https://www.tandfonline.com/doi/pdf/10.1080/14686996.2018.1530938

Thermoelectric materials and applications for energy harvesting power generation

The photoluminescence signals of a graphene/MoS2 heterostructural stacking film are sensitive to environmental charges, which allows the single-base sequence-selective detection of DNA hybridization with sensitivity to the level of aM.

https://ir.nctu.edu.tw:443/bitstream/11536/24868/1/000339661600011.pdf

Graphene/MoS2 Heterostructures for Ultrasensitive Detection of DNA Hybridisation

The wave nature of electrons in low-dimensional structures manifests itself in conventional electrical measurements as a quantum correction to the classical conductance. This correction comes from the interference of scattered electrons which results in electron localisation and therefore a decrease of the conductance. In graphene, where the charge carriers are chiral and have an additional (Berry) phase of \pi, the quantum interference is expected to lead to anti-localisation: an increase of the conductance accompanied by negative magnetoconductance (a decrease of conductance in magnetic field). Here we observe such negative magnetoconductance which is a direct consequence of the chirality of electrons in graphene. We show that graphene is a unique two-dimensional material in that, depending on experimental conditions, it can demonstrate both localisation and anti-localisation effects. We also show that quantum interference in graphene can survive at unusually high temperatures, up to T~200 K.

Transition between electron localisation and antilocalisation in graphene

Thermoelectricity for IoT – A review

The detection techniques used in biosensors can be broadly classified into label-based and label-free. Label-based detection relies on the specific properties of labels for detecting a particular target. In contrast, label-free detection is suitable for the target molecules that are not labeled or the screening of analytes which are not easy to tag. Also, more types of label-free biosensors have emerged with developments in biotechnology. The latest developed techniques in label-free biosensors, such as field-effect transistors-based biosensors including carbon nanotube field-effect transistor biosensors, graphene field-effect transistor biosensors and silicon nanowire field-effect transistor biosensors, magnetoelastic biosensors, optical-based biosensors, surface stress-based biosensors and other type of biosensors based on the nanotechnology are discussed. The sensing principles, configurations, sensing performance, applications, advantages and restriction of different label-free based biosensor...

Progress of new label-free techniques for biosensors: a review.

Silicon nanowire (SiNW) field effect transistors (FETs) have emerged as powerful sensors for ultrasensitive, direct electrical readout, and label-free biological/chemical detection. The sensing mechanism of SiNW-FET can be understood in terms of the change in charge density at the SiNW surface after hybridization. So far, there have been limited systematic studies on fundamental factors related to device sensitivity to further make clear the overall effect on sensing sensitivity. Here, we present an analytical result for our triangle cross-section wire for predicting the sensitivity of nanowire surface-charge sensors. It was confirmed through sensing experiments that the back-gated SiNW-FET sensor had the highest percentage current response in the subthreshold regime and the sensor performance could be optimized in low buffer ionic strength and at moderate probe concentration. The optimized SiNW-FET nanosensor revealed ultrahigh sensitivity for rapid and reliable detection of target DNA with a detection limit of 0.1 fM and high specificity for single-nucleotide polymorphism discrimination. In our work, enhanced sensing of biological species by optimization of operating parameters and fundamental understanding for SiNW FET detection limit was obtained.

Enhanced sensing of nucleic acids with silicon nanowire field effect transistor biosensors.

This paper presents a CMOS MEMS-based thermoelectric energy generator (TEG) device with an efficient heat dissipation path. For present CMOS MEMS-based thermoelectric generator devices, the output performance is greatly limited by the high thermal-contact resistance in the system. For the device proposed in the work, the silicon substrate is etched into two comb-shaped blocks thermally isolated from each other, which form the hot and cold sides. Thin-film-based thermal legs are densely located between the two blocks along the winding split line. Low internal thermal-contact resistance is achieved with the symmetrical thermal structure. When the TEG device is embedded between the heat source and heat sink, the heat loss can be well controlled with flat thermal-contact pads of the device. For a full device with 900 n/p-polysilicon thermocouples, the measured open-circuit voltage reaches as high as 146 mV K−1, and the power factor reaches almost five times higher value compared to the previously reported results. A test system integrated with a single device presents an open-circuit voltage of 110 mV K−1 when forcibly cooled by a Peltier cooler, or 26 mV K−1 when cooled by ambient air.

https://iopscience.iop.org/article/10.1088/0960-1317/22/10/105011/pdf

CMOS MEMS-based thermoelectric generator with an efficient heat dissipation path

A wafer-level vacuum package with silicon bumps and electrical feedthroughs on the cap wafer is developed for a microelectromechanical systems (MEMS) resonator device. A MEMS resonator wafer and a cap wafer are bonded together in a vacuum chamber using glass frit bonding. The cap wafer not only provides a vacuum chamber to protect the movable resonator structure and improve the resonant performance but also realizes the redistribution of the electrical feedthroughs by using the silicon bumps. The silicon bumps provide vertical interconnections between the cap wafer and the resonator wafer, which realizes the bonding pads “transferring” from the resonator wafer to the cap wafer. A gold-aluminum eutectic is used to ensure electrical contacts between the cap wafer and the device wafer. The device fabrication and glass frit hermetic bonding process as well as the packaged MEMS resonator characterization are presented in this paper. Experimental results show that the wafer-level vacuum-packaged MEMS resonator results in over 100× higher quality factor (Q) than the resonator vibrating in atmosphere pressure, which confirms the transmission performance improvement due to vacuum packaging. Vacuum inside the package is measured indirectly by measuring the Q of the MEMS resonator inside the package. The experimental results indicate that vacuum about 1 mbar can be sealed in this approach.

Wafer-Level Vacuum Packaging for MEMS Resonators Using Glass Frit Bonding

The unique anisotropic wet-etching mechanism of a (111) silicon wafer facilitates the highly controllable top-down fabrication of silicon nanowires (SiNWs) with conventional microfabrication technology. The fabrication process is compatible with the surface manufacturing technique, which is employed to build a nanowire-based field-effect transistor structure on the fabricated SiNW.

Top-down fabricated silicon-nanowire-based field-effect transistor device on a (111) silicon wafer.

Wafer-level isotropic etching of silicon with XeF2 gas has been investigated for microelectromechanical-system (MEMS) fabrication. Because of the large exposed silicon area in the wafer-level process, XeF2 gas diffusion in the wafer-level process is different from the chip-level process. The silicon etch rate for the wafer-level XeF2 process is much smaller than chip-level XeF2 etching. Additionally, the silicon etch rate drops off as the etching time increased. The aperture size effect is apparent in the wafer-level XeF2 processing. However, for etching windows with a large size, the aperture size effect will be minimized. Both vertical and lateral aperture size effects depend on the number of etch cycle. Although slight anisotropy is also observed, wafer-level XeF2 etching shows a better isotropy than the chip-level process. Compared with the chip-level process, wafer-level XeF2 etching shows a large etch rate for SiO2. The etch selectivity between silicon and SiO2 is lower than 1000:1. Based on the characteristics of XeF2 etching, the layout design rule for the MEMS device with XeF2 releasing is developed and demonstrated.

Yuchen Wang

Papers

Enhanced sensing of nucleic acids with silicon nanowire field effect transistor biosensors.

CMOS MEMS-based thermoelectric generator with an efficient heat dissipation path

Wafer-Level Vacuum Packaging for MEMS Resonators Using Glass Frit Bonding

Top-down fabricated silicon-nanowire-based field-effect transistor device on a (111) silicon wafer.

Isotropic Silicon Etching With $\hbox{XeF}_{2}$ Gas for Wafer-Level Micromachining Applications