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Micro & Nanotech : MEMS & NEMS

Micro & Nanotech Portfolios


Simplified Anisotropic Graphene Conductor Emits Terahertz Radiation

UW–Madison researchers have designed an electromagnetic radiation device that can generate THz frequencies using an electrically conducting thin film.

The film is made of graphene layered over a substrate patterned into stripes of two alternating materials, such as germanium and silicon dioxide. This causes the charge carrier mobility across the plane of the thin film to vary periodically. When voltage is applied to the film, electrons flow through, changing velocities and giving rise to a spatially varying electric field. This produces electromagnetic radiation from the exposed surface of the film as the electrons pass through.

The graphene layer can be grown or deposited directly on the patterned substrate using known nanomembrane or thin-sheet transfer techniques.

Ultrasonic Welding with Real-Time Quality Control

UW–Madison researchers and others have developed an ultrasonic welding system that uses thin-film sensors to measure control values, like temperature and heat flux, at the working surface.

The system includes an anvil, welding horn and process controller. The process controller receives measurements taken by the sensors. It then can determine weld quality as the joint is being formed or record the results to help evaluate tool wear.

The thin-film sensors can be commercially available microelectromechanical systems (MEMS) sensors. They may be inserted into slots or attached in the welding device adjacent to the working surface.

Nanoscale Electromagnetic Radiation Device Using Serpentine Conductor

UW-Madison researchers have developed a device for generating electromagnetic radiation by accelerating charges on a small serpentine conductor. This nanoscale device incorporates the strengths of both the FEL and BO methods of electromagnetic radiation generation to provide broadband, tunable radiation sources for portable applications.

The electronic device consists of a first and second electrical terminal and a nanoscale ribbon of conductive material providing a serpentine electrical path between the terminals. When charge carriers (electrons) are accelerated in the exposed curve portions of the ribbon, acceleration-induced electromagnetic radiation is emitted. The small dimensions of the ribbon constrain the charge carriers to a series of small-radius curves capable of producing electromagnetic radiation in the microwave range and potentially at light frequencies. The addition of resonant-cavity structures and/or optically active layers produces stimulated emission of coherent, laser-like radiation from a small device. Tuning of the radiation frequencies is possible by physically altering the dimensions of the structure or changing the electrical potential driving the charge carriers.

Antenna-Based Power Generation with Nanoscale Rectifying Elements


High-Frequency Bridge Suspended Diode for Power Generation from High Frequency Microwave Sources

UW-Madison researchers have developed full metal electrical nano-diodes and a method to fabricate such diodes with desirable properties for high-frequency applications. The diodes produced by this method have an ultra-high cutoff frequency, since most of the surrounding dielectric material is removed. The method involves a metal-coated semiconductor structure, which is further coated with a Teflon-like layer. The semiconductor substrate material is then etched, leaving islands of metal suspended by the Teflon-like material. The suspended islands operate as coupled MIM junctions. This structure functions as a freely suspended diode with reduced parasitic junction capacitance.

Efficient and Automated Analysis of Thin Structures to Enhance Engineering 3-D Modeling Software

UW-Madison researchers have developed a new technology for a fully automated and efficient analysis of thin structures.  The new process overcomes the limitations of conventional geometric reduction and 3-D FEA by providing a dual-representation, in which the geometry is captured in 3-D, but the physics of the structure are captured via classic beam, plate or shell theory. 

The integration of 3-D geometry and lower-dimensional physics leads to numerous advantages:
  1. The technology can be directly integrated into 3-D CAD systems.
  2. The 3-D CAD model need not be simplified or dimensionally reduced prior to analysis.
  3. A boundary triangulation of the CAD model is sufficient for analysis, i.e., a 3-D mesh is not required.
  4. It retains the ability to achieve the accuracy of modern lower-dimensional beam, plate and shell methods.
This process is particularly well-suited for analyzing thin structures since it offers the flexibility and generality of 3-D FEA and the computational efficiency and accuracy of beam, plate or shell analysis.  The new method and system will streamline 3-D structural analysis in many fields of engineering design because this process can be incorporated into traditional CAD software via conventional integration techniques. 

Nanoelectromechanical Switch in Co-Planar Waveguide

UW-Madison researchers have developed a co-planar waveguide that uses a NEMSET electromechanical signal switch for signal modulation. The NEMSET switch acts as a natural communication pathway between co-planar elements of co-planar waveguides. The device operates in the frequency range of 1MHz to 2GHz to filter, modulate, mix and rectify microwave signals. This waveguide could be used in the same way as a traditional waveguide in electrical engineering, but with the benefits of NEMSET and a co-planar structure.

Smart Leaf Technology - Floating Semiconductor Membranes for Wireless Sensing

UW-Madison researchers have developed wireless sensors made from nanoscale membranes for use in detecting the presence or absence of analytes, systems incorporating the sensors and methods for using the sensors. The “smart leaf” sensors are made of two thin films with opposing front and back surfaces. The surfaces are coated with molecules that react with the target analyte. Upon exposure to the analyte, the molecules alter the geometry of the leaf and change its dielectric response in a manner that depends on the concentration of the target chemical. An electromagnetic source continually exposes an array of sensors to an electromagnetic signal, while a detector regularly scans the sensor array to observe any change in the reflected and/or transmitted radiation. In this way, the presence or even the concentration of a particular analyte may be easily detected without requiring the sensors to be directly wired to a power supply.

Nano-Mechanical Computer Based on Nano-Electro-Mechanical Transistors

UW-Madison researchers have developed a robust alternative to conventional transistors: a nano-electro-mechanical transistor based on the nano-electro-mechanical single electron transistor (NEMSET). These nanoscale switching elements may be interconnected in the same way as conventional circuits to create a nano-mechanical computer with the benefits of NEMSET. However, they offer the benefit of being immune to radiation disruption, and the design holds promise for extremely low power dissipation. They can be readily constructed using standard integrated circuit techniques, and can operate at temperatures far exceeding conventional transistors (up to 500ºC).

