Guided-wave micro-electro-mechanical systems (MEMS) optical switches for telecommunication applications

Roland Guerre
EPFL, 2005
Thèse EPFL

Résumé

The present thesis deals with Micro-Electro-Mechanical Systems (MEMS) optical switches for telecommunication applications. The aim is to study new type of microsystems for guided-wave optical switching applications. Two projects have been investigated. The first part addresses a novel technological and design study of N×N optical switch integration with planar waveguides and vertical displacement micro-mirrors. Novel suspended MEMS mechanical platform on SOI wafer were designed and realized and technological processes for optimization of micro-mirrors quality have been developed. The motivation of this study was related to initial collaboration with the company Memscap S.A. which was looking for compact and fast N×N optical switches based on planar waveguides. One of the key issue being waveguide integration, a concept of a hermetic packaging with two wafers assembly where a waveguide wafer is placed face down on top of MEMS electrostatic devices with vertical micro-mirrors has been developed. Vertical micro-mirrors have been fabricated in SU8 photopolymer or in single crystalline silicon. For integration of silicon mirrors, a new simple two-steps DRIE pattern transfer that allow simultaneous fabrication of good quality silicon mirrors and of recessed mechanical platform has been demonstrated. The platform has been analysed through its resonance behaviour. The strong effect of mechanical non-linearity which was observed in clamped suspension can be exploited to increase the control range of the electrostatic actuator. During the first part of this work on MEMS optical switches based on planar waveguides, a totally new approach that use hollow waveguide instead of solid core waveguide has been developed. The primary motivation was whether it was possible to integrate a micromechanical switch composed of a vertical silicon cantilever beam mechanism inside the air core of the hollow waveguide. Silicon Planar Hollow Waveguides (PHW) have been designed, realized and tested with different optical coatings: a metallic gold coating, dielectric bilayers based on the principle of AntiResonant Reflective Optical Waveguide (ARROW) and bare silicon. The influence of ARROW layers on hollow planar waveguides has been investigated. The very first PHW with integrated 1×2 optical switching have been manufactured and characterized. Switching times better than 10 μs were measured with the produced devices. The switching speed was about 100 times higher to other MEMS optical switches based on micro-mirrors.

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https://infoscience.epfl.ch/record/49875?ln=fr

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Roland Guerre
EPFL, 2005
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/49875?ln=fr

À propos de ce résultat

Concepts associés (11)

Concepts associés

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Publications associées (4)

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Resonating large angle and low consumption micromachined optical scanner

Philippe Renaud, Sandra Schweizer

A monolithic silicon integrated optical micro-scanner is presented. The device consists of a mirror located an the tip of a thermal bimorph actuator beam. The fabrication process is very simple and compatible with IC fabrication techniques. The device is excited electrothermomechanically at its resonance frequency, enabling large angular deflections at low power consumption. The technological process consists of basic frontside silicon micromachining steps requiring only three mask levels. The moving part is defined by selective silicon bulk etching. The bimorph beam is made of silicon dioxide and a thin film conductor. The residual stress in the two layers is used to achieve a 45 degrees out-of-plane rest position of the mirror. This allows optical components (e.g, laser diode, collimating lens) to be placed directly on the silicon substrate. Mirrors of 500300 and 1000500 mu m(2) with resonant frequencies at 300 and 100 Hz respectively were realized. Mechanical scan angles of above 90 degrees were acheived. The devices are very robust and have run through fatigue tests of billions of cycles at 300 Hz and 90 degrees deflection. The power consumption of the device is typically 1mW for 30 degrees mechanical scan angles.

