Thermal Boundary Conductance of Direct Bonded Aluminum Nitride to Silicon Interfaces.

Heat accumulation and self-heating have become key issues in microelectronics owing to the ever-decreasing size of components and the move toward three-dimensional structures. A significant challenge for solving these issues is thermally isolating materials, such as silicon dioxide (SiO2), which are commonly used in microelectronics. The silicon-on-insulator (SOI) structure is a great demonstrator of the limitations of SiO2 as the low thermal conductivity insulator prevents heat dissipation through the bottom of a device built on a SOI wafer. Replacing SiO2 with a more thermally conductive material could yield immediate results for improved heat dissipation of SOI structures. However, the introduction of alternate materials creates unknown interfaces, which can have a large impact on the overall thermal conductivity of the structure. In this work, we studied a direct bonded AlN-to-SOI wafer (AlN-SOI) by measuring the thermal conductivity of AlN and the thermal boundary conductance (TBC) of silicon (Si)/AlN and Si/SiO2/aluminum-oxygen-nitrogen (AlON)/AlN interfaces, the latter of which were formed during plasma-activated bonding. The results show that the AlN-SOI possesses superior thermal properties to those of a traditional SOI wafer, with the thermal conductivity of AlN measured at roughly 40 W m-1 K-1 and the TBC of both interfaces at roughly 100 MW m-2 K-1. These results show that AlN-SOI is a very promising structure for improving heat dissipation in future microelectronics.

Detection of In-Plane Movement in Electrically Actuated Microelectromechanical Systems Using a Scanning Electron Microscope.

The measurement of in-plane motion in microelectromechanical systems (MEMS) is a challenge for existing measurement techniques due to the small size of the moving devices and the low amplitude of motion. This paper studied the possibility of using images obtained using a scanning electron microscope (SEM) together with existing motion detection algorithms to characterize the motion of MEMS. SEM imaging has previously been used to detect motion in MEMS device. However, the differences in how SEM imaging and optical imaging capture motion, together with possible interference caused by electrical actuation, create doubts about how accurately motion could be detected in a SEM. In this work, it is shown that existing motion detection algorithms can be used to detect movement with an amplitude of 69 nm. In addition, the properties of SEM images, such as bright edges, complement these algorithms. Electrical actuation was found to cause error in the measurement, however, the error was limited to regions that were electrically connected to the actuating probes and minimal error could be detected in regions that were electrically insulated from the probes. These results show that an SEM is a powerful tool for characterizing low amplitude motion and electrical contacts in MEMS and allow for the detection of motion under 100 nm in amplitude.

Aluminum Nitride to Silicon Direct Bonding for an Alternative Silicon-On-Insulator Platform.

The next generation of microelectromechanical systems (MEMS) requires new materials and platforms that can exploit the intrinsic properties of advanced materials and structures, such as materials with high thermal conductivity, broad optical transmission spectra, piezoelectric properties, and miniaturization potential. Therefore, we need to look beyond standard SiO2-based silicon-on-insulator (SOI) structures to realize ubiquitous MEMS. This work proposes using AlN as an alternative SOI structure due to several inherent material property advantages as well as functional advantages. This work presents the results of reactively sputtered AlN films on a Si handle wafer bonded with a mirror-polished Si device wafer. Wafer bonding was achieved by using hydrophilic wafer bonding processes, which was realized by appropriate polymerization of the prebonding surfaces. Plasma activation of the AlN surface included O2, Ar, SF6, SF6 + Ar, and/or SF6 + O2, which resulted in a change in the chemical and topography state of the surface. Changes in the AlN surface properties included enhanced hydrophilicity, reduced surface roughness, and low nanotopography, components essential for successful hydrophilic direct wafer bonding. Wafer bonding experiments were carried out using promising surface activation methods. The results showed a multilayered bonding interface of Si(Device)/SiO2/ALON/AlN/Si(Handle) with fluorine in the aluminum oxynitride layer from the proceeding AlN surface activation process. More notably, this work provided wafer bonding tensile strength results of the AlN alternative SOI structure that compares with the traditional SiO2 SOI counterpart, making AlN to Si direct bonding an attractive alternative SOI platform.

Chemically Stable Atomic-Layer-Deposited Al2O3 Films for Processability.

