J. Teva

Monolithic CMOS MEMS Oscillator Circuit for Sensing in the Attogram Range

This letter presents the design, fabrication, and demonstration of a CMOS/microelectromechanical system (MEMS) electrostatically self-excited resonator based on a submicrometer-scale cantilever with ~1 ag/Hz mass sensitivity. The mechanical resonator is the frequency-determining element of an oscillator circuit monolithically integrated and implemented in a commercial 0.35 mum CMOS process. The oscillator is based on a Pierce topology adapted for the MEMS resonator that presents a mechanical resonance frequency of ~6 MHz, a relative low quality factor of 100, and a large motional resistance of ~25 M. The MEMS oscillator has a frequency stability of ~1.6 Hz resulting in a mass resolution of ~1 ag (1 ag = 10-18 g in air conditions.

Ultrasensitive mass sensor fully integrated with complementary metal-oxide-semiconductor circuitry

Nanomechanical resonators have been monolithically integrated on preprocessed complementary metal-oxide-semiconductor (CMOS) chips. Fabricated resonator systems have been designed to have resonance frequencies up to 1.5 MHz. The systems have been characterized in ambient air and vacuum conditions and display ultrasensitive mass detection in air. A mass sensitivity of 4 ag/Hz has been determined in air by placing a single glycerine drop, having a measured weight of 57 fg, at the apex of a cantilever and subsequently measuring a frequency shift of 14.8 kHz. CMOS integration enables electrostatic excitation, capacitive detection, and amplification of the resonance signal directly on the chip.

Integration of RF-MEMS resonators on submicrometric commercial CMOS technologies

Integration of electrostatically driven and capacitively transduced MEMS resonators in commercial CMOS technologies is discussed. A figure of merit to study the performance of different structural layers and different technologies is defined. High frequency (HF) and very high frequency (VHF) resonance MEMS metal resonators are fabricated on a deep submicron 0.18 µm commercial CMOS technology and are characterized using electrical tests without amplification, demonstrating the applicability of the MEMS fabrication process for future technologies. Moreover, the fabricated devices show comparable performance in terms of Q × fres with previously presented MEMS resonators, whereas the small gap allows obtaining a low motional resistance with a single resonator approach.

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.

Design, fabrication, and characterization of a submicroelectromechanical resonator with monolithically integrated CMOS readout circuit

In this paper, we report on the main aspects of the design, fabrication, and performance of a microelectromechanical system constituted by a mechanical submicrometer scale resonator (cantilever) and the readout circuitry used for monitoring its oscillation through the detection of the capacitive current. The CMOS circuitry is monolithically integrated with the mechanical resonator by a technology that allows the combination of standard CMOS processes and novel nanofabrication methods. The integrated system constitutes an example of a submicroelectromechanical system to be used as a cantilever-based mass sensor with both a high sensitivity and a high spatial resolution (on the order of 10/sup -18/ g and 300 nm, respectively). Experimental results on the electrical characterization of the resonance curve of the cantilever through the integrated CMOS readout circuit are shown.

Monolithic mass sensor fabricated using a conventional technology with attogram resolution in air conditions

Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional 0.35μm complementary metal-oxide-semiconductor (CMOS) process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of 6×10−11g∕cm2Hz equivalent to 0.9ag∕Hz for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of 2.4×10−17g in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity.

From VHF to UHF CMOS-MEMS monolithically integrated resonators

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.

A platform for monolithic CMOS-MEMS integration on SOI wafers

A new platform for micro- and nano-electromechanical systems based on crystalline silicon as the structural layer in CMOS substrates is presented. This platform is fabricated using silicon on insulator (SOI) substrates, which allows the monolithic integration of the mechanical transducer on crystalline silicon while the characteristics of the structural layer are kept independent from the CMOS technology. We report the design characteristics, the fabrication process and an example of application of the CMOS SOI-MEMS platform to obtain a mass sensor based on a crystalline silicon resonating cantilever.

Longitudinal bulk acoustic mass sensor

A polycrystalline silicon longitudinal bulk acoustic cantilever is fabricated and operated in air at 51 MHz. A mass sensitivity of 100 Hz/fg (1 fg=10−15 g) is obtained from the preliminary experiments where a minute mass is deposited on the device by means of focused ion beam. The total noise in the currently applied measurement system allows for a minimum detectable mass of 0.5 fg in air.

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

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.