Nicolas André

New On-Chip Nanomechanical Testing Laboratory - Applications to Aluminum and Polysilicon Thin Films

The measurement of the mechanical properties of materials with submicrometer dimensions is extremely challenging, from the preparation and manipulation of specimens to the application of small loads and extraction of accurate stresses and strains. A new on-chip nanomechanical testing concept has been developed in order to measure the mechanical properties of submicrometer freestanding thin films allowing various loading configurations and specimen geometries. The basic idea is to use internal stress present in one film to provide the actuation for deforming another film attached to the first film on one side and to the substrate on the other side. The measurement of the displacement resulting from the release of both films gives access to the stress and the strain applied to the test specimen provided the Youngs modulus and mismatch strain of the actuator film are known. Classical microelectromechanical-systems-based microfabrication procedures are used to pattern the test structures and release the films from the substrate. The design procedures, data reduction scheme, and a generic fabrication strategy are described in details and implemented in order to build a suite of test structures with various combinations of dimensions. These structures allow the characterization of different materials and mechanical properties and enable high throughputs of data while avoiding any electrical signal or external actuation. Results obtained on ductile aluminum and brittle polysilicon films demonstrate the potential of the method to determine the Youngs modulus, yield stress or fracture stress, fracture strain, and strain hardening in ductile materials.

Miniaturized Wireless Sensing System for Real-Time Breath Activity Recording

A portable, non-invasive and easy to operate wireless system has been developed for monitoring the breathing activity of patient. The system is composed of a capacitive microsensor (airflow-humidity sensor) integrated on a silicon chip and of a Negative Temperature Coefficient thermistor; both are connected to a wireless network to allow efficient healthcare at home as well as in hospitals. The capacitive sensitive part of the microsensor is an array of interdigitated metallic electrodes covered by 100-nm-thick dense anodized aluminum oxide layer. The breath water vapor is adsorbed over the interdigitated electrodes and changes the sensor characteristic capacitance by up to two orders of magnitude. This modulated signal is then digitized and either stored in a memory or directly transmitted to a monitor through a short distance radio frequency (RF) link. Results show that the wireless platform can be powered by two AAA batteries and deployed in a mesh or star configuration as wireless sensor network. Full size of the microsensor is less than 1 cm2 and is conveniently implemented in a classical adhesive bandage or in nasal prongs. This microsystem is proposed for monitoring sleep-disordered breathing as well as breathing rhythm of athletes during effort.

Three-Dimensional Self-Assembled Sensors in Thin-Film SOI Technology

A complementary metal-oxide-semiconductor (CMOS)-compatible one-mask process for the design and fabrication of three-dimensional (3-D) microelectromechanical systems (MEMS) sensors in thin-film silicon-on-insulator (SOI) technology is presented. The process relies on the control of the internal stresses in multilayered structures originating from thermal expansion mismatch between layers as well as on the control of the plastic yielding of a metallic layer. In contrast with techniques presented in the literature for the fabrication of 3-D MEMS, this process requires fabrication steps and machines fully compatible with a classical CMOS process and available in standard CMOS foundries. Preliminary characterization results of 3-D thermal and flow sensors based on capacitive sensing demonstrate the potential of this concept

Optimal overlayer inspired by Photuris firefly improves light-extraction efficiency of existing light-emitting diodes

In this paper the design, fabrication and characterization of a bioinspired overlayer deposited on a GaN LED is described. The purpose of this overlayer is to improve light extraction into air from the diodes high refractive-index active material. The layer design is inspired by the microstructure found in the firefly Photuris sp. The actual dimensions and material composition have been optimized to take into account the high refractive index of the GaN diode stack. This two-dimensional pattern contrasts other designs by its unusual profile, its larger dimensions and the fact that it can be tailored to an existing diode design rather than requiring a complete redesign of the diode geometry. The gain of light extraction reaches values up to 55% with respect to the reference unprocessed LED.

Silicon-on-Insulator Photodiode on Micro-Hotplate Platform With Improved Responsivity and High-Temperature Application

This paper reports on the performance of a silicon-on-insulator photodiode suspended on a dielectric membrane. The micro-hotplate platform consists of a micro-heater and a thin-film lateral P+/P-/N+ (PIN) photodiode. Without optimizing the multilayer stack on top of the PIN diode, experimental responsivities of the suspended photodiodes at room temperature (RT) are 0.02-0.06/W within the visible and near the IR light range, under a reverse bias of -2 V. Up to 2.5×, responsivity improvement has been achieved with regard to the diodes on the substrate thanks to reflection from the gold finish layer of the device package acting as a bottom mirror. Optimizing the layer stack above the diode, the responsivity of the on-membrane device can be theoretically improved up to 0.09-0.11 A/W within 450-520-nm wavelength range. Measured from RT up to 200 °C, the photodiodes on membrane continuously show an improved optical response under high-power LED illumination. Assisted by the micro-heater as heat source, the suspended photodiode can work stably up to 200 °C with in situ temperature sensing and control, which makes it highly suitable and attractive for high-temperature application. Full 2-D ATLAS device simulations have been comprehensively performed to investigate the optical and electrical characteristics. Very good agreement has been achieved between the numerical simulations and the experimental data.

