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Design and fabrication aspects of an S-shaped film actuator based DC to RF MEMS switch
KTH, Superseded Departments, Signals, Sensors and Systems.
KTH, Superseded Departments, Signals, Sensors and Systems.ORCID iD: 0000-0001-9552-4234
2004 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 13, no 3, 421-428 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on design and fabrication aspects of a new microelectromechanical series switch for switching de and RF signals. The switch consists of a flexible S-shaped film with the switching contact, rolling between a top and a bottom electrode in electrostatic touch-mode actuation. This design allows a low actuation voltage independent of the contact distance in the off-state. With a large contact distance, large overlapping switching contact areas are possible by obtaining a high off-state isolation. The RF transmission line and the MEMS part of the switch are fabricated on separate wafers, allowing an implementation of the switch with different RF substrates. The final assembly is done on device level for the first prototypes, even though the design provides the possibility of an assembly by full wafer bonding, leading to a near-hermetic package integrated switch. The measured prototype actuation voltages are 12 V to open and 15.8 V to close the contacts, with a resistance of 275 mOmega of each contact at an estimated contact force of 102 muN. The measured RF isolation with a contact distance of 14.2 mum is better than -45 dB up to 2 GHz and -30 dB at 15 GHz, at a large nominal switching contact area of 3500 mum(2).

Place, publisher, year, edition, pages
2004. Vol. 13, no 3, 421-428 p.
Keyword [en]
film actuator, low-stress silicon nitride, MEMS switches, RF MEMS, touch-mode actuation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-13414DOI: 10.1109/JMEMS.2004.828723ISI: 000221845700005ScopusID: 2-s2.0-3142685987OAI: diva2:325299
QC 20100617Available from: 2010-06-18 Created: 2010-06-17 Last updated: 2011-10-26Bibliographically approved
In thesis
1. Novel RF MEMS Switch and Packaging Concepts
Open this publication in new window or tab >>Novel RF MEMS Switch and Packaging Concepts
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Radio-frequency microelectromechanical systems (RF~MEMS) are highly miniaturized devices intended to switch, modulate, filter or tune electrical signals from DC to microwave frequencies. The micromachining techniques used to fabricate these components are based on the standard clean-room manufacturing processes for high-volume integrated semiconductor circuits. RF~MEMS switches are characterized by their high isolation, low insertion loss, large bandwidth and by their unparalleled signal linearity. They are relatively simple to control, are very small and have almost zero power consumption. Despite these benefits, RF~MEMS switches are not yet seen in commercial products because of reliability issues, limits in signal power handling and questions in packaging and integration. Also, the actuation voltages are typically too high for electronics applications and require additional drive circuitry.

This thesis presents a novel MEMS switch concept based on an S-shaped film actuator, which consists of a thin and flexible membrane rolling between a top and a bottom electrode. The special design makes it possible to have high RF isolation due to the large contact distance in the off-state, while maintaining low operation voltages due to the zipper-like movement of the electrostatic dual-actuator. The switch comprises two separately fabricated parts which allows simple integration even with RF circuits incompatible with certain MEMS fabrication processes. The two parts are assembled by chip or wafer bonding which results in an encapsulated, ready-to-dice package. The thesis discusses the concept of the switch and reports on the successful fabrication and evaluation of prototype devices.

Furthermore, this thesis presents research results in wafer-level packaging of (RF) MEMS devices by full-wafer bonding with an adhesive intermediate layer, which is structured before bonding to create defined cavities for housing MEMS devices. This technique has the advantage of simple, robust and low temperature fabrication, and is highly tolerant to surface non-uniformities and particles in the bonding interface. It allows cavities with a height of up to many tens of micrometers to be created directly in the bonding interface. In contrast to conventional wafer-level packaging methods with individual chip-capping, the encapsulation is done using a single wafer-bonding step. The thesis investigates the process parameters for patterned adhesive wafer bonding with benzocyclobutene, describes the fabrication of glass lid packages based on this technique, and introduces a method to create through-wafer electrical interconnections in glass substrates by a two-step etch technique, involving powder-blasting and chemical etching. Also, it discusses a technique of improving the hermetic properties of adhesive bonded structures by additional passivation layers. Finally, it presents a method to substantially improve the bond strength of patterned adhesive bonding by using the solid/liquid phase combination of a patterned polymer layer with a contact-printed thin adhesive film.

Place, publisher, year, edition, pages
Stockholm: KTH, 2004. xii, 142 p.
Trita-ILA, ISSN 0281-2878 ; 0401
0-level packaging, adhesive bonding, BCB, benzocyclobutene, bond strength, contact printing, film actuator, glass lid encapsulation, glass lid packaging, helium leak test, hermetic packaging, hermeticity, high isolation switch, low stress silicon nitride, low volt
National Category
Engineering and Technology
urn:nbn:se:kth:diva-3817 (URN)91-7283-831-0 (ISBN)
Public defence
2004-09-10, 00:00
QC 20100617Available from: 2004-08-26 Created: 2004-08-26 Last updated: 2010-06-18Bibliographically approved

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