includes at least 18 industry partners and a third of the initial €30M funding comes from these industry partners. The center is set up with ‘‘platform technologies” that all of the industry partners can access, and also company-specific programs that would not necessarily be available to the entire IPIC community. X-Celeprint is participating in IPIC in both ways, meaning the μTP technology is accessible to the entire IPIC community, but will also be included in customer-specific projects. In IPIC, our expectation is that μTP will be used primarily for the heterogeneous integration of optoelectronic devices such as lasers and LEDs.

YD: Will you be working with any other institutes or Universities to further develop the technology base?
Yes. In addition to our operations in Ireland, we have established a µTP capability within RTI International located in Research Triangle Park, North Carolina.  This facility is well known for its expertise in wafer-level back-end processing. This facility is very flexible regarding wafer sizes and materials, and is a really great fit as our U.S. demo facility for µTP.

Also, with Professor Rogers as a founder and advisor, we continue to have strong ties to the academic community and a good working relationship with UIUC. Every year, we see more publications from research groups utilizing transfer-printing to make interesting new devices. We want to be ready and available to help those researchers as they attempt to commercialize their new devices that utilize our μTP technology.

YD: Any commercial customers showing interest? Can you share who and for what application?
There is commercial interest in the technology but, as you could guess, at this time I cannot share any company names. However, we anticipate some announcements in the near future.

YD: Thanks for your time and best of luck to X-Celeprint.



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