ERC for Wireless Integrated MicroSystems (WIMS) an NSF-University-Industry Collaboration

Bulk piezoelectric ceramics provide greater electromechanical coupling, structural strength, and charge capacity compared to deposited piezoelectric thin films (e.g., sol-gel PZT or sputtered AlN). Such properties are highly desirable in many MEMS applications including high-force actuators and micropower scavengers.

Resonant magnetoelastic sensors have been developed for wireless sensing of viscosity changes and sludge accumulation in biliary stents. The sensing element, located within the stent, is queried by a wireless radiofrequency signal. The stent has a conformal magnetic layer that biases the sensor.

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful analytical technique to separate and detect the components of complex mixtures of volatile organic compounds. Focusing and reinjecting eluting mixture components, a thermal modulator placed between two separation columns in a GC×GC system plays a critical role in enhancing the resolution and the selectivity of analytes.

We have monolithically integrated optical waveguides on the neural probe shanks for the first time in order to guide light to designated sites close to recording electrodes. This will harness additional capability to selectively stimulate the specific targeted neurons that are genetically modified to respond to light at a specific wavelength.

High-force, large-deflection actuators are critical for devices such as valves and pumps used in micro-fluidic systems, for surface bump manipulation in tactile displays, and for micro-airfoil control. However, existing transduction methods such as piezoelectric, electro-magnetic, or electrostatic are limited in their ability to provide such actuation in low-power integrated microsystems.

The first Orion CVD-sealed and released microcolumns have recently been fabricated, coated, and successfully used to separate gaseous mixtures. The Orion micro gas chromatography system is being developed by the WIMS ERC to explore the scaling limits in such systems. The very low mass of these columns allows high-speed temperature programming and their high thermal isolation substantially reduces their operating power.

With the completion of the Human Genome Project and the sequencing of several other scientifically important genomes, emphasis has shifted to determining the structure and function of the gene products, i.e., the proteins. The goal of this multidisciplinary project is to develop an integrated microsystem platform that incorporates a protein-based bio-interface array into a continuous-use, cost-effective, electrochemical characterization system suitable for functional proteomics research.

With advances in CMOS technology, significant progress has been realized in implementing multichannel, implantable neural systems that will potentially enable us to diagnose disease and establish a direct interface between the brain and external electronic devices. However, chronic monitoring of brain activities, such as neural spikes, EEG, ECoG, etc., is still a challenge, especially in wireless ambulatory systems, due to stringent constraints in power, noise, and area.

Cochlear implants for the deaf are the most successful of all neural prostheses; however, pitch perception remains relatively poor due to wire limitations. Commercial wire-bundle cochlear arrays are limited to about twenty wires (sites) by the size of the scala tympani into which the arrays must be inserted.

Low-power, small-size analog-to-digital converters (ADC) have numerous applications in areas ranging from power-aware wireless sensing nodes for environmental monitoring to biomedical monitoring devices in point-of-care (PoC) instruments. Despite continued improvements to ACDs in recent years, we still strive to make them smaller and more power efficient.

In response to the need for ever-better methods of screening passengers and luggage for concealed explosives at transportation terminals, we are developing microsystems that can rapidly differentiate markers of nitro-aromatic explosives (e.g., TNT) from background interferences at trace concentrations in ambient air. The INTREPID prototype (upper left panel) is a gas chromatographic microsystem (µGC) designed to rapidly capture, preconcentrate, inject, separate, and selectively detect targeted marker compounds.

Carbon nanotubes (CNTs) are seamless hollow cylinders that have unique and exceptional mechanical, thermal, electrical, and chemical properties. Our ability to fabricate highly organized CNT assemblies, having critical dimensions ranging from micron to milli-meter scales, offers opportunity to harness the properties of CNTs in MEMS devices.

The SAR analog-to-digital conversion architecture is popular because of its energy efficiency; however, the SAR architecture is less used for resolutions above 10b. A two-comparator architecture, incorporating deliberate comparator offset and pre-amplifier power management, reduces comparator metastability and comparator power consumption in a 12b 11MS/s SAR ADC.

