Section 4

MEMS/Microsystems Infrastructure

4.1 Organizational Infrastructure

The organizational infrastructure for support of research and commercialization efforts in MEMS and microsystems in Europe is substantial and well evolved. Research funding programs at the European and national level were described in Section 3 of this report. The first sub-section of this section will give an overview of the kinds of facilities in place and activities under way in European universities, research institutes, national laboratories, start-up companies, and fabrication services. The second sub-section of Section 4 covers the technical infrastructure for MEMS/MST, in such areas as design and modeling; processing technology; packaging technology; and testing and reliability.

The intent of the section is not to provide a comprehensive review, but to present a representative sample of the evolving European infrastructure in these areas, based on the experiences of our strategic technology tour team in Europe.

Universities

When the MCC team planned the itinerary for the Strategic Technology Tour in MEMS and Microsystems, we decided to favor site visits to industry players over those to universities. As it turned out, the university visits were extremely valuable and informative, both from the standpoint of the research underway at the universities and from the perspective that these visits gave our group on activity in European industry.

Among the primary observations of the MCC team on activity at European universities were:

EPFL, in Lausanne, Switzerland, provides a good concrete example of several of these trends at an institution with a very strong research program in MEMS and microsystems, and we will describe EPFL here. Other universities among the leaders in Europe in the field are the University of Delft, the Catholic University of Leuven, the University of Twente, the University of Grenoble, and the University of Karlsruhe.

EPFL (The Swiss Federal Institute of Technology)

EPFL (The Swiss Federal Institute of Technology) research concentrates on four areas: MEMS/MST devices, systems integration efforts designed to incorporate MST devices into systems, microfabrication technologies, and approaches to the management of technology. The clear emphasis is on the practical application of MST technologies, rather than on theoretical work, with many examples of cooperative work and contract research with European companies. Several spin-offs have emerged from EPFL for commercialization purposes. EPFL cooperates closely with IMT (the University of Neuchâtel) and CSEM.

The microsystems work at EPFL takes place within the Institute of Microsystems, a multi-disciplinary institute which currently operates four primary research groups:

Further detail on the content of the research programs of EPFL’s Institute of Microsystems is available from the Institute’s Web site at http://dmtwww.epfl.ch/ims/.

EPFL has an impressive physical facility on what must be one of the most beautiful campuses in the world, overlooking Lake Lausanne and the Swiss Alps. The Institute of Microsystems has in-house fabrication facilities for microsystems, which are being upgraded in 1999 with the addition of a new 10,000 square foot clean room. Among the more unusual pieces of equipment at EPFL is a micro-stereolithography station that supports the fabrication of complex three-dimensional shapes. The process involves the projection of an “active mask” using a laser which induces a space-resolved photopolymerization of a liquid resin. The superimposition of a large number of layers (up to 1000 or more) results in the manufacturing of real three-dimensional objects. Curved and conical surfaces can be obtained as well as hollow volumes.

Much of the research work in microsystems at EPFL is closely linked to the requirements of European industry. In particular, the graduate student projects described to our MCC group during the visit to EPFL were almost all being conducted in direct collaboration with industry partners, with industry providing funding support in most cases. Among the industry sponsors of work within the Microsystems Design Group, for example, are Siemens, as well as four Swiss firms — Baumer Electric, Metrolab, RMB ST, and Sentron.

EPFL’s spin-offs have been created as commercialization mechanisms for technology developed at the university. Two of these were described to our group:

In addition to its role in microsystems-related research, EPFL serves an important role by educating young researchers who move to industry. Currently, approximately 400 students are studying microsystems and micro-engineering throughout the Institute of Microsystems, with 80-100 working toward PhDs. EPFL produces approximately 25 PhDs per year in microsystems, with most of these graduates then taking industry positions. The student body and faculty of EPFL are international in make-up: one-third of undergraduates, one-half of PhD students, and one-half of the faculty are non-Swiss.

Research Institutes

Research institutes of various descriptions play an important role in the MEMS and microsystems domain throughout Western Europe. Most of these institutions receive funding from national governments as well as from industry contracts, many also compete for contracts through EC-funded programs, and many are positioned within leading universities. Among the roles played by the research institutes are: (1) the creation of multi-disciplinary centers of excellence in microsystems research which function to pull together faculty and research groups from different parts of a university or universities; (2) the conduct of “pre-competitive” (but usually industrially relevant) R&D that addresses emerging industry requirements; and (3) the undertaking of early-phase development work necessary to establish the commercial viability of promising university research.

