Jaume Esteve

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.

Electromechanical model of a resonating nano-cantilever-based sensor for high-resolution and high-sensitivity mass detection

A simple linear electromechanical model for an electrostatically driven resonating cantilever is derived. The model has been developed in order to determine dynamic quantities such as the capacitive current flowing through the cantilever-driver system at the resonance frequency, and it allows us to calculate static magnitudes such as position and voltage of collapse or the voltage versus deflection characteristic. The model is used to demonstrate the theoretical sensitivity on the attogram scale of a mass sensor based on a nanometre-scale cantilever, and to analyse the effect of an extra feedback loop in the control circuit to increase the Q factor.

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.

Test structures for ISFET chemical sensors

Simple test structures and measurements were studied for determining their usefulness for the online monitoring of the aging effects on pH ion sensitive field effect transistor (ISFET) chemical sensors used in automatic systems. Devices consisted of long drain and field transistors and metallic meanders. Current and capacitance measurements were carried out with standard instruments. Results showed that not all the test structures and their related parameters were equally sensitive, and in some cases tests at a high temperature were necessary to accelerate the desired effects. The metallic meander structure proved to be quite sensitive to epoxy-coating degradation. For dielectric passivating layers, the parasitic transistors also showed sensitivity, especially when electrolyte was heated.<<ETX>>

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.

Determination of micromechanical properties of thin films by beam bending measurements with an atomic force microscope

Micromechanical measurements have been performed with a beam bending based technique using an atomic force microscope (AFM). This technique combines a very high load resolution with a nanometric precision in the measurement of the cantilever deflection. It has been applied to the determination of the Youngs modulus of different micromachined structures as polysilicon and β-SiC cantilever beams. This has required the previous calibration of the technique. The different characteristics of the analysed structures determined the need to use different AFM probes, being the optimum measuring condition achieved when both the probe and the beam have similar force constants. The results obtained show the ability of the proposed technique for the micromechanical assessment of miniaturised structures, which is required for development and optimisation of advanced micromachining technologies.

Etching front control of strips for corner compensation

Abstract In this paper a scheme of convex corner compensation for etching in aqueous KOH using only strips is presented. Turns and branches are used to control the etching front on the strip surface for better compensation quality. The design rules as well as the effects of turning and branching on the effective compensation length are presented. The etching fronts on the bottom are investigated by experiment. Applications of the new structures are shown.

Piezoresistive accelerometers for MCM package

Describes the first steps carried out for the integration of piezoresistive accelerometers in an MCM-D (D-type multichip modules with flip-chip interconnection) package. The bulk micromachined accelerometer technology and its modification to comply with MCM-D packaging technology requirements are presented. The accelerometer technology is based on BESOI (Bond and Etch Back Silicon-On-Insulator) wafers. The main characteristic of this technology is the use of the buried silicon oxide layer as an etch stop and as a sacrificial layer. In addition, over-range protection and self-test systems are defined without any additional photolithographic step or process. The flip chip attachment requires solderable metals in the bump pads. In addition, a sealing ring has been defined around the movable parts of the sensors to protect them from the underfill used during the final packaging process. Cantilever beam accelerometers with a self-test system are presented as example of the combined technology. The design, simulation, fabrication and characterization of the devices prior to the MCM-D packaging are presented as well.

The use of ferrofluids in micromechanics

An introduction to ferrofluids in MEMS applications is presented. Ferrofluids are fluids with magnetic properties. By applying a magnetic field, the balance of forces within the ferrofluid is varied so that the magnetic fluid can move or apply pressure. These capabilities can be used in the field of the microsystems. In this work, we have obtained the typical values of pressure which can be expected from a ferrofluid. Using a piezoresistive pressure sensor, a pressure of 0.04 bar has been obtained.