Ensuring Stuttgart University's Continuous Relevance

FOUNDED IN 1829, THE INSTITUTION PREVIOUSLY KNOWN AS REALE und Gewerbeschule (Consolidated Real and Trade School) had humble beginnings as a trade school in Stuttgart, Germany. Its fields of study included mechanical engineering, construction, metalwork, drafting, and applied physics. With the industrial revolution in full swing, the school prepared its students to enter the workforce directly with a solid foundation in both practical and theoretical knowledge. It also prepared students to pursue further education at universities in Germany and beyond.

Early in the 20th century, the school expanded its scope to become the Stuttgart Institute of Technology (Technische Hochschule Stuttgart) and evolved from there into a full-fledged university in 1967, the University of Stuttgart (Universität Stuttgart). It has become one of the top learning institutions in Europe, with a strong focus on advanced and applied technology.

With nearly 21,000 students enrolled in 62 bachelor's and 99 master's programs, the university employs 269 professors, 34 junior professors, and hundreds of other scientific staff, including PhD and postdoctor candidates.

The University of Stuttgart has gained a solid reputation for its interdisciplinary approach, which combines engineering, natural sciences, humanities, and social sciences. This helps to build not only specialists in niche areas of study, but critical thinkers who can solve complex problems by drawing from multiple disciplines.

The school has 10 distinct faculties that oversee approximately 150 different institutes, each with specialized fields of study. One example is the Institut für Großflächige Mikroelektronik (IGM), known in English as the Institute for Large Area Microelectronics. Since 1990, IGM has been operating a 500 m² clean room fully equipped for producing active-matrix displays and sensor array demonstrators using near-industrial processes (Fig. 1).

The IGM focuses on the implementation of microelectronics—very small, sometimes microscopic, electronic devices and components—on large surface areas. Its specific fields of commercial application include flat-panel display devices and “smart surfaces,” as well as modulators and filters for optical signal processing. Smart surfaces include any engineered surface that can sense and respond to various stimuli, such as touch, light, proximity, pressure, humidity, and temperature. This technology is not limited to traditional display screens or smart glass, but can be integrated into virtually any solid surface, such as walls, floors, control panels, or even pavement or sidewalks.

Norbert Fruehauf attended the University of Stuttgart, earning his PhD (Dr-Ing.) in electrical engineering. He has more than 30 years of experience in designing and characterizing liquid crystal light modulators and displays. After completing his degree, Fruehauf worked for Physical Optics Corporation (POC), now part of Mercury Systems, in Torrance, California. Here he developed tunable micro-optic components, various display systems, and integrated optical components. In 2001, Fruehauf returned to Germany and was appointed as a full professor, heading what is now IGM. He currently specializes in large-area microelectronics for applications in flexible displays, active-matrix displays (AMOLED and AMLCD), as well as sensor arrays (Fig. 2).

Fruehauf invented the active-matrix OLED pixel circuit with external compensation. This system uses a thin-film transistor (TFT) backplane to control individual OLED pixels, along with a compensation mechanism that uses external circuitry to correct for variations in TFTs and OLEDs, ensuring uniform brightness, color, and image quality across the display and uniform degradation over time. This maintains image uniformity at the time of manufacture but also as the panel ages. This system was licensed to LG Display in 2021 and is currently used in active-matrix OLED TVs sold worldwide.

Although faculty and students investigate and participate in multiple areas of research related to display technologies, there is no single specialized program or study area dedicated to display sciences. Aspects of display technology are researched across multiple institutes. For example, liquid crystal research is covered in the Institute of Physical Chemistry (led by Frank Giesselmann); organic semiconductors are investigated in the Institute for Polymer Chemistry (Sabine Ludwigs); and optical system research is covered in the Institute of Applied Optics (Stephan Reichelt). IGM's current focus is on researching manufacturing processes for displays (specifically backplane-related processes), as well as backplane design, novel pixel circuit concepts, and overall display-driving and integration. IGM is part of the Stuttgart Center of Photonic Engineering (SCoPE) and Center for Integrated Quantum Science and Technology (IQST). These centers integrate study and research from myriad disciplines, within multiple institutes at the university.

When asked what brought Fruehauf back to academia after working in the private sector, he said, “Around the time of my return, it was still common that German universities recruited professors in engineering from the community of scientists with industry backgrounds who had been leading industrial research or development teams or larger groups, preferably combined with experience gained in a foreign country. The offer of the directorship of the Chair of Display Technology, which in 2011 was renamed IGM, was a very unique opportunity for extremely independent scientific work in the area of display manufacturing processes and display systems. Another important reason was the opportunity to teach, which I had enjoyed immensely while working on my own advanced degree,” he said.