Atomic-layer-deposited alumina (ALD Al2O3) can be utilized for passivation, structural, and functional purposes in electronics. In all cases, the deposited film is usually expected to maintain chemical stability over the lifetime of the device or during processing. However, as-deposited ALD Al2O3 is typically amorphous with poor resistance to chemical attack by aggressive solutions employed in electronics manufacturing. Therefore, such films may not be suitable for further processing as solvent treatments could weaken the protective barrier properties of the film or dissolved material could contaminate the solvent baths, which can cause cross-contamination of a production line used to manufacture different products. On the contrary, heat-treated, crystalline ALD Al2O3 has shown resistance to deterioration in solutions, such as standard clean (SC) 1 and 2. In this study, ALD Al2O3 was deposited from four different precursor combinations and subsequently annealed either at 600, 800, or 1000 °C for 1 h. Crystalline Al2O3 was achieved after the 800 and 1000 °C heat treatments. The crystalline films showed apparent stability in SC-1 and HF solutions. However, ellipsometry and electron microscopy showed that a prolonged exposure (60 min) to SC-1 and HF had induced a decrease in the refractive index and nanocracks in the films annealed at 800 °C. The degradation mechanism of the unstable crystalline film and the microstructure of the film, fully stable in SC-1 and with minor reaction with HF, were studied with transmission electron microscopy. Although both crystallized films had the same alumina transition phase, the film annealed at 800 °C in N2, with a less developed microstructure such as embedded amorphous regions and an uneven interfacial reaction layer, deteriorates at the amorphous regions and at the substrate-film interface. On the contrary, the stable film annealed at 1000 °C in N2 had considerably less embedded amorphous regions and a uniform Al-O-Si interfacial layer.

Choice of osteoblast model critical for studying the effects of electromagnetic stimulation on osteogenesis in vitro.

The clinical benefits of electromagnetic field (EMF) therapy in enhancing osteogenesis have been acknowledged for decades, but agreement regarding the underlying mechanisms continues to be sought. Studies have shown EMFs to promote osteoblast-like cell proliferation, or contrarily, to induce differentiation and enhance mineralization. Typically these disparities have been attributed to methodological differences. The present paper argues the possibility that the chosen osteoblast model impacts stimulation outcome. Phenotypically immature cells, particularly at low seeding densities, appear to be prone to EMF-amplified proliferation. Conversely, mature cells at higher densities seem to be predisposed to earlier onset differentiation and mineralization. This suggests that EMFs augment ongoing processes in cell populations. To test this hypothesis, mature SaOS-2 cells and immature MC3T3-E1 cells at various densities, with or without osteo-induction, were exposed to sinusoidal 50 Hz EMF. The exposure stimulated the proliferation of MC3T3-E1 and inhibited the proliferation of SaOS-2 cells. Baseline alkaline phosphatase (ALP) expression of SaOS-2 cells was high and rapidly further increased with EMF exposure, whereas ALP effects in MC3T3-E1 cells were not seen until the second week. Thus both cell types responded differently to EMF stimulation, corroborating the hypothesis that the phenotypic maturity and culture stage of cells influence stimulation outcome.

Improving the function of dopamine electrodes with novel carbon materials.

For therapeutic purposes, an accurate measurement of dopamine level in situ would be highly desirable. A novel strategy for the selective determination of dopamine concentration based on the diamond-like carbon (DLC) electrode is presented in this abstract. The developed DLC electrode is able to detect 10 µM dopamine and has improved sensitivity compared to platinum. Compared to carbon fiber electrodes, the DLC electrode is more stable because the background current is much lower.

Mesh-based method for measuring intracranial volume in patients with craniosynostosis.

PURPOSE: Craniosynostosis may lead to reduced intracranial volume (ICV) and disturb normal brain growth and development. Thus, ICV is an important parameter with respect to the surgical outcome. Current methods for ICV determination from computed tomography (CT) images have drawbacks. The aim of this study was to investigate the performance of the novel mesh-based method (MBM) for ICV determination with craniosynostosis patients. METHODS: Twenty-two patients operated on for scaphocephaly were included in this study. ICVs from preoperative, one-week postoperative, and one-year postoperative CT images were measured with MBM. The level of agreement with the manual segmentation method (MSM) was determined for the measurements of preoperative and one-year postoperative datasets. Repeatability was determined with re-measurements of six datasets. Measurement time was recorded for MBM. RESULTS: Mean [Formula: see text] preoperative ICV values were 895.0 [Formula: see text] 153.1 [Formula: see text] and 896.4 [Formula: see text] 147.2 [Formula: see text] as measured with MBM and MSM, respectively. Corresponding one-year postoperative values were 1,238.3 [Formula: see text] 118.7 [Formula: see text] and 1,250.1 [Formula: see text] 117.5 [Formula: see text]. The MBM allowed ICV determination from one-week postoperative datasets. Measurement time with MBM was 4 CONCLUSIONS: MBM is an efficient method for determining the ICV of craniosynostosis patients, allowing the measurement of skulls with bony defects. The repeatability and short measurement time of MBM are attributable to the user interference and assessment of the measurement process.