AVS2010 Session MN-ThP: MEMS and NEMS Poster Session

There is considerable research at present on the performance and properties of nanosheets, nanofibers and other functional nanomaterials such as fullerenes and nanotubes. This is particularly true of carbon nanotube, made from carbon atoms, where many research projects throughout the world are looking at measurement techniques for evaluating electrical and electronic characteristics with a view to developing electronic device applications such as high-intensity field-emitted electron sources and ultra-fast transistors. We have prepared long crystal silicon wires with a diameter of several tens of nano meters at a temperature lower than 523k by using the low-pressure low-temperature CVD method. To use these as materials for application to micro-nano electromechanical system, we need to fully understand their electric, chemical and mechanical properties. However, we have not yet to see a genuine, flexible methodology for evaluating the key characteristic of mechanical strength essential to micro-nano structural materials development the nanoscale equivalent of mechanical strength testers for ordinary materials. This is due to the inherent difficulties associated with the manipulation and transportation of materials at the micro-nano scale level.The most difficult part of the handling of small materials is to fix material samples.

The boundary condition at the liquid-solid interface in micro/nano scale is an important issue in micro/nanofluidics systems. Recent studies have shown that the fluid velocity near solid surfaces is not equal to the velocity of the solid surface on hydrophobic surfaces, which is called boundary slip. The degree of boundary slip is evaluated by a slip length. Theoretical and experimental studies suggest that at the solid-liquid interface, the presence of nanobubbles is responsible for the breakdown of the no-slip condition. Nanobubbles are long lasting on hydrophobic surfaces, and movement and coalescence of nanobubbles are observed with higher scan loads during imaging with tapping mode AFM.

In this study, both contact and dynamic AFM methods have been applied to study the boundary slip on hydrophilic, hydrophobic, and superhydrophobic surfaces. An AFM based technique is developed to study boundary slip. Nanobubble movement and coalescence, as well as tip-bubble interaction, are studied in detail. The physical interaction between nanobubbles and the surfaces supporting them is investigated.

This paper presents the development of high-density cylindrical ion trap array for mass spectrometer (CIT-MS).The previous research has mainly focused on the adjusting the ring electrode radius r₀, cylinder length z₀, and endplate hole electrode r_H (Figure 1) and developing a fabrication process involving a back-to-back bonding of two half CIT structures. However, recently it has been noticed that a key factor that limits the performance of the CIT is the high capacitance between endplate electrodes and ring electrode due to the small gap; besides, the back-to-back bonding of two half structures could bring a maximum 5 micron misalignment. Based on these concerns, a new geometry of CIT array for mass spectrometer has been designed; also a new fabrication process has been developed accordingly.

In the newly developed generation of CIT-MS, the geometry design of CIT has been focusing on increasing the gap between the ring electrode and endplate electrode. Several simulations have been done on this subject. Other important improvements include better ring-to-endplate aperture alignment using dedicated alignment marks during flip-chip bonding, hexagonal orientation of traps leading to smaller pitch between each trap to increase density (thereby more trapping volume per unit area of wafer), larger vacuum gaps for operation at higher voltages for increased mass range and selective metallization using lithography techniques to reduce the overlap area of ring and endplate electrodes for lower capacitance.

A new fabrication process has been designed to achieve the improvements mentioned above. A suspended endplate electrode structure, using KOH/DRIE etching techniques, was used to increase the gap and reduce the overlapping area at the same time. To avoid surface charging of the dielectric surface that is exposed to ions, Atomic Layer Deposition (ALD) was investigated to deposit highly resistive (ZnO) layer on the dielectric surface to dissipate charge, while adding minimum to the capacitance. Flip-chip bonding was used to bond the ring-electrode and endplate electrodes and minimize the misalignment between the two substrates. With these considerations, both the esolution specificity and sensitivity are expected to improve. The design of optical mask for this process is underway and we report preliminary progress based on the latest findings.

We present preliminary results using computer simulation of chemical vapor deposition into vertically aligned carbon nanotube (VACNT) forests. The model is based upon deposition processes used in the carbon nanotube templated microfabrication (CNT-M) process. It utilizes VACNT arrays as a framework into which matter is infiltrated via a chemical vapor deposition (CVD)-type process to create solid microstructures and microelectromechanical systems (MEMS). These can have large aspect ratios (200:1) and startling heights (to date up to a mm). Long nozzles with narrow ID and other structures have been made that would be difficult by subtractive techniques. One of the biggest advantages of CNT-M is the promise of being able to prepare MEMS from any desired solid material that can be deposited by CVD, though to date this has only been amorphous and polycrystalline Si, SiO2, SiC, silicon nitride and amorphous carbon.

This work was inspired by the desire to understand how the gas diffusion, reaction and nucleation and growth models used to describe, mostly 2-D, thin-film CVD can be applied to understanding growth on the individual carbon nanotubes and nanotube bundles that make up a VACNT structure. This scaffolding is 3-dimensional, but “rarified”- that is > 99% empty and geometrically complex, and is vital for use of the CNT-M process. How it changes from mostly emptiness to a filled structure was a puzzle. Without optimized growth parameters, deposition is limited to the exterior of the VACNT forests and the structural integrity of the MEMS is poor. In addition, the adhesion of the MEMS devices to the substrate is often inadequate, which leads to low yields and frequent device failure.

Our model explores how the deposition rate, VACNT geometry, and VACNT forest density affects the filling of the forest. We base the parameters in our model on data from the TEM analysis of MEMS devices fabricated using the CNT-M process with CVD-deposited polysilicon, amorphous carbon, and silicon nitride.