IGM follows the typical structure of German engineering institutes. Besides the institute director and several senior scientists (two in IGM's case), who are responsible for the acquisition, administration, and scientific oversight of the various third party–funded projects, PhD candidates perform the research work. These are fully paid positions that involve working on specific research projects (the candidates are no longer considered students, as they typically have no requirements to fulfill). However, they have teaching obligations and a relatively high self-reliance and responsibility for all aspects of their specific research projects.

The PhD candidates also handle the daily supervision of various bachelor's and master's students’ research projects. These are typically projects and topics that are closely related to or emanate from the PhD candidate's own research project. Examples include developing a display driver's electronic system or investigating process as alternatives for the overall system that is developed by the PhD candidate.

In addition to the AMOLED feedback circuit with external compensation, Fruehauf and the IGM research team have pioneered additional display advancements (Fig. 3). These include a cost-efficient (only 5 lithography masks) low-temperature polycrystalline silicon (LTPS) process and a metal-oxide TFT process that uses specific oxygen diffusion barrier layers to improve the stability of indium gallium zinc oxide (IGZO) transistors. These have not yet been applied in mass fabrication.

“We also developed a high-temperature and high-brightness-resistant AMLCD for integration into automotive headlights, for which we were awarded the SID I-Zone award in 2017,” said Fruehauf. “These displays had been integrated into Porsche test cars to demonstrate the benefits of highly adaptive headlights. Another recent development has been the realization of an active-matrix liquid crystal-based reflective intelligent surface (RIS) for radio beam forming in future 6G mobile phone systems.”

In the display field, Fruehauf sees the potential for simplifying TFT manufacturing processes as well as improving microLED contact methods, which also could be useful for repairing these precision displays.

Fruehauf sees many opportunities for advancement outside of traditional display technologies. In addition to the RIS system (Fig. 4), the group is investigating and developing innovative packaging technologies using the facility's ultra-high precision printer for contacting chiplets and wide bandwidth contacts to high-frequency microchips as well as innovative quantum sensing systems (e.g., for nitric oxide detection in the breath of humans and animals). These sensing systems present a non-invasive way to help diagnose and manage respiratory diseases such as asthma.

As with many US universities, the University of Stuttgart has faced—and continues to face—challenges in securing adequate funding. Maintaining a large clean room can be an expensive proposition. According to Fruehauf, fundraising requires significant effort to acquire outside research grants from the European Union (EU), federal and state governments, as well as direct research grants from private industry. Over the years, most of IGM's funding has come from outside third-party sources—roughly half from public research grants and the other half from direct bilateral research partnerships with private companies.

This has required Fruehauf and his colleagues to strike a balance between basic theoretical research projects—funded primarily by government grants—and more practical application-related research, in which private companies invest. The benefit of the broader research projects is that these often lead to innovative new technologies that are essential to the institute for acquiring future industry grants.

Another challenge has been continuing to attract talented new engineering students to the university. While areas such as artificial intelligence (AI) and mechanical and computer engineering continue to attract new students worldwide, other areas of engineering have waned in popularity, particularly when offered only in a local language (in this case, German). Fruehauf said the University of Stuttgart has been able to counter this development by installing two new English-language master's programs: Infotech (a crossover of electrical engineering—specifically communication technologies—and computer science) and a master's of science in electrical engineering, which is an identical English copy of the school's corresponding German language electrical engineering program. These offerings have allowed the university to tap into a huge pool of international students.

By eliminating the language barrier and offering this education at a competitive cost, enrollment has stayed high. It is important to note that there is no tuition fee for German and EU citizens and only a moderate tuition fee (∼€1,500) for non-EU citizens who enroll.

Like most German universities, the University of Stuttgart is considered a state university. As such, the university provides basic funding for IGM—a salary for Fruehauf and four staff, facility costs (e.g., building maintenance and energy expenses), and a small discretionary budget. The brunt of funding must be acquired by the institute itself. The responsibility for this acquisition falls upon the director (Fruehauf) and his senior scientists. The university provides legal support for formulating the research contracts and filing for patents.

According to Fruehauf, the secret to IGM's success stems from finding a cost-effective organizational structure for maintaining critical facilities like the clean room. This, together with a highly competent and highly motivated team, has been instrumental to the long-term survival of the entire facility and, by extension, for continued success in research and development.

