Designing and fabricating custom semiconductor devices for next generation research.
MIT is filled with numerous "labs," but when it comes to fabricating and testing semiconductor devices, the institute has combined its eggs into one very high-tech basket known as Microsystems Technology Laboratories (MTL). Founded in 1984, MTL differs from most university laboratories in that its mission is to serve the entire university rather than just a single research group.
"Typically at a university, every faculty member has a private lab," says Dr. Vicky Diadiuk, MTL's Associate Director, Operations. "But MTL is different in that we're a shared facility."
Principal Research Engineer
Associate Director, Operations
MIT Microsystems Technology LaboratoriesMost of the students who use the facilities are from MIT's Schools of Engineering and Science, but users have come from 29 departments, labs and centers, says Diadiuk. In addition to providing economy of scale in facilities costs, MTL provides 15 full-time staff members who maintain tools, train students, and generate basic processes. This provides a strong competitive advantage for recruiting faculty, who may not want to spend their first few years setting up a facilities-intensive lab, says Diadiuk.
"Everything is already set up when they come in, including the professional staff, machines, basic processes, and sometimes even the specific recipes they need," she says. "Most faculty would rather spend their time doing research."
Diadiuk should know. She spent many years doing optoelectronic device research at MIT Lincoln Laboratory prior to starting at MTL in 1996. As Associate Director, she oversees MTL's daily operations, reporting to MTL Director and Electrical Engineering professor Vladimir Bulovic.
MTL consists of three cleanroom laboratories, offering different levels of cleanliness and sophistication. The crown jewel is the second-floor lab, which provides "what you would find in a commercial fab, except for the vastly different scale," says Diadiuk. On the fourth floor, the Technology Research Lab offers fewer restrictions and more flexibility. "Some of our innovations in processing and materials start there, and if they're compatible with mainstream fabrication, they can come down to the second floor," says Diadiuk.
The fifth floor lab is "kind of a garage works, where anything goes as long as it's safe," says Diadiuk. "There's no barrier to entry or contamination concerns, so people can play there and develop processes. When they discover that cleanliness matters, which is a more natural way of learning than being told, some of them migrate to the cleaner labs downstairs."
Moving Beyond Silicon
As with the semiconductor industry at large, MTL typically depends on silicon as the substrate material. Yet, the lab is increasingly using light-emitting and -responding materials like III-V compounds, says Diadiuk. Gallium nitride is a "very exciting material right now," says Diadiuk. "The wafers are very expensive, but they can be used on the same equipment we use for fabricating devices on silicon and the other III-V semiconductor substrates like indium phosphide and gallium arsenide."
Because MTL generates a wide variety of devices for experimental purposes, researchers seldom use a full 25-wafer lot, even though the tools can handle them. "We use six-inch diameter or smaller wafers whereas modern industrial tools are set up for eight or 12 inches," says Diadiuk. "For this and other reasons, like the availability of replacement parts, we must constantly renew our toolset."
Last year the lab acquired a "really cool state-of-the-art e-beam writer," says Diadiuk. This direct-write lithography machine does not require a mask, and supports features as small as a few nanometers.
In recent years, MTL has increasingly applied semiconductor fabrication technologies to the manufacture of a variety of tiny devices. "We use the same processes used to make transistors to make things like micro-reactors and DNA chips," says Diadiuk. MTL is also "pushing the envelope with other materials like plastics and polymers."
The range of devices built at MTL is impressive. In the first three months of 2013 alone, MTL announced participation in projects including nanowire-based solar cells, optical phased arrays for medical-imaging, and a super-fast new p-type transistor. MTL also houses four special research centers, focusing on integrated circuits (CICS), medical devices (MEDRC), graphene devices (MIT-CG) and gallium nitride (MIT-GaN), respectively.
One of the most ambitious projects MTL ever undertook was a MEMS micro-engine project led by MIT's Martin Schmidt. "We had about 42 researchers and many more students working on it, and we used essentially every technology we know," recalls Diadiuk. "The project led us to think about designing semiconductor devices in three dimensions. We aligned and bonded up to seven wafers, which was fairly heroic, and fabricated a turbine the size of a shirt button. The experience made us really good at wafer bonding and deep etching."
Having a single shared facility for fabrication not only reduces costs and improves recruiting, but it also pays off with greater safety. "We often use dangerous chemicals and gases that can explode and burn and do all sorts of bad things," says Diadiuk. "You really don't want to have 22 different labs, each one with its own cylinder of toxic gases."
Diadiuk is proud of MTL's safety record, which she says has been kept up with the assistance of MIT's Environmental Health and Safety (EH&S) office, as well as MIT Facilities, which maintains the detection systems. Among other precautions, the facility has toxic gas detectors on every floor and near every tool that uses them, supported with redundant systems. Hydrogen is kept in an explosion-proof bunker, and there are numerous hydrogen detectors.
Perhaps the most important safety measure is training. This is a challenge, says Diadiuk, considering that about 500 students per year use the lab. All users must have hands-on experience in microfabrication or take a regular semester-long course, Introduction to Microfabrication (6.152); if curricular credit is not desired, users can instead opt for an intensive one-week lab-only version. Before entering the lab, students, faculty, and other users are trained on lab-specific EH&S requirements. Once inside, they are taught how to use specific machines.
Researchers from other universities are also welcome to apply for lab access, as long as they go through the same training regimen. Most visitors are from Boston-area schools, says Diadiuk, but some have come from other parts of the country and overseas as well.
Open to Industry, from Start-ups to MIG
Industry can gain access to MTL's labs via the Fabrication Facilities Access (FFA) program. Since larger companies tend to have their own facilities, the labs are primarily attractive to start-ups, says Diadiuk. "Companies can send engineers to use our cleanroom as long as their processes don't pose a risk of cross-contamination, and they pass all safety exams. There's very little IP entanglement, which the start-ups really like."
Sometimes larger manufacturers use the facilities for special projects they can't develop with their own pilot lines. Here, MTL's expertise in non-traditional fabrication is particularly attractive. "Making a material change for them is really hard, but for us, it's pretty straightforward," says Diadiuk.
Some companies are members of a sponsor group called the Microsystems Industrial Group (MIG), which advises and helps fund the lab. Sometimes MIG members direct part of their contributions to particular research programs. "It's a highly interactive participation," says Diadiuk.
A number of MIG members donate equipment to help keep the lab up to date. Although it's usually "at least one generation behind," according to Diadiuk, it's still close enough so that "by the time our students graduate they are often fully trained on essentially the same equipment they would use in the workplace."
MIG's financial contributions, meanwhile, help offset general infrastructure costs, which are typically beyond the charter of research grants. Despite this funding, plus several million dollars a year from MIT, MTL continues to seek new ways to stay competitive. In fact, MIT is now in the planning stages to build a brand new MTL facility.
In this and other projects, MIG members provide valuable feedback and direction, and both sides keep each other up to date on the latest developments, says Diadiuk. "Our interactions with industry provide a sanity check," she says. "They bring us back to reality."
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