1998

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Thermally actuated optical microscanner with large angle and low consumption

Philippe Renaud, Sandra Schweizer

A monolithic silicon integrated optical micro-scanner is presented. The device consists of a mirror located on the tip of a thermal bimorph actuator beam. The fabrication process is very simple and compatible with IC fabrication techniques. The device is excited electrothermally at its resonance frequency, enabling large angular deflections at low power consumption. The technological process consists of basic frontside silicon micromachining steps requiring only three mask levels. The moving part is defined by selective silicon bulk etching. The bimorph beam is made of silicon dioxide and a thin film conductor. The residual stress in the two layers is used to achieve a 45 degrees out-of-plane rest position of the mirror. This allows optical components (e.g., laser diode, collimating lens) to be placed directly on the silicon substrate. Mirrors of 500 x 300 to 800 x 800 mu m(2) with resonant frequencies varying from 600 to 100 Hz were realized. Mechanical scan angles of above 90 degrees were achieved. The devices are very robust and have run through fatigue tests of billions of cycles at 300 Hz and 90 degrees deflection. The power consumption of the device is typically 1 mW for 30 degrees mirror deflection. (C) 1999 Elsevier Science S.A. All rights reserved.

1999

Chargement

Wireless communication systems and handset devices are showing a rapid growth in consumer and military applications. Applications using wireless communication standards such as personal connectivity devices (Bluetooth), mobile systems (GSM, UMTS, WCDMA) and wireless sensor network are the opportunities and challenges for the semi-conductor industry. The trend towards size and weight reduction, low power consumption and increased functionalities induces major technological issues. Today, the wireless circuit size is limited by the use of lots of external or "off-chip" components. Among them, quartz crystal, used as the time reference in any wireless systems, is the bottleneck of the miniaturization. Microelectromechanical systems (MEMS) is an emerging technology which has the capability of replacing the quartz. Based on similar technology than the Integrated Circuit (IC), MEMS are referred as electrostatically, thermally or piezoelectrically actuated mechanical structures. In this thesis, a new MEMS device based on the hybridization of a mechanical vibrating structure and a solid-sate MOS transistor has been developed. The Resonant Suspended-Gate MOSFET (RSG-MOSFET) device combines both advantages of a high mechanical quality factor and the transistor intrinsic gain. The physical mechanisms behind the actuation and the behavior of this device were deeply investigated and a quasi-static model was developed and validated, based on measured characteristics. Furthermore, the dynamic model of the RSG-MOSFET was created, taking into account the non-linear mechanical vibrations of the gate and the EKV model, used for MOSFET modeling. Two fabrication processes were successfully developed to demonstrate the proof of concept of such a device and to optimize the performances respectively. Aluminum-silicon (Al-Si1%) and pure silicon-based RSG-MOSFETs were successfully fabricated. DC and AC characterizations on both devices enabled to understand, extract and evaluate the mechanical and MOSFET effects. A specifically developed RF characterization methodology was used to measure the linear and non-linear behaviors of the resonator and to evaluate the influence of each polarization voltages on the signal response. RSG-MOSFET with resonant frequencies ranging from 5MHz to 90MHz and quality factor up to 1200 were measured. Since MEMS resonator quality factor is strongly degraded by air damping, a 0-level thin film vacuum packaging (10-7 mBar) process was developed, compatible with both AlSi-based and silicon-based RSG-MOSFET. The technology has the unique advantage of being done on already released structure and the room temperature process makes it suitable for above-IC integration. In parallel, a front-end compatible process was defined and major build blocks were developed in industrial environment at STMicroelectronics. This technology is based on the Silicon-On-Nothing technology, originally developed for advanced transistor, and therefore making the MEMS resonator process compatible with CMOS co-integration. DC characterizations of SG-MOSFET had shown interesting performances of this device for current switch and memory applications. Mechanical contact of the gate with the MOSFET channel induces a current switching slope greater than 0.8mV/decade, much better than the theoretical MOSFET limit of 60mV/decade. Maximum switch isolations of -37dB at 2 GHz and -27dB at 10GHz were measured on these devices. A novel MEMS-memory has been demonstrated, based on the direct charge injection to the storage media by the mechanical contact of the metal gate. Charge injection and retention mechanisms were investigated based on measured devices. Cycling study of up to 105 cycles were performed without noticing major degradations of the electrical behavior neither mechanical fatigue of the suspended gate. The measured retention time places this memory in between the DRAM and the FLASH memories. A scaling study has shown integration and compatibilities capabilities with existing CMOS.

EPFL2007

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EPFL2007