J.L. Lopez

Integrated CMOS-MEMS with on-chip readout electronics for high-frequency applications

A bridge-shaped first-lateral-mode 60-MHz mechanical resonator, which is monolithically integrated with capacitive CMOS readout electronics, is presented. The resonator is fabricated directly on a commercial CMOS technology using the top metal level as a structural layer. A maskless single-step wet-etching process for mechanical structure release after the standard CMOS integration process is the only postfabrication requirement. Electrical characterization of the electromechanical device demonstrates the feasibility of implementing a CMOS-microelectromechanical system for high-frequency applications using a standard conventional CMOS technology.

A CMOS–MEMS RF-Tunable Bandpass Filter Based on Two High-

This letter presents the design, fabrication, and demonstration of a CMOS-MEMS filter based on two high-Q submicrometer-scale clamped-clamped beam resonators with resonance frequency around 22 MHz. The MEMS resonators are fabricated with a 0.35-mum CMOS process and monolithically integrated with an on-chip differential amplifier. The CMOS-MEMS resonator shows high-quality factors of 227 in air conditions and 4400 in a vacuum for a bias voltage of 5 V. In air conditions, the CMOS-MEMS parallel filter presents a programmable bandwidth from 100 to 200 kHz with a <1-dB ripple. In a vacuum, the filter presents a stop-band attenuation of 37 dB and a shape factor as low as 2.5 for a CMOS-compatible bias voltage of 5 V, demonstrating competitive performance compared with the state of the art of not fully integrated MEMS filters.

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This paper presents the design, fabrication and characterization of microresonators exhibiting resonance frequencies in the VHF and UHF bands, fabricated using the available layers of the standard and commercial CMOS technology, AMS-0.35mum. The resonators are released in a post-CMOS process consisting on a maskless wet etching. A clamped-clamped beam with resonance frequency of 290 MHz exhibiting Q-factors of 970 in air and 2836 in vacuum is presented. The fabrication and design of a ring bulk acoustic resonator (RBAR) designed to operate at 1 GHz is described. Preliminary results on the electrical characterization show a resonance frequency of 1.04 GHz and a quality factor of 400 in air.

22-MHz Polysilicon Clamped-Clamped Beam Resonators

A novel technique for global packaging of MEMS devices using standard CMOS technology is presented. A MEMS polysilicon resonator is fabricated and on-chip packaged using two metal layers already available from the CMOS technology. A simple buffered HF wet etching process is performed in house to release the MEMS resonator while metal deposition is used to vacuum seal the zero-level package. Both post-processing steps are carried out on CMOS chips. The design of the metal layers is carefully done in order to avoid the degradation of the MEMS. The electrical frequency response of the resonator is used for testing the performance of the final package. Electrical measurements and physical characterization demonstrate proper performance of the MEMS resonator and package.

From VHF to UHF CMOS-MEMS monolithically integrated resonators

This paper focuses on the design, fabrication and characterization of polysilicon microresonators monolithically integrated in a CMOS standard technology (AMS 0.35 mum). The design is focused in on-plane flexural clamped-clamped beams to attain frequencies in the VHF range. Resonators are fabricated using two polysilicon layers separated by a thin silicon oxide layer. Polysilicon layers are used indistinctively for electrodes and resonator structure whereas 40 nm-thick silicon oxide layer defines the gap between resonator and electrodes. A maskless post-CMOS process is needed for releasing the movable structures. A monolithically integrated CMOS circuitry along with the resonator is implemented to increase its capacitive read-out signal. The characterization of the resonators has been done by two-terminal measurements by means of a network analyzer both in air and in vacuum, and complemented by mixing measurements. A Qxf product of 2times1011 MHz in vacuum is achieved.

Zero-level packaging of MEMS in standard CMOS technology

In this paper a self-oscillator based on a polysilicon free?free beam resonator monolithically integrated and packaged in a 0.35??m complementary metal?oxide?semiconductor (CMOS) technology is presented. The oscillator is capable of providing a 350?mVPP?sinusoidal signal at 25.6?MHz, with a bias polarization voltage of 7?V. The microelectromechanical systems (MEMS) resonator is packaged using only the back-end-of-line metal layers of the CMOS technology, providing a complete low-cost CMOS?MEMS processing for on-chip frequency references.

VHF CMOS-MEMS resonator monolithically integrated in a standard 0.35μm CMOS technology

The advantage of combining a stiff microcantilever coupled mechanically to a soft nano cantilever in terms of mass responsivity and readout capacitive detectability is presented. The large spring constant and coupling capacitance values of the microcantilever allow maximizing the detectability quantified in terms of motional resistance. The small effective mass of the nanocantilever provide to the whole system with an optimized mass responsivity. A figure of merit that accounts for both characteristics, mass responsivity and detectability, is defined, calculated from FEM simulations and measured from mass detection experiments, in order to demonstrate that the combined system improve the performance of the individual components.

Packaged CMOS?MEMS free?free beam oscillator

Clamped-clamped beam resonators are designed and fabricated in a 0.35µm CMOS commercial technology, using a simple one-step mask-less wet etching to release the MEMS structures. The resonator, with a 22MHz resonance frequency shows a Q value of 227 and 4400, when measured at atmospheric pressure and vacuum, respectively. This resonator is used as the main building block for filtering application. Using parallel filtering and differential on-chip CMOS amplification, the RF-CMOS-MEMS system forms a tunable band-pass filter with programmable bandwidth (from 100kHz to 200kHz), stop band rejections of 30 dB and shape factors at −20dB smaller than 3, providing comparable performance than other MEMS filters using specific technologies.

Coupling Resonant Micro and Nanocantilevers to Improve Mass Responsivity by Detectability Product

In this work, the characterization of the first lateral in-plane flexural mode DETF (Double Ended Tuning Fork) MEMS resonator integrated monolithically in a CMOS 0.35µm technology is done. This characterization is done with the same resonator stand-alone and with an integrated CMOS amplifier to obtain the handling dynamic range of the applied voltage (dc bias and ac signal) for a linear behavior of the resonator.

High Q CMOS-MEMS resonators and its applications as RF tunable band-pass filters

A monolithic mass sensor with attogram resolution in air conditions has been fabricated using a conventional 0.35-μm CMOS process. The mass sensor is based on an electrostatically excited resonating sub-micrometer scale cantilever integrated with full custom designed CMOS electronics for sensing purposes and to self-excite the cantilever allowing its use in system-on-chip applications. The devices have been calibrated obtaining an experimental sensitivity of around 6 × 10-11 g/cm2 Hz equivalent to 0.9 ag/Hz for locally deposited mass. The results reported in this paper represent an improvement from previous works in terms of sensitivity, resolution and fabrication process complexity.