The European research institutes the MCC Strategic Technology Tour team visited were the Fraunhofer Institute (Germany), TIMA (Techniques of Informatics and Microelectronics for Computer Architecture - France), IMEC (Belgium), and the Mesa Research Institute (the Netherlands). Brief descriptions of these organizations are provided in this section; for additional detail on the primary areas of focus of their technical work, consult Chapter 5 of this report.

The Fraunhofer Institutes

Founded after World War II, the Fraunhofer Institutes are a decentralized research organization which was given the mission of conducting R&D that would help Germany rebuild its industrial strength. The scale of the Fraunhofer is huge: 5400 full-time researchers, 3400 part-time researchers and graduate students, 50 separate locations throughout Germany, six “outposts” in the United States. Three of the Fraunhofer branches which have R&D activities in the microsystems domain - Dresden, Munich, and Duisberg - have grouped themselves into a cluster called the Fraunhofer Institute for Microelectronic Circuits and Systems (the Fraunhofer IMS). Among these three the total number of researchers working in MST is approximately 425. The Fraunhofer IMS also cooperates frequently with the Technical University of Munich.

As an example of microsystems work within the Fraunhofer IMS, the Fraunhofer Munich branch is doing R&D in two primary areas:

By contrast with the research program at Munich, where the emphasis on microfluidics is strong, Duesburg concentrates on CMOS-based processes, and Dresden on the integration of other materials with CMOS.

The Fraunhofer branch in Munich has over 200 square meters of clean room space dedicated to MEMS. The laboratory infrastructure includes the following elements:

Funding for the Fraunhofer comes from a mixture of sources, with approximately the following proportions: 25 percent from the Fraunhofer Society (endowment); 45 percent from industrial contracts; and 30 percent from public R&D funding programs.

TIMA

TIMA (Techniques of Informatics and Microelectronics for Computer Architecture), an academic institute located in Grenoble, France, is a “Research and Service” unit of CNRS (the French National Scientific Research Center). The laboratory is also linked organizationally to the National Polytechnical Institute of Grenoble (INPG) and Joseph Fourier University (UJF). TIMA has an overall research staff of approximately 100, including graduate students, divided into six major research groups. These groups are:

Most of the research at TIMA in MEMS and microsystems takes place in the Microsystems Group, headed by Dr. Bernard Courtois. Related work, however, is also under way in the Qualification Group (for example, testing of devices for behavior in harsh environments) and the System Level Synthesis Group (design software and multi-domain simulation).

Research at TIMA in the microsystems domain began with the establishment of the Microsystems Group in 1994. The original director of the group was Jean-Michel Karam, who has since left to direct a start-up company called MEMSCAP. Currently, the Microsystems Group has research work in progress in the following areas:

Two private spin-off companies have emerged from the research program in MEMS and microsystems at TIMA: MEMSCAP, which specializes in design tools for MEMS devices, and AREXSYS, in hardware/software codesign.

IMEC

IMEC (Interuniversity Microelectronics Center), located in Leuven, Belgium, was founded in 1984 by the Flemish government to create a center of excellence in microelectronics research and development. With an annual budget of approximately $80 million, IMEC has a staff of over 800 if visiting scientists and graduate students are included. Some 100 students at the Masters and PhD levels do research at IMEC; 120 PhD candidates have prepared their dissertations at IMEC. IMEC is located on the campus of the Catholic University of Leuven, and also has formal relationships with the University of Gent, the Brussels Free University, Limburg University, and the University of Antwerp.

IMEC’s funding break-down is approximately 40 percent government support from the Flemish government (in Belgium) and 60 percent contract research. Contracts include research work from the EC, as well as private industry. (IMEC receives some of its private-sector funding from organizations outside Europe.) IMEC both trains researchers who will later work in industry positions, and develops technology that can be transferred for commercialization either to its industry partners or to spin-off companies. The start-up Co-Ware, a provider of hardware/software codesign tools, is one of 14 IMEC spin-offs. In its contract work with industrial partners, IMEC seeks to retain intellectual property rights to underlying enabling technology, while licensing the necessary applications of this base technology to the partner.