Fruehauf said that IGM's available equipment and infrastructure is outstanding, particularly by academic standards, and this has allowed the institute to work on unique scientific challenges that are too complex for most competing university laboratories. IGM can design and fabricate entire active-matrix displays with hundreds of thousands or even millions of pixels. This is well beyond the capabilities of most university laboratories, with most only able to manufacture single TFTs. Yet it still pales in comparison to the capabilities of the industrial research and development facilities of large private corporations, which typically have a shorter time to market than university research projects.

At a broader level, the University of Stuttgart places a high emphasis on interdisciplinary research. They call it the “Stuttgarter Weg” (“Stuttgart Way”). An example is the close cooperation between engineering and physics departments (and other basic sciences) in the IQST Center, where the team works on bringing new quantum-based sensor concepts from basic science to applications. “We are effectively bridging the valley of death between basic science and industry,” said Fruehauf.

Fruehauf feels that microLED display technology could have a profound impact on the entire display industry, but only if the transfer problem can be solved, and that is no small challenge. MicroLED's current low yield rates and high manufacturing costs place it outside the budgets of most TV and display buyers. “A success in this area could eliminate the cost benefit of extremely large substrate sizes in the manufacturing line (e.g., high generation substrates), potentially even enabling the re-establishment of display production in Europe and the United States.”

Fruehauf also sees promise in the continuous improvement of TFT backplane resolution to enable the extremely small (ideally submicrometer) pixel sizes of future holographic displays.

Various factors contribute to increasing the employability of IGM students after graduation or completion of their degrees, including professors who have spent part of their career in private industry, a curriculum with various lab projects, and the requirement to complete three research projects to earn a master's degree. “It is common that the students are co-authors on the papers of their supervising PhD candidates, although it is more seldom that the outcome of solely a bachelor's degree or master's thesis is significant enough to allow a student to be the main author on a research project,” said Fruehauf.

In Germany, engineering graduates with bachelor's or master's degrees typically pursue a career in research and development at private companies. In contrast, graduates of applied science programs typically pursue careers in maintenance, sales, and manufacturing lines.

According to Fruehauf, only about 15 to 20 percent of students go on to pursue a PhD. With their more extensive knowledge and experience, these PhD graduates are frequently hired as group leaders or divisional managers in tech companies, but a few choose to stay in academia.

“Only a very small percentage of our graduates pursue academic roles such as junior professorships,” he said. “Our graduates are in a very fortunate situation, in that the Stuttgart area is one of the most prominent high-tech areas in Germany and in Europe at large.”

Stuttgart is currently in the top five ranking cities for patents per inhabitant, with esteemed multinational firms such as Mercedes, Porsche, and Bosch headquartered there. It is also home to the German divisions of many global tech companies, including IBM, Hewlett-Packard, Nokia, Bell Labs, and Sony. This gives IGM graduates many opportunities to enter private industry and apply the skills and knowledge learned at the institute.

In his professional life, Fruehauf's proudest achievement (so far) is the invention of the hybrid OLED pixel compensation principle now used in AMOLED TVs. On the personal side, Fruehauf expressed great pride in his family: his wife teaches ballet, and his son is a student pursuing a master's degree in science.

When he is not busy in the laboratory, clean room, or lecture hall or speaking and attending industry conferences, Fruehauf finds great satisfaction in two things: swimming and world history. “Since my teenage years, I have been an active swimmer (although the time of swimming in competitions has long passed). Additionally, I am extremely interested in history, elaborately consuming various forms of documentaries and historical content in both book and video formats.”

With geopolitical issues causing some turmoil in the display market, as well as in the tech industry at large, IGM faces the challenge of staying relevant. Display technology is primarily industry-led, which makes it difficult for universities and other research institutions to have a direct impact on the display technology evolution. Historically, the display industry has relied on investing heavily into new, larger, more efficient manufacturing lines to realize economies of scale rather than revolutionary technological improvements.

But with this maturation of the display industry and laser focus on costs, IGM can add some value. “The current maturing of established display technologies opens up new opportunities for research institutions, as it increases the demand for entirely new and more cost-efficient approaches that had long been overlooked, because the necessary cost reductions could be achieved by mere evolutionary approaches (e.g., investing in a newer generation fab),” said Fruehauf.

With his retirement approaching in 2028, Fruehauf sees excellent opportunities for the university and for his successor at IGM. “The future holds many exciting opportunities, including the further development of large-area microelectronics such as hybrid integration for chiplets and a multitude of innovative applications of the available large-area technologies for display and sensor array applications. These opportunities, enhanced by the ‘Stuttgarter Weg,’ should allow IGM and the university to effectively apply our technological expertise in important new areas and ensure the university's relevance into the next decade and beyond.”