Niladri Banerjee

Microfluidic device for triggered chip transience

This paper presents the fabrication and testing of a microfluidic device for the triggered destruction (transience) of microchips. The device consists of a thin film array of sealed reservoirs patterned on a polymer film. Each reservoir encloses a corrosive chemical agent which upon release dissolves the surface of a microchip placed beneath. When transience is activated, an integrated micro-heater melts the bottom of the reservoirs thus releasing the chemical agent, which in a matter of minutes destroys key layers on the underlying electronic/sensor chip. Each reservoir consists of a 16 μm-tall cavity holding 1 μL/cm2 of 1000:1 BHF. The measured energy required to burst open a filled reservoir was ~35mJ/cm2 when the device rests on top of a glass substrate and ~100mJ/cm2 when the device rests on top of a 0.5 μm-layer of silicon dioxide on a 0.5 mm silicon wafer.

From chips to dust: The MEMS shatter secure chip

This paper presents the implementation of a transience mechanism for silicon microchips via low-temperature postprocessing steps that transform almost any electronic, optical or MEMS substrate chips into transient ones. Transience is achieved without any hazardous or explosive materials. Triggered chip transience is achieved by the incorporation of a distributed, thermally-activated expanding material on the chip backside. When heated at 160°C the expanding material produces massive chip cleavage mechanically shattering the chip into a heap of silicon dust.

A milli-volt triggered MEMS paddle switch

This paper presents an implementation of an electrostatic MEMS switch which can be triggered by a very low input voltage in the range of ~50mV. This device can thus be used as a zero-DC power signal threshold detector suitable for waking up larger battery powered systems. The device consists of an electrically conductive torsional see-saw paddle with four balanced electrodes. The device is symmetrically biased by applying the same voltage at its inner electrodes leading to bistable behavior at flat or collapsed equilibrium positions. The use of elevated symmetric bias softens the springs such that the transition of the paddle state from flat to collapsed can be triggered when a few mV are applied to one of its outer electrode thus causing device snapping in and switch closure.

Encroachment and line of sight blocking in micro-cavity sealing

This paper investigates the sealing of micro-cavities with line-of-sight blocking (LOSB) barriers. This is a novel concept that mitigates sealant encroachment into the cavity of a sealed MEMS device. The cap layer over the sacrificial layer forms walls around the entry hole that impedes the diffusion of sealant particles and ensures released devices whose operation is unaffected. LPCVD PSG and PECVD SiO2 and Si3N4 have been used as sealant material and relation between etch-hole size and encroachment for cavity thickness ranging in between 1-2 μm have been tested. LOSB walls are highly effective in confining the sealant particles for larger holes and specially Si3N4.

A monolithically integrated multi-sensor platform

The integration of multiple sensors on a single substrate is reported in this paper. A test chip was designed using the integration platform that implemented a capacitive inertial sensor, a capacitive absolute pressure sensor and a capacitive microphone. The sensors were tested after fabrication with the measured acceleration sensitivity of 10fF/g for a full scale acceleration of 2g and the pressure sensor sensitivity of 10fF/KPa for a full scale pressure of 1 atmosphere.

A Monolithically Integrated Multisensor Platform

The integration of multiple sensors on a single substrate is reported in this paper. A test chip was designed using the integration platform that implemented a capacitive inertial sensor, a capacitive absolute pressure sensor, a resistive temperature sensor, and a capacitive microphone. The sensors were tested after fabrication with the measured acceleration sensitivity of 10 fF/g for a full scale acceleration of 2 g and the pressure sensor sensitivity of 10 fF/KPa for a full scale pressure of 1 atm. Temperature sensor and microphone were also electrically tested.

Microballoon pressure sensors for particle imaging manometry in liquid and gaseous media

We present the fabrication and testing of engineered microballoon particles that expand and contract under external pressure changes hence serving as microscopic pressure sensors. The particles consist of 12 μm hollow flexible 0.4 μm-thick parylene-C shells with and without a coating of ultrathin Al2O3 diffusion barriers, and the changes in the particle radius are measured from the particle spectral reflectivity. The microballoons display radial pressure sensitivities of 0.64 nm psi(-1) and 0.44 nm psi(-1), respectively in agreement with theoretical estimates. The microballoon devices were used for mapping the internal pressure drop within microfluidic chips. These devices experience nearly spherical symmetry which could make them potential flow-through sensors for the augmentation of particle-based flow characterization methodologies extending todays capabilities of particle imaging velocimetry.

Fast pulsed heating and impact cooling of thermal microactuators

This paper reports techniques to rapidly heat and cool thermal actuators in microseconds. Rapid temperature changes can lead to high-speed motion and many-fold improvement in load power delivery compared to that achievable with conventional thermal microactuator devices. Rapid heating is achieved by capacitor discharge across the heated element. Rapid cooling is achieved by impacting thin cold plungers that remove heat from hot actuator beams by ultrafast diffusion. We have fabricated and preliminary tested polysilicon thermal actuators based on these principles.

Disposable digital dry powder micro-nebulizer device for drug storage and triggered release

This paper presents the fabrication and testing of a microfabricated dry powder digital nebulizer device for drug storage and triggered release. The device consists of arrays of 40 μm deep sealed cavities of different volumes loaded with solid powder particles on a flexible polymer film. Each discrete cavity contains its own micro-heater triggered release mechanism. Approximately 49 mJ of heater energy is required to release 1.35 μg of powder to a gas stream in less than a second. This disposable and low-cost micro-nebulizer powder storage device has potential for use in inexpensive, long duration storage and controlled release of powder drugs for treatment of cystic fibrosis, asthma and other respiratory diseases.

High-sensitivity parametrically amplified chemo-mechanical vapor sensors

In this paper we present a new kind of high sensitivity chemo-mechanical sensors. These devices consist of a torsional conductive see-saw paddle suspended by two torsional springs from a substrate with symmetric electrodes under each paddle wing. One of the wings is coated with a thin chemically sensitive polymer layer that swells when a specific compound vapor is absorbed. The absorption induced swelling thus causes wing bending and downward deflection proportional to the vapor concentration. Upon application of a fixed DC bias, the deflection is parametrically amplified causing a much larger deflection, and pull-in instability. A sufficiently large amplification results in unstable equilibrium of deflected paddle wing causing it to snap. This amplified drive mechanism does not consume any power, yet it can magnify the observed deflection by one or two orders of magnitude. This deflection is measured through a profilometer as well as a change in capacitance. We present the theory, fabrication and testing results of these sensors.