IMEC’s research program concentrates on the development of process technologies for fabrication of future generations of integrated circuits, optoelectronic components, microsystems, sensors, and solar cells. There is a strong emphasis on CMOS, with work in progress on 2.5 V and 1.2 V technologies at 0.25 microns; a 0.18 micron CMOS process which has involved work on a shallow trench isolation module, the scaling down of LOCOS-based processes, thin gate dielectrics, and advanced silicidation techniques; and a 0.35 micron mixed analog/digital CMOS process for automotive and telecommunications applications. Laboratory facilities at IMEC are considerable: They include a 1,750 square meter pilot line for 150 mm wafers, half of which operates at Class 1; pilot lines for multi-chip modules (MCM), MMIC-HEMT, and solar cells; a packaging and test laboratory; a facility for automated device and circuit testing; a physico-chemical analysis laboratory; and a well-equipped microsystems laboratory.

The MESA Research Institute

The MESA Research Institute (MRI) is located with the University of Twente, in the Netherlands, both physically and organizationally. The acronym MESA has an interesting origin: M comes from microelectronics, E from materials engineering, including molecular engineering, while SA stands for sensors and actuators. MRI thus brings together researchers from four departments within the University of Twente — Electrical Engineering, Applied Physics, Applied Chemistry, and Mechanics — to focus their research efforts in the MST domain on micro-electronics, materials, molecular engineering, and sensors and actuators. MRI does work at both the device and system level.

The size of the research staff at MRI is approximately 80, with total staff size about 140. The annual budget is approximately $10 million. The research program at MRI is organized into nine divisions, each focusing on a particular research theme. The divisions are as follows:

In each of these divisions, 10-12 individual research projects are in progress (some of which represent PhD dissertation projects).

Twente Micro Products (TMP) is a spin-off of MRI aimed at small/medium scale production of microstructure devices. The company was spun off from MESA in 1995 in order to bridge the gap between academic research and industry.

Fabrication Services

Europe has moved aggressively to create mechanisms to provide access to fabrication capabilities for MEMS and microsystems for companies and institutions which want to attempt integrated MEMS/MST devices and components into their systems.

Europractice Manufacturing Clusters

The five microsystems manufacturing clusters for MST function within the Europractice program to provide access to fabrication capabilities for the MEMS/MST user community. The five clusters have both a regional and a technological focus, as follows:

Customers who require design services and process consulting, in addition to access to fabrication capabilities, can make use of a parallel set of clusters called the “Competence Centers.”

More detail on the Manufacturing Clusters and the Competence Centers, as well as on the Europractice Program in general, is found in Section 3 of this report.

Multiclient Fabrication Services — CMP

The Circuits Multi-Projets (CMP — or, in English, Multi-Project Circuits), located in Grenoble, France, was established in 1981 for the fabrication of integrated circuits. Like MOSIS in the United States, the objective was to give research groups in both academia and industry access to IC fabrication capabilities for the prototyping and low-volume production of semiconductor devices. This was achieved by negotiating with semiconductor fabs on behalf of a class of users, rather than individuals, in order to achieve reasonable scale, and by grouping together the IC designs of multiple users on the same semiconductor wafer. CMP is managed by the research institute TIMA (Techniques of Informatics and Microelectronics for Computer Architecture).

CMP now handles orders for multichip modules (MCMs) and MEMS, as well as conventional integrated circuits. In the MEMS domain, CMP provides access to fabrication capabilities at Austria Mikro Systems (AMS), Philips, CSEM in Switzerland, and MCNC in the United States. The particular fabrication technologies available through CMP are:

CMP makes available design kits based on Cadence and MEMSCAP software, which aid users in creating device designs for the fabrication processes at AMS, Philips, and MCNC (now the spin-off CRONOS). CMP reports that it has handled 2700 fabrication projects requiring a total of 280 production runs, with devices purchased by 200 universities and research institutes as well as 70 private sector firms.

In addition to these process-specific design kits, CMP provides a more generic MEMS engineering kit called VULCAIN. Developed by the Grenoble-based design software house MEMSCAP, VULCAIN runs in conjunction with Mentor Graphics to provide a suite of design, layout, and verification tools. Among these are:

[Source: Feature set from CMP/MEMSCAP literature]

For additional details on CMP, see http://tima-cmp.imag.fr/CMP/CMP.html.