One-mask CMOS compatible process for the fabrication of three-dimensional self-assembled thin-film SOI microelectromechanical systems

Multilayered self-assembled microstructures are built based on thin-film silicon-on-insulator (SOI) complementary metal-oxide-semiconductor (CMOS) compatible technology using a single mask process. The assembly relies on the chemical release of the microstructures and on the control of the residual stresses building up in multilayered structures undergoing a complete thermal process. The deflection of multilayered structures made of both elastic and plastic thin films results from the thermal expansion coefficient mismatches between the layers and from the plastic flow of a metallic layer. The process was successfully applied to 3-D self-assembled microstructures such as suspended meander inductors, thermal and flow sensors. (c) 2005 The Electrochemical Society.

Dew-Based Wireless Mini Module for Respiratory Rate Monitoring

Miniaturized humidity sensors combined with ZigBee transceiver and efficient data processing offer a powerful system for the monitoring of human breath. Every 10 ms, the expiration/inspiration phase is transmitted, allowing a medical diagnosis as efficient as required by the application. For the sensing system, a micro interdigitated capacitor, covered with a dense hydrophilic alumina layer, is connected to a capacitance-to-frequency circuit interface. A customized nasal canula-prototype embeds the microsystem underneath the patients nostrils while offering cabling until the belt-fixed radio transceiver. The fast data processing, executed in a mini notebook process unit, gives to the medical staff a live broadcast of the patients respiratory rate. In order to improve the size and the functionality of our sensing module, novel techniques for processing complementary metal oxide semiconductor (CMOS) in Silicon-on-Insulator (SOI) technology now allow for the construction of microsensors and CMOS circuits together on the same chip. These sensors consume extremely low power, of the order of 0.1 μW, present high sensitivity, occupy small chip area (1.25 mm2) and offer the prerequisite platform for a large variety of new sensors.

Wide band study of silicon-on-insulator photodiodes on suspended micro-hotplates platforms

In this paper, the performances of a lateral thin-film PIN photodiode based on silicon-on-insulator technology are reported for applications from blue to red wavelengths. The platform consists of a micro-hotplate with a suspended heater and a photodiode. Responsivities of 0.01 to 0.05 A/W were obtained for 450-900 nm light range in reverse bias operation. Suspended photodiodes give up to 5x responsivity improvement with regard to the photodiodes on substrate. In addition to photodetection, the diode can monitor the temperature with a linear voltage decreasing by about 1.4 mV/K, under 50 μA constant forward current for a large range of temperature (measured from 25 to 300°C).

Miniaturized and low cost innovative detection systems for medical and environmental applications

Innovative, simple, miniaturized, low-cost and low-power consumption devices are required in future medical applications. In our laboratory we have developed different devices in this field. Firstly, oxide aluminum-coated interdigitated (ID) Al capacitors have been successfully tested for DNA hybridization test (down to 30 pM target concentrations), as well as for specific bacteria recognition (S. Aureus, down to 100 CFU on a sensing area of 200×200 µm2) with an appropriate anti-monoclonal antibody (MoAb) and finally for humidity detection with application in a breath rate monitoring system, an important element for preventive medical studies, which is light, non-invasive, comfortable to wear for the patient. Secondly a complete microsystem enabling the measurement of biomolecules concentration in assay tubes has been developed based on ultraviolet (UV) light absorption with miniaturized LEDs and SOI high-efficiency photodiodes. Our technologies combine high-performance CMOS integrated circuits, sensors and MEMS; operation in harsh conditions (micro power, high-temperature, remote RF link, etc.); very low power consumption; and broad applications in biomedical and environmental sectors. This opens the door to many new emerging applications into medical devices.

CMOS compatible 3-D self assembled microstructures using thin film SOI technology

3D self-assembled microstructures are processed based on thin film SOI wafers. Self assembled structures going from meander inductors to flow sensors are obtained from using only one photolithographic step. The assembly of our microstructures relies on the thermal expansion mismatch between the material layers as well as control of the plastic flow of one of the layers.