Advances in neuroscience depend on the availability of supporting technology for the high-density stimulation and recording of neural activity. An important area of research focuses on the cochlear nucleus (CN) of the auditory pathway, where details of the connections between the anterior ventral cochlear nucleus (AVCN) and the dorsal cochlear nucleus (DCN) are yet to be fully understood.

High-temperature pressure sensors have uses in numerous industrial sectors including gas turbine engines, coal boilers, internal combustion engines, and oil/gas exploration machinery. These environments require durable sensors, making sensors without moving parts and without intermediate transduction steps advantageous. To meet these challenges, microdischarge-based pressure sensors have been developed.

A new process has been developed for fabricating silicon-glass microsystems such as the implantable intraocular pressure sensor now being pursued by the WIMS ERC. The process allows the realization of glass die of arbitrary two-dimensional shape containing silicon (or metal) feedthroughs as small as 20µm in diameter. Shaping glass and producing feedthroughs in it are both long-standing problems in MEMS.

This study was designed to investigate whether a non-penetrating microwire device can serve as a brain machine interface (BMI) for a motor neural prosthesis. These devices offer higher spatial and temporal resolution than standard electroencephalography or electrocorticography electrode arrays without penetrating the neocortex.

Brain machine interfaces have been recognized as a powerful tool in helping patients with neural disorders. Wireless transmission of potentially hundreds of signals to extracranial processing units must address three major limitations: bandwidth, implant area, and power consumption. For example, without compression, a 32-channel system with a sampling rate of 25KHz per channel and 10-bits of data precision generates data at 8Mbps.

Micromachined Joule-Thomson (J-T) coolers have applications ranging from cryosurgery to cooling infrared detectors in space and portable applications. The counter-flow recuperative heat exchangers in the J-T coolers must maintain good stream-to-stream heat conductance while restricting stream-wise conduction in order to achieve a high effectiveness and allow a large enthalpy difference between the two streams.

The average power consumption of sensor platforms, which are often low duty cycle, can be greatly reduced by applying strong power gating while idling. A key component in power gating is the timekeeping device while the system is in the idle mode. Since the timekeeping device, or timer, is always active, it is often the dominant source for energy loss and must oscillate at a low frequency (e.g., from sub-Hz to 10Hz). Crystal oscillators are too expensive and large for tiny sensor platforms, and typical watchdog timers consume uW of power, which is too high.

One of the key components in neural prosthetic systems is the microprobe, which is responsible for interfacing with neurons. This project aims to design and fabricate a novel all-diamond neural probe. Polycrystalline diamond is used as the material for the probe shank, interconnects/leads, and electrodes. Diamond is chosen because of its unique properties. It has one of the largest Young’s moduli (~1011Pa) of all known materials.

A key challenge in realizing implantable multi-electrode microsystems for neural interface applications is the integration of the front-end electrodes with their interface circuitry. A low profile is important to allow the dura to be replaced over the implant, decoupling it from the skull and allowing it to move with the brain. A new approach to array formation uses a parylene overlay cable to connect a 3-D microelectrode array to a custom-designed signal conditioning chip and thence to the external world.

The use of microsystems for many emerging wireless sensing applications has increased the demand for on-site, small-volume, and replacement-free energy sources as opposed to conventional batteries. On-site energy scavenging from various environmental sources including ambient heat, solar energy, and vibration has been introduced as efficient and promising approaches. This work focuses on the use of body heat generated by beetles as an energy source. The goal of this project is to develop a micro thermoelectric generator (TEG) with the area of approximately 1cm2 that is capable of generating 20–50µW/cm2/°C from a beetle’s body heat.

Applying nano-scaled materials and technologies to microsystems has been a primary theme of the research conducted in the WIMS Center since its inception. Nowhere is this more clearly illustrated than in the chemiresistor (CR) arrays we have developed for the WIMS µGC detector. In the latest advancement, we have employed electron-beam lithography to create interdigital electrodes (IDE) with individual Au/Cr fingers and spaces measuring just 300nm in width (~8µm in length).

The Narada wireless sensor platform has been under development at the WIMS Center since 2005. Narada is designed for field deployment in large-scale infrastructure systems where long communication range, power efficiency, and reliability are all necessities. This past summer, the platform was field tested on the Yeondae Bridge, located in Icheon, Korea.