Start-up Businesses

Commercialization activity around MEMS and MST has spawned a level of start-up and entrepreneurial activity that is still uncommon in Europe in other technology domains. These start-ups can be classified in two primary categories:

Among the technology developers are such firms as MEMSCAP, which has readied a commercial version of MEMS design software based on work performed initially at TIMA. As noted above, Mimotec, a spin-off of EPFL in Switzerland, makes molds for the fabrication of microsystem components. Design and fabrication service providers are represented by such examples as Twente Microproducts (TMP). TMP emerged from the MESA Research Institute, and provides design and fabrication services that leverage the research capabilities of MRI together with fabrication facilities at Onstream B. V. (previously, a division of Philips.) TMP offers OEM customers what they call a “seamless microsystem engineering” (SME) process, which means they will handle the technical project management and coordination from the first idea to final MST production. Tronics, based in Grenoble, France, seeks to manufacture and commercialize MEMS products developed at LETI,, a major nationally funded French research institute.

Professional Societies and Not-for-Profits

VDI/VDE-IT is probably the most important organization in this category in Europe for the MEMS and microsystems field. VDI/VDE is a major German professional society for engineers — somewhat similar to the IEEE. VDI/VDE Technologiezentrum Informationstechnik (VDI/VDE-IT), a private not-for-profit organization, emerged from the society and concentrates its efforts on the microsystems field. Perhaps its most visible activity outside Europe is publication of the MST News, a very useful newsletter describing developments in MEMS and microsystems in Europe. In addition to print distribution, MST News is available electronically at http://www.vdivde-it.de/mst. In addition to this publication, VDI/VDE-IT provides a set of services to small and medium-sized firms operating in the MST arena, in the following areas: the analysis of technology trends, the conduct of technology studies, consultation with client companies in the introduction of new technologies and on innovation management, the provision of assistance in establishing new start-up companies, and the facilitation of efforts to find appropriate partners for research projects.

The Virtual Corporation in MST

It was a general observation of the MCC Strategic Technology Tour team that the different elements of the “organizational infrastructure” for MEMS and microsystems in Europe—including the universities, research institutes, national laboratories, industry associations, start-ups, and established firms—demonstrate a high level of interaction and inter-communication. For example, the universities we visited are well linked to industry, and many graduate students are working on projects in close collaboration with industrial partners. The start-ups, in many cases, work to coordinate access for interested users and system designers to the fabrication capabilities of large industrial players or national labs, and also provide customized design services. Everyone seems to participate in NEXUS, to one degree or another.

Our observation was that these interactions, in many cases, represent more than the ad hoc communications of a technical community with shared interests. Along some dimensions, a “virtual corporation” is emerging in Europe in the microsystems domain, with different institutions specializing in specific aspects of the overall technology value chain, and then building systematic relationships with other organizations with complementary strengths. One member of our team, Eric Leonard of Eastman Kodak, used an enterprise modeling approach to analyze this phenomenon.

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4.2 Technical Infrastructure

One of the STT team’s objectives was to investigate the technical infrastructure consisting of such crucial areas as design and modeling tools, processing and packaging, and testing and reliability for MEMS and MST. During our site visits we gathered information on these topics. The data provided by our hosts was relatively scant, indicating an “ad-hoc” approach to most of these areas, but sufficient to support several high-level observations

Design and Modeling

In the area of design software, the R&D groups we visited tended to do their design work on general platforms such as Cadence and MentorGraphics, Also, almost every research group our team visited uses ANSYS for finite element modeling and the simulation of MEMS/MST devices. Some of the groups are starting to explore MEMS-specific software packages such as MEMCAD™ by Microcosm and MEMSCAP™ by MEMSCAP. In particular, MEMSCAP is a French company; the software by the same name was originally developed at TIMA (University of Grenoble) before spinning off as a start-up company.

MEMS/MST Processing Technologies

In the area of MEMS/MST fabrication the host institutions displayed a wide variety and depth of processing capabilities.

Such start-up businesses as Twente Microproducts and Tronics are also specializing in coordinating design and fabrication services for technology users who wish to prototype MEMS devices or microsystems for exploratory use in their applications.

