Functional nano-structuring of thin silicon nitride membranes

The paper describes the development and production of a nano-optical device consisting of a nano-perforated layer of silicon nitride stretched in a single-crystal silicon frame using electron beam lithography (EBL) and reactive ion etching (RIE) techniques. Procedures for transferring nanostructures to the nitride layer are described, starting with the preparation of a metallic mask layer by physical vapor deposition (PVD), high-resolution pattern recording technique using EBL and the transfer of the motif into the functional layer using the RIE technique. Theoretical aspects are summarized including technological issues, achieved results and application potential of patterned silicon nitride membranes.

Geometrical and electronic properties of PdWSin (n=10–20) semiconductor materials

Geometries and electronic properties of PdWSin (n=10–20) clusters are investigated by density functional methods. According to our calculated results, it is obvious that tungsten (W)-encapsulated silicon frame determines the final PdWSin (n=10–20) forms because W and silicon (Si) interactions are stronger than palladium (Pd)-Si interactions. The electronic charges are transferred from the Si frame to W firstly and Pd finally, which is completely different from the homoatomic transition metal (TM)2-doped silicon clusters. The calculated highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps exhibit that PdWSi12 has the biggest HOMO-LUMO gap.

A MEMS Magnetometer Utilizing a NdFeB Magnet

A silicon MEMS magnetometer has been developed that utilizes a miniature NdFeB rare earth magnet attached to a silicon platform that is suspended by a dual torsional suspension system. An externally applied out-of-plane magnetic field will cause a magnetic torque to be produced between the external field and the NdFeB magnet, causing a deflection of the suspended silicon platform which can be sensed capacitively. The device measures 5.6 mm X 5.6 mm, with the silicon components being manufactured using bulk micromachining processes. The variable capacitive structure is realized by metalizing the bottom side of the suspended silicon platform to allow the silicon platform to serve as the top electrode. The bottom electrode is provided by a bare pad on a printed circuit board (PCB) to which the frame of the silicon device is attached. This results in a variable capacitance with a nominal value of approximately 3–6 pF, depending on the exact width of the gap. The variable capacitance is large enough to be converted into a variable frequency square wave using a CMOS relaxation oscillator circuit. To realize a practical device, multiple silicon components were manufactured. First, a silicon component had to be manufactured that included the anchor/frame, torsional springs, and suspended platform. To provide protection against destructive over-ranging of the mechanical components during very high accelerations or external magnetic fields, another silicon component was manufactured that provided mechanical stops at the limits of the useful displacement range. Two other components were also manufactured on the same wafer to provide for a cap over the device. Epoxy was used to bond the NdFeB magnet and the various silicon components together. The fabricated devices behaved similarly to their predicted theoretical performance, with a nominal oscillation frequency around 30 kHz, a sensitivity around 100 nT/Hz, and a noise floor around 50 nT. Several fabrication and assembly issues had to be solved in order to realize the device. The gap width of the capacitive structure is dependent on the thickness of the agent used to electrically connect the silicon anchor to a pad on a PCB. As it is desirable to minimize this gap width, some experimentation was required to find a suitable agent and assembly method. Additionally, the bonding agent used to attach the silicon anchor to the PCB must be applied at a temperature near the expected operating temperature of the device to prevent large stresses from being applied to the silicon frame due to the difference in the coefficients of thermal expansion between silicon and FR4. Also, during fabrication it was found that large flat areas, where a very uniform etch is critical, required wet KOH etching, while deep reactive ion etching could be used for areas where depth and a high aspect ratio were important. Significance This MEMS sensor represents a novel configuration for sensing magnetic fields. Without much optimization, the sensor already exceeds the sensitivity of many commercially available Hall-effect based MEMS magnetometers. As MEMS magnetometers are less developed than alternative magnetometer technologies, they may have more opportunities for improvement.

