Low-temperature wafer-level transfer bonding

In this paper, we present a new wafer-level transfer bonding technology. The technology can be used to transfer devices or films from one substrate wafer (sacrificial device wafer) to another substrate wafer (target wafer). The transfer bonding technology includes only low-temperature processes; thus, it is compatible with integrated circuits. The process flow consists of low-temperature adhesive bonding followed by sacrificially thinning of the device wafer. The transferred devices/films can be electrically interconnected to the target wafer (e.g., a CMOS wafer) if required. We present three example devices for which we have used the transfer bonding technology. The examples include two polycrystalline silicon structures and a test device for temperature coefficient of resistance measurements of thin-film materials. One of the main advantages of the new transfer bonding technology is that transducers and integrated circuits can be independently processed and optimized on different wafers before integrating the transducers on the integrated circuit wafer. Thus, the transducers can be made of, e.g., monocrystalline silicon or other high-temperature annealed, high-performance materials. Wafer-level transfer bonding can be a competitive alternative to flip-chip bonding, especially for thin-film devices with small feature sizes and when small electrical interconnections (<3×3 μm²) between the devices and the target wafer are required     

Hybrid-mounted micromachined aluminum hotwires for wall shear-stress measurements

In this paper, we present a micromachined metal hotwire anemometer sensor for use in wall shear-stress measurements. We describe its design and fabrication. A novel hybrid assembly method has been developed to make it possible to measure close to the surface without contacting leads interfering with the flow. Experimental results illustrate the behavior and characteristics of this sensor.     

Linear variable optical filter-based ultraviolet microspectrometer

An IC-compatible linear variable optical filter (LVOF) for application in the UV spectral range between 310 and 400 nm has been fabricated using resist reflow and an optimized dry-etching. The LVOF is mounted on the top of a commercially available CMOS camera to result in a UV microspectrometer. A special calibration technique has been employed that is based on an initial spectral measurement on a xenon lamp. The image recorded on the camera during calibration is used in a signal processing algorithm to reconstruct the spectrum of the mercury lamp and the calibration data is subsequently used in UV spectral measurements. Experiments on a fabricated LVOF-based microspectrometer with this calibration approach implemented reveal a spectral resolution of 0.5 nm.     

Micromachined electrodes for biopotential measurements

We describe the microfabrication, packaging and testing of a micromachined dry biopotential electrode, (i.e., where electrolytic gel is not required). It consists of an array of micro-dimensioned, very sharp spikes, (i.e., needles) designed for penetration of human skin which circumvent high impedance problems associated with layers of the outer skin. The spikes are etched in silicon by deep reactive ion etching and are subsequently covered with a silver-silverchloride (Ag-AgCl) double layer. The electrode-skin-electrode impedance of dry spiked electrodes having a size of 4×4 mm² is reduced compared to standard electrodes using electrolytic gel and having a comparable size. Recorded low amplitude biopotentials resulting from the activity of the brain, (i.e., EEG signals) are of high quality, even for spiked electrodes as small as 2×2 mm². The spiked electrode offers a promising alternative to standard electrodes in biomedical applications and is of interest in research of new biomedical methods     

Compatibility assessment of CVD growth of carbon nanofibers on bulk CMOS devices

We compare the level of deterioration in the basic functionality of individual transistors on ASIC chips fabricated in standard 130 nm bulk CMOS technology when subjected to three disparate CVD techniques with relatively low processing temperature to grow carbon nanostructures. We report that the growth technique with the lowest temperature has the least impact on the transistor behavior.     

CMOS considerations in nanoelectromechanical carbon nanotube-based switches

In this paper, we focus on critical issues directly related to the viability of carbon nanotube-based nanoelectromechanical switches, to perform their intended functionality as logic and memory elements, through assessment of typical performance parameters with reference to complementary metal-oxide-semiconductor devices. A detailed analysis of performance metrics regarding threshold voltage control, static and dynamic power dissipation, speed, and integration density is presented. Apart from packaging and reliability issues, these switches seem to be competitive in low power, particularly low-standby power, logic and memory applications.     

Realizing a 140 GHz Gap Waveguide–Based Array Antenna by Low-Cost Injection Molding and Micromachining

This paper presents a novel micromachining process to fabricate a 140 GHz planar antenna based on gap waveguide technology to be used in the next-generation backhauling links. The 140 GHz planar array antenna consists of three layers, all of which have been fabricated using polymer-based microfabrication and injection molding. The 140 GHz antenna has the potential to be used as an element in a bigger 3D array in a line-of-sight (LOS) multiple input multiple output (MIMO) configuration to boost the network capacity. In this work, we focus on the fabrication of a single antenna array element based on gap waveguide technology. Depending on the complexity of each antenna layer’s design, three different micromachining techniques, SU8 fabrication, polydimethylsiloxane (PDMS) molding, and injection molding of the polymer (OSTEMER), together with gold (Au) coating, have been utilized to fabricate a single 140 GHz planar array antenna. The input reflection coefficient was measured to be below???11 dB over a 14% bandwidth from 132 to 152 GHz, and the antenna gain was measured to be 31 dBi at 140 GHz, both of which are in good agreement with the simulations.

     

A silicon resonant sensor structure for Coriolis mass-flowmeasurements

We present the first mass-flow sensor in silicon, based on the Coriolis-force principle. The sensor consists of a double-loop tube resonator structure with a size of only 9×18×1 mm. The tube structure is excited electrostatically into a resonance-bending or torsion vibration mode. A liquid mass flow passing through the tube induces a Coriolis force, resulting in a twisting angular motion phase shifted and perpendicular to the excitation. The excitation and Coriolis-induced angular motion are detected optically. The amplitude of the induced angular motion is linearly proportional to the mass flow and, thus, a measure thereof. The sensor can be used for measurement of fluid density since the resonance frequency of the sensor is a function of the fluid density. The measurements show the device to be a true mass-flow sensor with direction sensitivity and high linearity in the investigated flow range of as low as 0-0.5 g/s in either direction. A sensitivity of 2.95 (mV/V)/(g/s) and standard deviation for the measured values of 0.012 mV/V are demonstrated     

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMA_x-b-AEMA_y/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.     

MEMS Sensor for In Situ TEM Atomic Force Microscopy

Here, we present a MEMS atomic force microscope sensor for use inside a transmission electron microscope (TEM). This enables direct in situ TEM force measurements in the nanonewton range and thus mechanical characterization of nanosized structures. The main design challenges of the system and sensor are to reach a high sensitivity and to make a compact design that allows the sensor to be fitted in the narrow dimensions of the pole gap inside the TEM. In order to miniaturize the sensing device, an integrated detection with piezoresistive elements arranged in a full Wheatstone bridge was used. Fabrication of the sensor was done using standard micromachining techniques, such as ion implantation, oxide growth and deep reactive ion etch. We also present in situ TEM force measurements on nanotubes, which demonstrate the ability to measure spring constants of nanoscale systems.