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Prominent - Processes for MEMS by Inkjet Enhanced Technologies

The objective of the ENIAC JU project PROMINENT was to demonstrate significant cost reduction in MEMS manufacturing by using printing technologies to reduce materials, chemicals and energy consumption, waste water production, processing cycle time and capital investments.

Now in June 2016, PROMINENT is ending. In mid-June Prominent results were presented to the Experts chosen to review the project, to the ECSEL JU Programme Officer, and to the National Observers in Tampere, Finland. Before the review meeting in March, last Prominent General Assembly meeting was held in Horten, Norway.

The updated list of conference presentations, journal articles and other dissemination activities are collected to the prominent Press&Conference website.

Below, the achievements of Prominent, during the last period and during the whole project are summarised.

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Prominent during the last period

During the third period the project focus was laid on to complete the demonstrators. Notable achievements were attained in ink-jet deposition of protective layers in MEMS fabrication, conductive interconnects between layers, RDLs, and self-assembling TSVs as well as techniques of gettering and realization of controlled pressures in structures.  A detailed cost analysis and a tailorable software tool were finished to compare different process flows and cost differences of the ink-jet processes compared to more conventional techniques.

FO-WLP packaging of two different kinds of functional MEMS devices, one having an opening to ambient, was demonstrated. With the method low-cost very-thin MEMS devices can be made in volumes without being limited to completely sealed packages.   Furthermore, MEMS autofocus lens development was successfully completed and demonstrated. This device has faster focusing speed and lower energy consumption compared to existing devices in the market. 

Ink-jet technology offers attractive possibilities on MEMS manufacturing being additive, maskless process with potential cost savings. However, ink formulations play a crucial role  – in each application there are some unique requirements, like purity of the deposited material after curing or stability of the material.

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Prominent results achieved during the project

After the three years and four months’ project, as a general observation and as one of the results of the project it can be summarised that ink formulations influence strongly the ink-jet printing results, and in each application there are several unique requirements, possibly making standard off-the-shelf inks unsuitable for the desired purposes or their performances are not necessarily at the optimum. In other words, inks (and stability of nanoparticles), especially with reactive materials, like silicon, titanium or copper, need further development. Despite of this,

• RDL (redistribution lines) applicable to MEMS devices with ink-jet printing,

• ink-based interconnects in SOI wafers (related patent application pending),

• wafer-to-wafer bond frames deposited with metal inks, and

• additive etch mask manufacturing avoiding normal lithography steps

were all demonstrated.

Some of these results can after minor development efforts be transferred into production especially now when – unlike during the planning phase of the project – ink-jet tools capable of handling silicon wafers cassette-to-cassette, are available. The tools also accept the plasma activation head introduced and developed by partner Innophysics in the project. Innophysics’ device can modify wafer surfaces locally in order to influence the wettability of the ink at the surface. This way it is possible to draw very fine ink lines on silicon, and it is also possible to fill cavities or TSV´s without over-spilling the ink.

Partner Silex demonstrated together with partner KTH novel TSV and TGV concepts. In addition, Silex demonstrated a gettering process suitable for MEMS devices, and, invented and developed a novel method for multiple pressures suitable for WLP-based MEMS packaging for example for combo sensors. This beyond the state-of-the-art technology was validated by Silex with realistic test structures giving a pressure difference up to 4 orders of magnitude in a same MEMS die (1 Pa vs 104 Pa).  A patent application was filed by Silex in 2014, and was granted just before the end of the project. Silex developed a new wafer level capping technology for RF MEMS using innovative novel TGV in glass showing very high linearity and low RF losses, and during 2016 Silex started to commercialize it.

To our best understanding, in this project partners Murata and Nanium demonstrated the very first FO-WLP packaged inertial and pressure sensors.  FO-WLP offers ways to make very thin, < 0.5...0.6 mm of thickness, sensor packages.  Furthermore, in the project, Murata introduced a piezo-actuated inertial sensor platform successfully.

Partner poLight developed and demonstrated TLens, a novel piezo-actuated autofocus lens for mobile communication. The device is faster than conventional designs, and also the current consumption is greatly reduced compared to existing solutions. The implementation of the lens, for commercial production at a foundry, was done in other Eniac JU project (Lab4MEMS) successfully. In this project NANIUM designed a FO-WLP Process Flow for hollow dies integration.

 As a summary, most far-reaching targets were achieved partially, and need further development and close collaboration with nanoparticle and ink manufacturers, but a considerable part of the results is applicable in commercial production while some results are even ground-breaking achievements.

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Summer Greetings,

As this is now the last Prominent-Newsletter, the consortium wishes to thank you, as a subscriber and a reader of the Newsletter, for the attention and wish you a relaxing summer 2016.

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