C. Vancura

Characterization of magnetically actuated resonant cantilevers in viscous fluids

The vibration behavior of magnetically actuated resonant microcantilevers immersed in viscous fluids has been studied. A dependence of the resonance frequency and the quality factor (Q factor) on the fluid properties, such as density and viscosity and on the cantilever geometry is described. Various cantilever geometries are analyzed in pure water and glycerol solutions, and the results are explained in terms of the added displaced fluid mass and the fluid damping force for both the resonance frequency and the quality factor. An in-depth knowledge and understanding of such systems is necessary when analyzing resonant cantilevers as biochemical sensors in liquid environments.

Monolithic Resonant-Cantilever-Based CMOS Microsystem for Biochemical Sensing

A resonant cantilever-based microsystem aimed at biochemical sensing is presented. The sensor system comprises a magnetically actuated resonant cantilever sensor array integrated with the feedback circuitry, digital control circuitry and a serial interface on a single chip in 0.8 mum CMOS technology. The sensor system shows a frequency stability of better than 3 Hz in water corresponding to a detection limit of about 30 pg mass loading. The system has been used for the detection of antibody-antigen interaction on the cantilever surface. The possibility to actuate and operate cantilever arrays in a liquid environment opens up a variety of new applications for bio-chemical sensing.

Very high Q-factor in water achieved by monolithic, resonant cantilever sensor with fully integrated feedback

We present a novel, monolithic, mass-sensitive cantilever sensor for measurements in liquids, which achieves a high quality factor (Q-factor) by closed-loop actuation. The cantilever is the frequency-determining element in the feedback system, its resonance frequency being a function of the mass-change on the surface. While cantilever-based sensors generally suffer from low quality factors in liquids due to the strong damping, our device uses an internal feedback loop circuitry to enhance the Q-factor. This allows to increase Q-factor from 23 to 19,000 at a resonance frequency of 221 kHz. The cantilever is electromagnetically actuated by Lorentz force while the oscillation is detected by piezoresistive MOS-transistors. A fully differential feedback circuitry with amplitude control is integrated together with the cantilever on the same chip. Thanks to the high Q-factor and the resulting frequency stability, even small frequency (and mass) changes can be precisely measured by this fully integrated system. Therefore, active, external actuation or readout instrumentation, such as a laser for optical detection, is not required. The sensor is an excellent candidate for biosensing applications in liquids such as biomolecule hybridization and illustrates the advantage of integrated circuitry for resonant sensors.

Magnetically actuated CMOS resonant cantilever gas sensor for volatile organic compounds

We present a novel design of a resonant cantilever gas sensor for Volatile Organic Compounds (VOCs) in air. The cantilever is electromagnetically actuated, and the oscillation is detected with piezoresistive MOS-transistors. A fully differential feedback circuit is integrated together with the cantilever on the same chip. The whole system is fabricated in an industrial 0.8-/spl mu/m CMOS (Complementary Metal Oxide Semiconductor) process combined with subsequent micromachining. The cantilever is the frequency-determining element in the feedback system. Polymers are used as sensitive layers to assess VOC concentrations. The device exhibits less power dissipation of the cantilever as compared to earlier designs, which feature electrothermal actuation and readout via p-diffused resistors. The low power consumption enables the use of the sensor in portable devices.

Fully integrated CMOS resonant cantilever sensor for biochemical detection in liquid environments

We present a novel design of a fully integrated resonant cantilever sensor for biochemical detection in liquid environments. Four mass-sensitive, resonant cantilevers are monolithically integrated with a fully differential feedback circuit, a digital counter, and a digital I/sup 2/C interface. The entire system is fabricated in an industrial 0.8-/spl mu/m CMOS (complementary metal oxide semiconductor) process combined with subsequent micromachining. The cantilever with electromagnetic actuation and piezoresistive readout is the frequency-determining element in the feedback system. Detection of protein absorption on the cantilever has been shown with this system.

Monolithic CMOS multi-transducer gas sensor microsystem

This paper presents a monolithically integrated multi-transducer microsystem to detect organic and inorganic gases. The system comprises two polymer-based sensor arrays, a metal-oxide-based sensor array, driving and signal processing electronics and a digital communication interface. The chip is fabricated in industrial 0.8 /spl mu/m CMOS-technology with subsequent post-CMOS micromachining and operates at a supply voltage of 5 volt. The monolithic integration of different transducer types with associated driving and read-out circuitry significantly improves the discrimination capability of the system and reduces the packaging efforts.

Equivalent-Circuit Model for CMOS-Based Resonant Cantilever Biosensors

We present the modeling and characterization of a CMOS-based resonant cantilever biosensor operating in fluid environments. The device, which is fabricated in a 0.8-mum CMOS process with subsequent CMOS-compatible micromachining, consists of four resonant cantilevers (resonance frequency about 200 kHz in water) monolithically integrated with dedicated analog and digital signal processing and conditioning circuitry. The integrated cantilevers feature electromagnetic actuation and piezoresistive readout. In the first part of the paper an equivalent circuit model of the resonant cantilever is developed. The model allows a full characterization of the complete system comprising the cantilevers and the circuitry using commercial circuit simulation software. As will be shown, the presented model shows good agreement with actual measurements. At the end of the paper the application of the monolithic sensor system to the detection of prostate specific antigen (PSA) at clinically significant concentration levels will be presented.

Advanced chemical microsensor systems in CMOS technology [gas sensors]

We report on results achieved with three different chemical microsensor systems featuring three different types of transducers, all of which are monolithically integrated with associated driving and readout circuitry. The capacitive sensor which is sensitive to changes in dielectric properties of the polymer layer upon analyte absorption, and the cantilever which is sensitive to predominantly mass changes, are two polymer-based gas sensors. An on-chip integrated /spl Sigma//spl Delta/-converter is used to detect the minute capacitance changes of the capacitive sensor. The cantilever is magnetically excited and its vibration is detected using a piezoresistive Wheatstone bridge. Self-oscillation of the cantilever is achieved through monolithic integration of the feedback circuitry. The third transducer is a microhotplate-based gas sensor which relies on the resistance changes of a metal oxide upon gas exposure at an operation temperature of 300-400/spl deg/C. The ultimate goal is the monolithic integration of all the different transducers with driving and signal-processing electronics and a digital communication interface on the same single chip.