Fabrication of Hybrid Diamond and Transparent Conducting Metal Oxide Electrode for Spectroelectrochemistry

A novel diamond transparent electrode is constructed by integrating conductive diamond film and transparent conducting metal oxide to combine the superior electrochemical properties of diamond and the electrical conductivity of transparent metal oxide (TCO). Direct growth of diamond on indium tin oxide (ITO) and aluminium doped zinc oxide (AZO) was explored, but X-ray photoelectron spectroscopy measurement reveals that both substrates cannot survive from the aggressive environment of diamond growth even if the latter is regarded as one of the most stable TCO. As a second route, a diamond membrane in silicon frame was prepared by selective chemical etching, and a diamond optically transparent electrode (OTE) was constructed by assembling the diamond membrane on the top of an ITO-coated substrate. The resulting device exhibits a high optical transparency and quasireversible electrochemical kinetics, which are competitive to other diamond OTEs reported previously. Its application in UV-Vis spectroelectrochemical studies on the oxidisation of 4-aminophenol was demonstrated.

Development of a Novel Micro-Gripper Integrating Tri-Axial Force Sensor

A novel micro gripper integrating tri-axial force sensor and two grades displacement amplifier is presented in this paper, which bases on the technology of Piezoresistive detection and use PZT as its micro driving component. The micro tri-axial force sensor is fabricated on a single-crystalline-silicon by the technology of MEMS and consists of a flexible cross-structure realized by deep reactive ion etching (DRIE). The arms of the cross-structure are connected to a silicon frame and to the central part of the cross-structure. After modeling the amplifier structure of micro gripper and the sensor, finite element method (FEM) is used to analyze the displacement of the micro gripper and the deformation of the cross-structure elastic cantilever. A calibration method of tri-axial sensor based on the technology of microscopic vision and the principle of bending deflection cantilever is proposed. The experimental verified that the sensor are high level of intrinsic decoupling of the signals from strain gauge, high resolutions in all three axes, high linearity and repeatability and simple produce of calculation. And also show the micro gripper is reasonable and practical. The sensor is capable of resolving forces up to 10mN with resolution of 2.4μN in x axis and y axis and up to 10mN with resolution of 4.2μN in z axis; the gripping displacement of the micro gripper is from 20μm to 300μm.

Low Temperature Eutectic Bonding for In-Plane Type Micro Thermoelectric Cooler

We report the fabrication of a micro thermoelectric (TE) cooler (μ-TEC), lithographically patterned and integrated with silicon micromachining technologies, with an emphasis on two low temperature eutectic bonding techniques used to connect p- and n-type TE microbeams. The result is a microscale cooling spot suspended only by microbridges made purely of TE material at the center of a silicon frame. With no additional material in contact with the cooling spot, thermal leakage is minimized — the critical requirement in making effective μ-TEC’s. Since TE materials degrade at high temperature (> 400°C), connections of p-n microbeams are limited to only low temperature (∼250°C) bonding methods. The overall fabrication procedure has been designed such that most TE thin films can be used without the need to redesign the remaining process flow of the device as TE materials research continues to advance.

Tensile Behavior of Free-Standing Gold Films

ABSTRACTA method for tensile testing thin gold films is presented. Free-standing tensile specimens were prepared by evaporating 0.8 μm of gold onto a patterned oxidized silicon wafer. Using common microelectronic fabrication techniques, free-standing thin film specimens were produced that span rectangular windows in the wafer. The wafer was diced into individual tensile specimens composed of a thin film surrounded by a silicon frame. The final step before testing was to cleave the silicon frame so that the load was completely carried by the metal film. The ultimate tensile strength of the films was found to be approximately 150% greater than that of annealed bulk gold. In contrast, the measured elastic modulus for the thin film specimens was approximately the same as that documented for bulk gold.

A new method for measuring the strength and ductility of thin films

A new method of measuring the mechanical strength of thin films is described. We prepare miniature arrays of four tensile specimens, each 0.25 mm wide, 1 mm long, and 2.2 μm thick, using deposition, patterning, and etching processes common to the semiconductor industry. Each array of four specimens is carried on and protected by a rectangular silicon frame. Thirty-six such specimens are produced on a single wafer. After a specimen frame is mounted, its vertical sides are severed without damaging the specimens. The load is applied by micrometers through a special tension spring. Tensile properties of a 2.2 μm thick Ti–Al–Ti film were determined.