Dirk De Bruyker

A novel external electrode configuration for the electrostatic actuation of MEMS based devices

A novel external electrode concept is introduced and compared with the conventional and often used parallel plate electrode scheme for the electrostatic actuation of micro-electromechanical devices. In contrast to conventional parallel plate actuation, the presented external electrode configuration allows controlled operation of electrostatic actuators over their entire range of motion by avoiding electrostatic instability. The test vehicle for studying deflection versus voltage is a cantilevered beam with a free end, i.e. the worst-case scenario from a stability standpoint. Modeling and fabrication of test devices is discussed and experimental results are presented.

Electrodeposited copper inductors for intraocular pressure telemetry

A microsystem for wireless long-term measurement of the intraocular pressure is presented. The sensing element is a novel distributed parallel-resonant inductive-capacative circuit, with a pressure-dependent resonance frequency. This circuit is based upon a twofold on-chip deposited inductor. The high Q inductor is deposited by electrodeposition of copper on a micromachined chip incorporating a pressure-sensitive diaphragm. Test structures were fabricated and characterized. Q factors of 30 at 45 MHz and inductance values of 0.4 µH are obtained for 3×3 mm2 structures.

Enthalpy array analysis of enzymatic and binding reactions

Enthalpy arrays enable label-free, solution-based calorimetric detection of molecular interactions in a 96-detector array format. The combination of the small size of the detectors and the ability to perform measurements in parallel results in a significant reduction of sample volume and measurement time compared with conventional calorimetry. We have made significant improvements in the technology by reducing the temperature noise of the detectors and improving the fabrication materials and methods. In combination with an automated measurement system, the advances in device performance and data analysis have allowed us to develop basic enzyme assays for substrate specificity and inhibitor activity. We have also performed a full titration of 18-crown-6 with barium chloride. These results point to future applications for enthalpy array technology, including fragment-based screening, secondary assays, and thermodynamic characterization of leads in drug discovery.

Measurement of enzyme kinetics and inhibitor constants using enthalpy arrays.

Enthalpy arrays enable label-free, solution-based calorimetric detection of molecular interactions in a 96-detector array format. Compared with conventional calorimetry, enthalpy arrays achieve a significant reduction of sample volume and measurement time through the combination of the small size of the detectors and ability to perform measurements in parallel. The current capabilities of the technology for studying enzyme-catalyzed reactions are demonstrated by determining the kinetic parameters for reactions with three model enzymes. In addition, the technology has been used with two classes of enzymes to determine accurate inhibitor constants for competitive inhibitors from measurements at a single inhibitor concentration.

Microspring Characterization and Flip-Chip Assembly Reliability

Electronics packaging based on stress-engineered spring interconnects has the potential to enable integrated IC testing, fine pitch, and compliance not readily available with other technologies. We describe new spring contacts which simultaneously achieve low resistance ( <; 100 mΩ) and high compliance (>; 30 μm) in dense 2-D arrays (180 ~ 180-μm pitch). Mechanical characterization shows that individual springs operate at approximately 150-μN force. Electrical measurements and simulations imply that the interface contact resistance contribution to a single contact resistance is <; 40 mΩ . A daisy-chain test die consisting of 2844 contacts is assembled into flip-chip packages with 100% yield. Thermocycle and humidity testing suggest that packages with or without underfill can have stable resistance values and no glitches through over 1000 thermocycles or 6000 h of humidity. This paper suggests that integrated testing and packaging can be performed with the springs, enabling new capabilities for markets such as multichip modules.

Rapid mixing of sub-microlitre drops by magnetic micro-stirring

We demonstrate rapid mixing of sub-microlitre droplets (250 nl) using miniaturized magnetic stir bars (400 μm × 200 μm × 15 μm). The stir bars are fabricated using laser micromachining and placed on the substrate on which the drops are manipulated. They are activated by an externally applied magnetic field and used in combination with on-demand drop merging in enthalpy arrays. This technique results in a 10-fold increase in mixing rate, and a mixing time constant of about 2 s. Drop mixing times are measured by Förster resonance energy transfer (FRET) and verified by thermodynamic measurements of binding and enzymatic reactions.

Vacuum Steered-Electron Electric-Field Sensor

In a new type of microelectromechanical system (MEMS) electric-field sensor, a sheet of electrons is thermionically emitted by a hot cathode, flows through a vacuum, and is collected by a pair of anodes 2000 μm away. As the electrons move through the vacuum, they are steered by external electric fields, resulting in a differential current at the anodes. The micromachined tungsten cathode has a low-work-function coating and is suspended over a cavity on a glass chip. These sensors have been operated both in a vacuum chamber and sealed in glass vacuum tubes. Measured sensitivities in a vacuum tube at 10,100, and 1000 Hz are 470, 230, and 140 mV/m·Hz1/2, respectively; sensitivities in a vacuum chamber at the same frequencies are 34, 6.3, and 2.4 mV/m·Hz1/2, respectively.

Vanadium oxide thermal microprobes for nanocalorimetry

Highly sensitive thermal microprobes are presented, consisting of curved cantilevers with vanadium oxide thermistors located at their tips. The cantilevers are realized by stress-engineered metal thin films and the thermistors consist of reactively sputter-deposited vanadium pentoxide. The thermistors are electrically contacted through the stressed metal layer, and at the same time thermally insulated from the substrate due to the relatively small thickness and large length of the cantilevers. We propose to apply these novel thermal microprobes in a nanocalorimetry system, in order to lower the cost and increase the sensitivity of the measurements.

Current crowding study of a micro spring contact for flip chip packaging

Current crowding of a micro spring pressure contact under high current is studied. The spring conducts > 250 mA electrical current between chips, has large mechanical compliance (> 30 µm) compared to other packaging technologies, and fits in a 180 µm pitch 2d array. At 250 mA and 65 °C, daisy chains of 134 spring contacts in a silicon package show stable resistances and hot spot temperature rises of less than a degree. At 1 A, failure near the spring tip or body is observed. Finite element modeling is performed to study the current density distribution and provide failure spot insight. A strategy is proposed to avoid current crowding.

The NanoPirani — Presumably the World’s Smallest Pressure Sensor

This abstract reports an extremely miniaturized pressure sensor, with an active area of a mere 10 × 1 µm2. Its working principle is similar to Pirani-type vacuum sensors. However, unlike vacuum sensors, the working range of the device is around atmospheric pressure.