Micromechanical resonators with sub-micron gaps filled with high-k dielectrics

Mariazel de la Candelas Maqueda López
EPFL, 2017
Thèse EPFL

Résumé

Scaled microelectromechanical (MEMS) resonating devices have generated a great interest for their use in RF front-end architectures for wireless communication, channel-select filters, on-chip signal processing and timing and extreme mas sensing applications thanks to their robustness, low power consumption, easy integration with CMOS and multimode reconfigurability. Therefore, MEMS resonators are a promising alternative to various discrete electrical components, offering excellent figures of merit at in the HF/VHF frequency range. However, there are many remaining open challenges for the research on MEMS resonators such as high quality factor at high frequency, thermal stability, reduced motional resistance, frequency precision and stability, low phase noise and appropriate hermetical and low cost packaging. Many advanced MEMS resonators use deep sub-micron air gaps (

Official source

https://infoscience.epfl.ch/record/230350?ln=fr

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Concepts associés

Chargement

Publications associées

Chargement

Nanogap MEM resonators on SOI

Nicoleta-Diana Ciressan

Today's consumer electronics based on a large variety of time-keeping and frequency reference applications is based on quartz-crystal oscillators, because of their excellent performances in terms of quality factor, thermal and frequency stability. However, macroscopic size and CMOS incompatibility of quartz-crystal resonators draw a major limit on the miniaturization of wireless communication applications. For this reason, silicon microelectromechanical (MEM) resonators are considered promising candidates to replace quartz-oscillators in VLSI communication systems, due to their compactness, design flexibility and CMOS process compatibility. This work reports on the design, fabrication and characterization of MEM bulk lateral resonators with resonance frequencies in the order of tens of MHz. The need of stable, low cost and high yield processes for fabricating devices with extremely narrow (sub 100 nm) transduction gaps is a main research driver, together with the requirements of improved designs which include high quality factors and appropriate power handling. We are investigating two major designs: (1) longitudinal beam resonators and (2) novel fragmented-membrane resonators that respond to both high quality factor (Q) and low motional resistance (Rm) requirements. We propose several design optimizations for solving some of the issues which currently affect the MEM resonator performance, like the frequency stability and Q enhancement through energy loss minimization. An original fabrication process is presented, which enables the manufacturing of SOI-based, fully monocrystalline devices with 100 nm transduction gaps and aspect ratios as high as [60:1], without the need of advanced lithography techniques. We successfully validate the fabrication process on two different SOI substrates, with silicon film thicknesses of 1.5 µm and 6.25 µm. This thickness range combined to the doping level corresponds to partially depleted SOI, which can be a substrate of choice for the fabrication of future integrated hybrid MEMS-CMOS integrated circuits for communication applications. The fabricated structures are successfully characterized, demonstrating excellent resonator performance at room temperature. Q's as high as 235'000 and Rm's as low as 59 kΩ have been extracted in vacuum. Atmospheric pressure frequency response measurements of the fragmented membrane resonators show Q's of 3'600. This value is among the best reported to date, opening the possibility for atmospheric pressure applications such as mass-detection for gas sensing applications with detection done without a special package, just by direct exposure of the resonator to the environment. A novel study on temperature dependence (between 80 K and 320 K) of the fragmented membrane resonators is presented and discussed. Significant Q increase and Rm reduction are experimentally observed at cryogenic temperatures. The bulk mode resonators developed and discussed in this thesis can successfully be integrated in oscillator circuits, as we demonstrate by simulating a Pierce topology based on the calibrated equivalent circuit model of a 24.48 MHz fragmented membrane BLR. Our oscillator shows very good phase-noise performance of -142 dBc/Hz at 1 kHz offset from the carrier and the noise floor at -144 dBc/Hz, which nearly meets the GSM specifications.

EPFL2009

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

Chargement

, , ,

Nanoelectromechanical systems (NEMS) as integrated components for ultrasensitive sensing, time keeping, or radio frequency applications have driven the search for scalable nanomechanical transduction on-chip. Here, we present a hybrid silicon-on-Insulator platform for building NEM oscillators in which fin field effect transistors (FinFETs) are integrated into nanomechanical silicon resonators. We demonstrate transistor amplification and signal mixing, coupled with mechanical motion at very high frequencies (25-80 MHz). By operating the transistor in the subthreshold region, the power consumption of resonators can be reduced to record-low nW levels, opening the way for the parallel operation of hundreds of thousands of NEM oscillators. The electromechanical charge modulation due to the field effect in a resonant transistor body constitutes a scalable nanomechanical motion detection all-on-chip and at room temperature. The new class of tunable NEMS represents a major step toward their integration in resonator arrays for applications in sensing and signal processing.

2011

Chargement

Nanogap MEM resonators on SOI

Nicoleta-Diana Ciressan

EPFL2009

EPFL2007