The area of high aspect ratio structures appears to be of particular interest to many research groups with applications both in the fluidic area as well as in micromolding of miniature 3D parts. The STT team encountered multiple process development efforts directed at this area. Here follows a brief description of some of these novel efforts.

Microstereolithography (EPFL)

Microstereolithography is a 3D microfabrication process which allows one to prototype complex 3D objects which cannot be built by traditional microfabrication processes.

EPFL has developed a high resolution stereolithography machine (Fig. 4.2). In this process, the objects are fabricated layer by layer. A dynamic pattern generator along the optical path shapes the light beam to produce the layer-by-layer images. The images are projected onto a thin layer of photopolymer to produce a “slice” of the desired object. The object is then lowered slightly into the photopolymer which spreads onto the object surface. Then the next layer is exposed. A large number of layers (up to 1000 or more) have been used to produce 3D objects. Curved and conical surfaces can be obtained as well as hollow volumes.

Given the sequential nature of this process, it might not lend itself to the manufacturing of any significant quantity of devices. However, it appears to hold the potential to be a powerful tool for rapid prototyping of microstructures. It can also be combined with LIGA-type processes to produce non-vertical structures.


Fig. 4.1. Examples of 3D shapes fabricated with micro-stereolithography.

MIMOTEC (EPFL)

As an alternative to LIGA for high aspect ratio microsystems, EPFL is conducting process development work based on SU-8, an epoxy based, chemically amplified photoresist system with excellent sensitivity and high aspect ratios. A broad range of thicknesses can be obtained in one spin: from 750 nm to 200 µm with a conventional spin coater. Ultra-thick layers of 450 µm have been obtained with a spin coater equipped with a rotating cover. The resist is exposed with a standard UV aligner and has an outstanding aspect ratio of up to 15.

This technique can be used for microfluidics (e.g. microchannel fabrication). Also, combined with the electroplating of copper it allows the fabrication of highly integrated electromagnetic coils. In addition it can be used to fabricate molds for the low cost volume production of polymer microdevices. A process called MIMOTEC (MIcroMOlds TEChnology) has been developed for the fabrication of metallic micromolds. MIMOTEC is based on the use of the SU-8 in combination with electrodeposited nickel.

These molds have already been used in volume production of thermoplastic microcomponents (micro-gear) for low cost watches.


Fig. 4.2. Schematic picture of EPFL microstereolithography machine.

DEEMO (MESA)

DEEMO (Dry Etching, Electroplating, Molding) is a project at the MESA Research Institute with the objective of developing a fast and flexible production process for polymer microstructure products, while featuring low initial cost and a fast prototyping cycle.

DEEMO is a process in which the expensive X-ray lithography step of the LIGA process is substituted by a dry etch process in silicon. The DEEMO project has produced metal mold inserts by electroplating on dry etched structures. Resolution to date ranges from a few microns to tens of microns. The project is being funded by the EC ESPRIT Program.

Sub-Micron Machined Trenches (Philips)

Even though not strictly MEMS or microsystems work, Philips presented this process technology as an example of micro-machining capabilities at the Philips Research Laboratories.

Philips has developed a photo-electro-chemical etching process to form arrays of ultradeep micron-sized trenches. To this effect it uses an HF solution on lightly n-doped silicon in combination with an applied potential and light. Typical geometries are hole or trench diameters of 1 micron and depths exceeding 100 microns. After forming the holes, the trench walls are made highly conductive by phosphor diffusion into the silicon from a deposited phosphorous silicate glass (PSG) layer. Next the trenches are filled with 30 nm of ONO dielectric consisting of a thermal oxide, LPCVD-deposited nitride and anoxide layer made from LPCVD-TEOS. As a final step this dielectric layer is covered by n-type polysilicon.

This process yields an on-chip capacitor with a hundred-fold increase in active surface area when compared to planar approaches. This technique might find a use in other microsystems applications.


Fig. 4.3. Molded polymer gears for low cost watch product (MIMOTEC).


Fig. 4.4. SEM photograph of Si micromolds fabricated at MESA using Si dry etching.

MEMS/MST Packaging Technologies

In the area of MEMS and MST packaging, much of the work for microsystems in progress at individual European firms is reported to be based on company- and application-specific approaches, and is often treated as proprietary and as a potential source of competitive advantage in the marketplace. University groups typically had non-existent or smaller efforts in this area. Lack of standard, open packaging may, however, retard the commercial acceptance of MEMS and MST by the user community in Europe.


