Flexible electronics attached to skin for healthcare, such as epidermal electronics, has to struggle with biocompatibility and adapt to specified environment of skin with respect to breath and perspiration. Here, we report a strategy for biocompatible flexible temperature sensors, inspired by skin, possessing the excellent permeability of air and high quality of water-proof by using semipermeable film with porous structures as substrate. We attach such temperature sensors to underarm and forearm to measure the axillary temperature and body surface temperature respectively. The volunteer wears such sensors for 24 hours with two times of shower and the in vitro test shows no sign of maceration or stimulation to the skin. Especially, precise temperature changes on skin surface caused by flowing air and water dropping are also measured to validate the accuracy and dynamical response. The results show that the biocompatible temperature sensor is soft and breathable on the human skin and has the excellent accuracy compared to mercury thermometer. This demonstrates the possibility and feasibility of fully using the sensors in long term body temperature sensing for medical use as well as sensing function of artificial skin for robots or prosthesis.

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Breathable and Stretchable Temperature Sensors Inspired by Skin

We have presented an RF MEMS tuneable lowpass filter. Both distributed transmission lines and RF MEMS capacitances were used to replace the lumped elements. The use of RF MEMS capacitances gives the flexibility of tuning the cutoff frequency of the lowpass filter. We have designed a low-pass filter at 9–12 GHz cutoff frequency using the theory of stepped impedance transmission lines. A prototype of the filter has been fabricated using parallel plate capacitances. The variable shunt capacitances are formed by a combination of a number of parallel plate RF MEMS capacitances. The cutoff frequency is tuned from C to X band by actuating different combinations of parallel capacitive bridges. The measurement results agree well with the simulation result.

/pdf/tunable-lowpass-filter-with-rf-mems-capacitance-and-2j93v7fbfm.pdf

Tunable lowpass filter with RF MEMS capacitance and transmission line

We present an all-aluminum MEMS process (Al-MEMS) for the fabrication of large-gap electrostatic actuators with process steps that are compatible with the future use of underlying, pre-fabricated CMOS control circuitry. The process is purely additive above the substrate as opposed to processes that depend on etching pits into the silicon, and thereby permits a high degree of design freedom. Multilayer aluminum metallization is used with organic sacrificial layers to build up the actuator structures. Oxygen-based dry etching is used to remove the sacrificial layers. While this approach has been previously used by other investigators to fabricate optical modulators and displays, the specific process presented herein has been optimized for driving mechanical actuators with relatively large travels. The process is also intended to provide flexibility for design and future enhancements. For example, the gap height between the actuator and the underlying electrode(s) can be set using an adjustable polyimide sacrificial layer and aluminum \"post\" deposition step. Several Al-MEMS electrostatic structures designed for use as mechanical actuators are presented as well as some measured actuation characteristics. >

Flexible, dry-released process for aluminum electrostatic actuators

Polyimide has become a main material for sacrificial layer in MEMS switch. Before spinning, poly-imide needs to undergo low- and high-temperature thermal treatment, so as to meet the requirement of lithography. The cure process after developing and etching makes polyimide flat and etch-proof. Different cure temperature and time affects the behavior of polyimide. After air-bridge is made, polyimide must be removed by etching. The experiment shows that when cure temperature is lower than 170℃, polyimide can be eliminated by alkaline solution; but when cure temperature is higher than 200 ℃, plasma etching with oxygen is required to remove polyimide.

An Investigation into Polyimide Sacrificial Layer for RF/MW MEMS Switch

Miniaturization techniques for antenna designs based on fractal geometries are of growing interest in wireless communications. This letter demonstrates miniature fractal antenna designed and fabricated on the high-resistivity Si substrate. This antenna is used for SoC (system on the chip). The proposed concept also can be extended to linear antenna arrays or to more complex antenna structures with large improvements in antenna performance. To this end, the effectiveness of the approach is confirmed by simulated and experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 363–365, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23079

Design and fabrication of miniaturized loop dual‐band fractal antenna based on the silicon substrate

Due to the trade secrets and intellectual property, there are still many aspects of MEMS switches which are not understand well and are currently under investigation. In this paper, our report shows that MEMS can be released using O2 and a little carbon powder at the same time. The relationship between the removing polyimide time and the cure temperature is presented using carbon powder in the quartz vacuum cavity when etching polyimide sacrificial layer. It greatly reduces removing polyimide sacrificial layer time. It is highly important for MEMS fabrication process technology. The process is capable of various applications in surface micromachining process, and can be applied in fabricating RF MEMS switches, tunable capacitors, high-Q suspended inductors and suspended-gate MOSFETs.

A Novel Method of Removing Polyimide Sacrificial Layer

Reconfigurability in an antenna system is a desired characteristic that has been the focus of much research in recent years. The paper demonstrates miniature re-configurable antenna designed and fabricated on the high resistivity Si substrate. This antenna can integrate with a novel microelectromechanical systems actuator for reconfiguring the operating frequency and is used for SoC (System on the chip). The switching between the two different frequency bands is achieved through the use of RF-MEMS switches. According to the open/closed experiment results, when switch is on and off, the antenna operating frequency is 12.3 GHz and 13.1 GHz with low return loss, respectively. The final model radiates at two widely separated frequencies with very similar radiation patterns. The proposed concept can be extended to reconfigurable linear antenna arrays or to more complex antenna structures with large improvements in antenna performance. It is important for the next generation wireless communications and integrated antenna system on the chip. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2413–2416, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21979

Re‐configurable Kμ dual‐bands slot antenna using mems switches

This paper presents the design and modeling of a unit cell for reconfigurable microwave microelectromechanical systems (MEMS) low pass filters (LPF), with reconfigurable inductance and capacitance. Lumped elements are introduced here to approximate the characteristics of the distributed filters, and then optimization is performed to obtain the superior characteristics as needed. LPFs with arbitrary cut-off frequency between 10GHz to 30GHz can be optimized corresponding to this model. Using this prototype, the reconfigurable LPF has a cut-off frequency switching from 7.8GHz to 15.3GHz, with ripple below 2dB and out-of-band rejection better than 40dB in both states, which demonstrates the validation of the proposed model

Design and modeling of reconfigurable MEMS low pass filter

The paper demonstrates miniature reconfigurable antenna designed and fabricated on the high resistivity Si substrate This antenna can integrate with a microelectromechanical system (MEMS) actuator for reconfiguring the operating frequency and is used for SOC (system on the chip) The switching between the two different frequency bands is achieved through the use of RF-MEMS switches According to the ideal open/closed experiment results, when switch is on and off, the antenna operating frequency is 277GHz and 395GHz with low return loss, respectively It is important for the next generation wireless communications and integrated antenna system on the chip

Miao Cai

Papers

A Novel Method of Removing Polyimide Sacrificial Layer

Re‐configurable Kμ dual‐bands slot antenna using mems switches

Design and modeling of reconfigurable MEMS low pass filter

Fitting SOC miniature MEMS reconfigurable antenna