The field of cantilever-based sensing emerged in the mid-1990s and is today a well-known technology for label-free sensing which holds promise as a technique for cheap, portable, sensitive and highly parallel analysis systems. The research in sensor realization as well as sensor applications has increased significantly over the past 10 years. In this review we will present the basic modes of operation in cantilever-like micromechanical sensors and discuss optical and electrical means for signal transduction. The fundamental processes for realizing miniaturized cantilevers are described with focus on silicon- and polymer-based technologies. Examples of recent sensor applications are given covering such diverse fields as drug discovery, food diagnostics, material characterizations and explosives detection.

http://iopscience.iop.org/article/10.1088/0034-4885/74/3/036101/pdf

Cantilever-like micromechanical sensors

Lab-on-a-chip devices

In this Review, the interplay between materials and microfluidics is examined, with the discussion focused on how recent advances in materials fabrication have expanded the frontiers of microfluidic platforms and how the new microfluidic capabilities are, in turn, furthering materials design.

Interplay between materials and microfluidics

We report the successful fabrication and testing of 3D printed microfluidic devices with integrated membrane-based valves. Fabrication is performed with a low-cost commercially available stereolithographic 3D printer. Horizontal microfluidic channels with designed rectangular cross sectional dimensions as small as 350 μm wide and 250 μm tall are printed with 100% yield, as are cylindrical vertical microfluidic channels with 350 μm designed (210 μm actual) diameters. Based on our previous work [Rogers et al., Anal. Chem. 83, 6418 (2011)], we use a custom resin formulation tailored for low non-specific protein adsorption. Valves are fabricated with a membrane consisting of a single build layer. The fluid pressure required to open a closed valve is the same as the control pressure holding the valve closed. 3D printed valves are successfully demonstrated for up to 800 actuations.

/pdf/3d-printed-microfluidic-devices-with-integrated-valves-3uvp3g9m5s.pdf

3D printed microfluidic devices with integrated valves

Casimir effect on the critical pull-in gap and pull-in voltage of nanoelectromechanical switches is studied. An approximate analytical expression of the critical pull-in gap with Casimir force is presented by the perturbation theory. The corresponding pull-in parameters are computed numerically, from which one can notice the nonlinear effect of Casimir force on the pull-in parameters. The detachment length has been presented, which increases with increasing thickness of the beam.

Casimir effect on the pull-in parameters of nanometer switches. Microsys Technol

Poly(dimethylglutarimide) (PMGI) is a resist that is commonly used in bilayer and trilayer imaging applications. PMGI can be exposed using various radiation sources including deep UV. Currently, there are only two developers for PMGI reported in the literature: tetramethylammonium hydroxide and tetraethylammonium hydroxide. We introduce a new developer for PMGI, a mixture of isopropanol (IPA) and water. Samples were irradiated with deep UV at 254 nm. The IPA/water developer exhibits rapid dissolution of exposed PMGI, of many microns per minute. However, PMGI exhibits high absorption at 254 nm, so the development depth is limited. The depth limit, after a critical dose, increases linearly with the exposure dose.

Isopropanol/water as a developer for poly(dimethylglutarimide)

Often microsystems require switches or mechanisms that can give two stable states. Currently, many micromechanical systems use a monostable switch to produce the two states: a first stable state when no power is applied and a second state that requires constant power to maintain the stability. Such a configuration is not efficient and consumes considerable electrical power during the 'on' state of the switch. A more efficient design would be a device that consumes energy only during the switching operation and does not consume any power while holding the stable states. Our novel micromechanical bistable switch design is based on the locking mechanism of an extension ladder. This switch was designed and fabricated through multi-user MEMS processes (MUMPs). Our paper outlines the design, simulation, animation and results from the testing of the micro-fabricated system. Actual performance of the switch was videographically analyzed and compared with theory and simulation.

A surface micromachined bistable switch

Micro-electro-mechanical-systems (MEMS) have designs which incorporate freestanding structures. These freestanding structures must be attached to the substrate during fabrication, and released when they are to be utilized. Tethers are long thin beams that mechanically anchor the freestanding structure to the substrate. In our study, we focused on the fuse-tether design and its associated Joule heating breaking technique. We investigated the breaking characteristics of two fuse-tether designs based on different current pulses. For each design, the current pulse which produced the most desirable break was chosen for more rigorous testing on 20 tethers. The reliability tests resulted in at least 80% success rate. In addition to empirical testing, we utilized ANSYStrade to simulate the Joule heating process. The ANSYStrade model produced results that closely matched the break characteristics observed in the empirical tests. This research demonstrated that a fuse-tether can be severed reliably with the Joule heating technique, and the outcome can be predicted with proper modeling before fabrication

Fuse-tethers in MEMS: theory and operation

We are currently developing basic building blocks for creating digital logic units that are based on mechanical components. Transistors, which are semiconductor devices, rely on doping to change intrinsic semiconductor to extrinsic semiconductors. However, at low or high temperatures, that control is impossible as semiconductors revert to intrinsic behaviour. Also, semiconductors exhibit various complications under ionizing (radiation) environment. 
We have fabricated logic units using micro-mechanical relays using MEMS technology. The logic units consist of a micro-mechanical relay with three electrical gates. The mechanical relay is fabricated with a cantilever over an airgap, and is operated by applying voltage to the gate. The applied voltage creates an electric force between the gate and a cantilever structure. The electrostatic force arches the cantilever into electrical contact. Since the operation does not depend on controlling the type of charge carriers, the proposed method does not suffer from the limitations shared by semiconductors. With different input combinations applied to the gates of the device, development of MEMS mechanical logic, leading to general digital circuits, is possible. Characterization of the devices is performed, which includes operation times, operation voltages, and maximum 
currents. Design, fabrication and testing of these micro-mechanical logic elements will be presented in the paper.

MEMS mechanical logic units: characterization and improvements of devices fabricated with MicraGEM and PolyMUMPs

This paper describes a pulse width modulation controlled bistable microelectromechanical system (MEMS). A bistable mechanism offers two distinct equilibrium states without requiring input power to stay in either of the stable states. The state of the single digital input bistable MEMS device described in this paper is determined by the duration of the input pulse to the actuators. Applications of bistable mechanisms include MEMS relays and optical switches. By using a single digital input and pulse width modulation control, this design allows for easier integration with digital drive circuitry. This mechanism is able to use a single digital input because it utilizes the difference in time constants between two perpendicular actuators. The design consists of two actuators situated perpendicularly to each other, which are both connected to a hook shape. This hook latches with an opposing hook, which anchored to the substrate, when an input pulse of sufficient duration is applied to the actuators. The hooks will disengage when an input pulse of appropriate duration is applied to the actuators. Operating principles and physical theory behind the actuation technique is discussed in detail. As well, the current state of this research and an analysis of a prototype device fabricated using MUMPsreg are discussed

R.W. Johnstone

Papers

Isopropanol/water as a developer for poly(dimethylglutarimide)

A surface micromachined bistable switch

Fuse-tethers in MEMS: theory and operation

MEMS mechanical logic units: characterization and improvements of devices fabricated with MicraGEM and PolyMUMPs

A pulse width modulation controlled bistable microelectromechanical system