Fig. 4.5. High-value capacitors made in ultra-deep trenches in silicon (Source: Philips)
(a) SEM micrograph of hole array

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(b) Micrograph of hole cross-section illustrating fabrication.

Packaging at LETI

The most impressive work described to our team was found at CEA-LETI in France. LETI has applied its decade-old expertise in microelectronics and multi-chip module packaging to MEMS and microsystems. The technology developments include a hybrid flip-chip approach where the MEMS device is attached to the integrated A/D and control circuitry via solder balls. The solder balls end up with a diameter of approximately 60 microns and a 40 micron height. The flux-less re-flow process includes the application of a pre-formed solder ring around the edge of the MEMS chip in order to provide a hermetic seal and controlled atmosphere for the MEMS device.

Another novel approach developed at LETI and subsequently transferred to the start-up TRONIC uses wafer-level processes to yield an SMT-ready chip-scale package.

The MEMS device is fabricated on a (silicon-on-insulator) wafer substrate. A silicon cap wafer is also micromachined through anisotropic etching in such a fashion that tapered vias are opened over the MEMS I/O pads. Next, the MEMS I/O pads are gold wirebonded to the top of the package lid. Then the via holes are filled with an epoxy resin. After cure, the resin and wirebond ends are polished off to yield a planar package top and metallization applied to form the package I/O pads.


Fig. 4.6. (a) LETI flip-chip packaging of MEMS accelerometers


(b) LETI chip-scale package for MEMS accelerometers

In-Process Packaging (Siemens)

Siemens, in keeping with its approach of developing MEMS devices that can be fabricated on its standard BiCMOS process line, has developed an in-process encapsulation process. This process encapsulates the MEMS devices using a final structural poly-silicon membrane layer. The devices (pressure sensors and accelerometers) are released after deposition of this capping layer by etching out a silicon oxide layer through etch holes in the membrane. The etch holes are then plugged using a proprietary process.

Both the Siemens and the LETI approach have significant potential for low-cost packaging. They are both wafer-level approaches, enabling batch processing for high volumes and low cost, provide a sealed environment for the MEMS devices before they have to undergo singulation, and provide for electrical contacting of the MEMS device in addition to providing protection from environmental and process factors.

Testing and Reliability

In general, the answers to our questions about MEMS/MST testing and indicated little work is being done in this area at European university and research institutions. Most device researchers are looking to the users of MEMS/MST device technology to define reliability specifications, based on application requirements. The R&D groups only run some preliminary reliability tests and leave full qualification up to the industrial partner who wants to take the new microsystems products into manufacturing.

Of the groups we visited, TIMA has the most highly articulated definition of what needs to be done in the field of MEMS/MST reliability, and a vision of how to proceed, based on the prior model of the IC industry, but actual research work is not yet staffed at a high level. The basic conceptual framework is that testing and statistical analysis of device failures are important, but that they must be informed and organized within a framework based on an understanding of MEMS device behavior and physics of failure. TIMA follows a “bottom-up” approach, in which physical failure modes are first investigated, which leads to the development of models that can be used at different levels in the design hierarchy. The theoretical work should support the development of models of both faulty and fault-free behavior. While most modeling of MEMS takes place at the device or behavioral level, modeling which seeks to better explain device failure must take place at lower levels of granularity. In the view of Dr. Courtois (TIMA), the development of an adequate body of data and knowledge about device reliability in the MEMS domain is a long-term proposition, as it was in the early days of silicon integrated circuit technology.

Some of the concrete sources of failure in MEMS devices that TIMA has explored are stiction, breakage in mechanical fingers, and the effects of dust particles. TIMA researchers have examined sources of failure in devices fabricated through both the CMP and MUMPS services.

On the MST user side, Schlumberger representatives gave our team a well-defined account of their reliability requirements for MEMS devices and microsystems intended for use in oil and gas exploration. Within the Europractice network, Sintef (Norway), VTT (Finland), and NMRC (Ireland) are the primary organizations offering services in the testing and reliability field. The fact that our team did not visit any of these three may have impacted our view of work in MEMS reliability.


Fig. 4.7. Process flow for LETI “plip-chip” chip-scale package.


Published: January 2000; WTEC Hyper-Librarian