Nano-mechanical computers have operating speeds on the order of 1 GHz. While this speed is not competitive with traditional CMOS technology, it is sufficient for applications like cell phones, calculators and other micro-controllers, which require robust and low power consumption.

Microscope Probe Having an Ultra-Tall Tip

UW-Madison researchers have developed a method for fabricating a microscopic coaxial tip with a height greater than 30 micrometers. A coaxial tip and a coplanar waveguide are formed on a silicon substrate. The first layer of the tip shaft is made of a conductive material. Over the first layer, a layer of non-conducting material is deposited, followed by a layer of a different conducting material. An oxide etch exposes the first conductive layer at the tip.

Metal-Coated Vertically Aligned Carbon Nanofibers

UW-Madison researchers have developed a method for decorating carbon nanostructures with uniform metal coatings to provide electrodes with high structural stability and surface area. The process uses arrays of vertically aligned carbon nanofibers separated by interstices. The nanofibers are functionalized by covalently binding a layer of organic linker molecules to their surface. Electroless deposition is then used to deposit a continuous metal coating onto the functionalized surfaces. The resulting metal-coated nanofibers form highly stable and reproducible electrodes with high surface areas. These electrodes can be used in devices such as supercapacitors and fuel cells.

Microelectronics Grade Metal Substrate and Related Metal-Embedded Devices

UW-Madison researchers have developed a novel method of creating a microelectronics-grade metal substrate with embedded sensors or other microelectronic devices. The metal substrate is formed on a sacrificial silicon substrate. An adhesion layer is deposited on the sacrificial substrate, followed by a seed layer of the metal. The metal material is then deposited on the seed layer via a low-temperature, low-stress process, such as electroplating, to form a microelectronics-grade substrate. Thin film sensors and/or other microelectronic devices, followed by the appropriate insulating layer(s), may be fabricated on the sacrificial substrate before the metal substrate is formed. The sacrificial silicon substrate is then etched away, leaving the microelectronics-grade metal substrate and possibly the microelectronics device. Finally, an insulating layer(s), followed by an adhesion layer, a seed layer, and additional amounts of the metal substrate, are deposited over the now exposed microelectronics device to encapsulate it within a metal shell. The encapsulated sensor and microelectronics-grade metal substrate are then ready to be embedded in high-melting temperature bulk material.

Self-Regulating Microsystem that Integrates Silicon- and Polymer-Based MEMS Platforms

UW-Madison researchers have developed an approach to fabricating microsystems that leverages the strengths of both silicon- and polymer-based MEMS platforms. Specifically, they have constructed and tested a self-regulating, temperature-controlled micromixer for creating flow within microchannels.

As in other MEMS, an externally-applied rotating magnetic field drives the mixer’s rotation. But unlike traditional MEMS, which employ standard actuators, the micromixer is turned off and on by using temperature-sensitive hydrogel polymers. 

When the fluid temperature inside a MEMS device rises above a certain temperature, a temperature-sensitive hydrogel ring surrounding the mixer’s axel contracts, freeing the mixer to rotate under control of the magnetic field and pump fluid through the device to cool it. When the temperature cools sufficiently, the hydrogel ring expands and halts the mixer’s rotation.

Method to Protect NEMS Structures During Manufacturing to Greatly Increase Device Yields

UW-Madison researchers have developed a method to protect nanoelectromechanical systems during wet etching, resulting in much higher yield of usable devices from the manufacturing process. The method involves depositing a carbon layer of diamond-like hardness (i.e., a protective mask) over the NEMS structure. The mask is deposited by electron beam deposition (EBD) using residual carbon atoms in the vacuum chamber. After the main processing steps, including wet etching, the carbon/mask layer is removed using plasma etching to reveal the usable NEMS structure.

Micromechanical Actuator Device

UW-Madison researchers have developed a micromechanical, electrothermal actuator device that can provide rectilinear displacements of 100 microns or more. The device employs structures, called compliant mechanisms or flexures, which deform elastically to transmit force or displacement. When a mesh of compliant structures (called a compliant microtransmission) is coupled to an electrothermal actuator in this device, it amplifies the motion of the actuator to produce displacements 10 to 20 times greater than the actuator alone could provide.

Direct Charge Radioisotope Activation and Power Generation for Microelectromechanical Systems

UW-Madison researchers have developed an electrical power generator that has several advantages over conventional power sources for microsystems. Specifically, the energy carried by particles emitted by radioactive decay is captured and converted to mechanical potential energy that is stored in an elastically deformable element. The energy can be used to activate other mechanical parts directly or can be converted to electrical energy.

Method and Apparatus for Carbon Nanotube Production

A UW-Madison researcher has developed a method for driving the cathode ultrasonically, resulting in a high tip acceleration that dislodges large carbon chunks, leaving the lighter nanotubes to form. The method also describes the use of a cooling method on the cathode to diminish the formation of unwanted carbon material. Nanotubes created using this technique are greatly increased in length (greater than one mm) and quantity.

Improved Method for Releasing Micromechanical Structures

UW–Madison researchers have developed a method of freeing a micromachined part from the surface of a substrate to which the micropart is stiction bonded. An external piezoelectric force is applied to the bottom surface of the substrate, sending a pulse stress wave through the substrate, which propagates from the bottom surface and reflects over the top surface. The reflection of the wave causes a rapid up and down displacement of the surface, which breaks the bond between the micropart and the substrate surface. This method also can be used to displace a micropart that is in contact with a substrate top surface, but not bonded to it.