C. Hibert

Modeling and design of a low-voltage SOI suspended-gate MOSFET (SG-MOSFET) with a metal-over-gate architecture

A novel MEMS device architecture: the SOI SG-MOSFET, which combines a solid-state MOS transistor and a suspended metal membrane in a unique metal-over-gate architecture, is proposed. A unified physical analytical model (weak, moderate and strong inversions) is developed and used to investigate main electrostatic characteristics in order to provide first-order design criteria for low-voltage operation and high-performance. It is demonstrated that the use of a thin gate oxide (<20 nm) is essential for a high C/sub on//C/sub off/ ratio (>100) and a low spring constant (<100 N/m) is needed for low voltage (<5 V) actuation. An adapted fabrication process is reported.

Silicon sacrificial layer dry etching (SSLDE) for free-standing RF MEMS architectures

A novel Silicon Sacrificial Layer Dry Etching (SSLDE) technique using sputtered amorphous or LPCVD polycrystalline silicon as sacrificial layers and a dry fluorine-based (SF/sub 6/) plasma chemistry as releasing process is reported with a detailed experimental study of the release etching step. The process is capable of various applications in surface micromachining process, and can be applied in fabricating RF MEMS switches, tunable capacitors, high-Q suspended inductors and suspended-gate MOSFETs. The developed SSLDE process can release metal suspended beams and membranes with excellent performance in terms of etch rate (up to 15 /spl mu/m/min), Si:SiO/sub 2/ selectivity and is fully compatible with standard MEMS processing equipment and CMOS post-processing.

Tunable, high aspect ratio pillars on diverse substrates using copolymer micelle lithography: an interesting platform for applications

We demonstrate the use of copolymer micelle lithography using polystyrene-block-poly(2-vinylpyridine) reverse micelle thin films in their as-coated form to create nanopillars with tunable dimensions and spacing, on different substrates such as silicon, silicon oxide, silicon nitride and quartz. The promise of the approach as a versatile application oriented platform is highlighted by demonstrating its utility for creating super-hydrophobic surfaces, fabrication of nanoporous polymeric membranes, and controlling the areal density of physical vapor deposition derived titanium nitride nanostructures.

Profile angle control in SiO/sub 2/ deep anisotropic dry etching for MEMS fabrication

We report a recent breakthrough to control profile angle for SiO/sub 2/ deep anisotropic dry etching (SDADE). Our study reveals that gas residence time is the key parameter to control profile angle. Moreover, we show that it is possible to control profile angle, SiO/sub 2/ etch rate and SiO/sub 2/ selectivity to Si mask independently. Finally, the optimized process has the following performances: angle profile: 89.8/spl deg/, SiO/sub 2/ etch rate: 500 nm/min, selectivity: 18:1.

The suspended-gate MOSFET (SG-MOSFET): a modeling outlook for the design of RF MEMS switches and tunable capacitors

This paper reports on the modeling and key design aspects of an innovative MEMS device: the suspended-gate MOSFET (SG-MOSFET). Based on the coupled-electromechanical equations describing the suspended gate actuation, we present the investigation of the pull-in voltages and of the capacitance switching and tuning ranges for RF applications. A quasi-analytical model is developed for the gate-to-substrate capacitance of the SG-MOSFET and then, validated by numerical simulation. A SPICE macromodel using a polynomial voltage-controlled source is validated for the DC simulation of the SG-MOSFET. Guide lines for the low-voltage design of an SG-MOSFET RF switch are detailed.

A novel RF MEMS technological platform

A novel MEMS technological platform for RF passive components, namely RF MEMS switches, tuneable capacitors and high-Q suspended inductors, is reported. The proposed process employs a metal (Al, AlSi or Cu) as active movable layer and amorphous silicon or polycrystalline silicon as sacrificial layers, providing multi-air-gaps. Various types of substrates like bulk silicon and SOI can be used. Full-dry releasing of suspended beams and membranes is performed with SF/sub 6/ or XeF/sub 2/, with unrivalled yield/reproducibility compared with any other wet etching techniques. The platform is used to validate new MEMS architectures and concepts, such as the suspended-gate MOSFET that can serve as both RF capacitive switches and tuneable RF capacitors.

High Quality Factor Copper Inductors on Wafer-Level Quartz Package for RF MEMS Applications

The paper proposes and validates a new doubly functional quartz wafer-level package concept for MEMS devices. In addition to the mechanical and environment protection, thick-Cu high-Q inductors for RF applications are made within the package processing. A double-side processing of a quartz wafer is reported. While the top side of the quartz is used to realize quartz-embedded horizontal plane Cu inductors, the bottom side is thermo-mechanically bonded on an active wafer using an SU8 photoepoxy semi-hermetic seal. A successful fabrication results in terms of very good adhesion of SU8 bonding, compatibility with fluorine plasma chemistry for MEMS release and very good RF performances (excellent quality factors, higher than 30 at 2 GHz, and self resonant frequency above 6 GHz) was demonstrated

Direct Etching of High Aspect Ratio Structures Through a Stencil

This paper reports the feasibility of the fabrication of high aspect ratio structures on substrates via dry etching through a stencil mask placed onto the sample. It demonstrates the possibility to use standard equipment and processes with this novel masking technique, which allows the patterning of fragile and pre-structured surfaces, and avoids the use of resist or additional coating of the sample, reducing costs and processing time. Aspect ratios as high as 13:1 and pattern transfer with a gap of 100 ¿m are demonstrated.

Two-Dimensional MEMS Stage Integrated With Microlens Arrays for Laser Beam Steering

A novel microelectromechanical stage with one uniaxial set of combs capable of 2-D actuation is presented. A polymer microlens array (MLA) is mounted vertically onto the stage. Driven at resonance, the stage deflects 124 μm out of plane and 34 μm in plane. Finally, laser beam steering is demonstrated using two cascaded MLAs.

Fabrication and electrical characterization of high performance copper/polyimide inductors

This paper presents fabrication and RF characterization results of spiral inductors fabricated using a developed damascene-like thick-copper/polyimide process module. This module has low thermal budget and is compatible with current IC interconnect architectures, making it suitable for CMOS above IC integration of high quality factor passive devices. Thick, high-conductive copper layers associated with low K polymers and high resistivity substrates can provide RF performances that cannot be achieved using conventional thin aluminum films on low-resistivity substrates. Peak quality factors of about 20 and exceeding 10 over a wide frequency range (1-6 GHz) are demonstrated, with a self-resonant frequency of about 10 GHz. Measurements and equivalent circuit extraction results are also presented and discussed.