Infrared emitter (IR) with photonic crystal structure formed by a hexagonal array of holes has been designed. The
processes for fabricating the emitter are developed basing on using silicon-on-insulator (SOI) wafer. The emission
spectrum of the IR emitter is measured with spectroradiometer. The experimental results show that the infrared emitter
exhibits a strong narrow-band emission in middle infrared range. The wavelengths of the measured emission peaks agree
well with the theoretical prediction.
A high-visibility infrared array emitter for identification and display screen has been demonstrated. The silicon-based MEMS Infrared emitter was fabricated on silicon-on-insulator (SOI) wafer. The infrared emitter cell can be operated at 1100K with a total power of 2.5W, and the modulation frequency can reach to 50Hz at 50 modulation depth. The Infrared array emitters consist of 1*2, 2*2 and 3*3 emitter cells, respectively, which can be made as an infrared indicator or display screen for object identification and information displaying with a recognition ranges determined by input power. The experiments shown that due to the problems of structure and stress, the modulation frequency and lifetime of the infrared array emitter were reduced with increasing array dimension.
In spin electronic devices, passing a spin-polarized current through the device is a better way to switch the magnetic
configuration than applying an external magnetic field with an external current line, because there are several drawbacks
associated with the use of external magnetic fields in terms of energy consumption and the risk of crosstalk. One good
method is using a current to induce domain wall motion from a constriction in a spin-valve structure, which generates
much interest in the case of spin-dependent electron transport across a nanocontact or a nanoconstriction. The samples
are fabricated on a SiO<sub>2</sub>/Si substrate using electron beam lithography and a lift-off technique. Electron beam lithography
was used to define the nanocontact structure and radio frequency magnetic sputtering with pure Ar was used to deposit
an Al<sub>50</sub>Fe<sub>50</sub> alloy layer about 30 nm thick and an Au cap-layer about 2 nm thick. Ultrasonic assisted lift-off in acetone is
used to obtain the wire and the constriction. The I-V measurement is performed at room temperature without applied
magnetic field. A sharp drop in resistance was observed in the 50-nm-wide nanocontact, which is attributed to the
removal of the domain wall from the contact by the reflection of spin polarized electron. In the low resistance state, no
domain wall is pinned at the contact, while in the high resistance state the presence of a domain wall must be responsible
for the additional resistance, which is the domain wall resistance.
An improved fabrication technique for silicon-based MEMS (MEMS: microelectromechanical systems) Infrared (IR) emitter is presented. The IR emitter was fabricated on silicon-on-insulator (SOI) wafer. The resistively heated polysilicon membrane fabricated by using deep reactive ion etching (DRIE) process on backside of SOI wafer has a low thermal mass structure, thus this IR-emitter can be modulated at high frequency. Additionally, the usage of the DRIE process instead of the wet etching process provides a more optimum design for the chip dimension. An appropriate boron (B) dope was used to realize the infrared absorption of silicon or infrared transparence of silicon for achieving self-heating or body emitting effect. By using the SOI wafer, the fabrication processes are simplified, and the production costs are decreased. The membrane temperature and emission spectrum of IR emitter were measured with thermal imaging system and spectroradiometer. The experimental results show that the IR emitter exhibits a strong emission in middle infrared range, and the modulation frequency can reach to 45Hz at 50% modulation depth. It is expected that this IR-emitter can be used in low cost sensing system.
For higher-power-handling RF MEMS switches, the design of the switch is based on fixed-fixed beam capacitive structure with electrostatic actuation. Such RF MEMS switches are perceived to be unreliable because of the stiction and screening of the beam caused by charge accumulation in the dielectric layer. The research effort for a robust RF MEMS solution has been made for more than a decade. In this paper the models for stiction and screening caused by charge accumulation have been reviewed. As the first part of this paper, the possible charging mechanisms will be described, such as, 1) the dielectric charging arises from charges distributed throughout the dielectric material, 2) the presence of charges at the dielectric interface. In order to avoid the charge accumulation, trapped charges in the dielectric layer have to quickly vanish. Relaxing mechanisms of short time must be created inside of the dielectric for quick charge recombination. The second part of this paper will report the recent effort to create relaxing mechanisms of short time by using, such as doping dielectric, nano-composite dielectrics, or multi-layer stack of dielectric. Actuation wave form dependence of the charge accumulation will be also presented.
RF MEMS capacitive switches hold great promise in commercial, aerospace, and military applications. However,
their commercialization is hindered by reliability concerns: charging effect in the dielectric layer can cause irreversible
stiction of the actuating part of the switch. Presently, a popular method to investigate the charging/discharging in the
dielectric layer is to measure an actual RF MEMS capacitive switch, which means a high experimental cost in fabricating
MEMS switch devices.
In this paper, a Metal-Insulator-Semiconductor (MIS) capacitor is used to investigate the charge accumulation in
the dielectric layer of RF MEMS switches. By measuring the capacitance versus voltage (C-V) curves of MIS capacitor
after voltage stressing, the dielectric charging/discharging characteristics are obtained. The experiment results indicate
that the injected charges from the metal bridge in RF MEMS switches are responsible for stiction phenomena. In SiNx
dielectric, the hole capture is more favored over electron capture, and the trapped charges tend to inhibit the charges
further injecting. The effects of the actuation voltage waveform on the charge accumulation in the dielectric layer were
investigated. It is verified that the tailored actuation voltage waveforms can be used to improve the reliability of RF
MEMS capacitive switches.
In this paper, our work is focusing on investigating the mechanisms of the charge accumulation in dielectric layer of RF
MEMS capacitive switches. In our experiments, silicon-nitride and silicon-oxide composite films, e.g., SiO<sub>2</sub>+Si<sub>3</sub>N<sub>4</sub> and
SiO<sub>2</sub>+Si<sub>3</sub>N<sub>4</sub>+SiO<sub>2</sub> films are chosen as the dielectric layers for study. The composite films were prepared by thermal
oxidation and PECVD process. The Metal-Insulator-Semiconductor (MIS) structure was produced by using the
composite films as the dielectric layer. The capacitance versus voltage (C-V) measurement is employed to study the
space charge injection and relaxation process in the composite films. The results show that the charge accumulation can
be reduced by using the composite films structure.
In this paper, a capacitive vibration-to-electrical energy harvester was designed. An integrated process flow for
fabricating the designed capacitive harvester is presented. For overcoming the disadvantage of depending on external
power source in capacitive energy harvester, two parallel electrodes with different work functions are used as the two
electrodes of the capacitor to generate a build-in voltage for initially charging the capacitor. The device is a sandwich
structure of silicon layer in two glass layers with area of about 1 cm<sup>2</sup>. The silicon structure is fabricated by using
silicon-on-insulator (SOI) wafer. The glass wafers are anodic bonded on to both sides of the SOI wafer to create a
vacuum sealed package.
Dielectric charging is one of the main problems leading to failure of capacitive RF MEMS switches. In this work
phosphorus or boron ions were implanted into dielectric layer by ion implantation. After dielectric layer modification by
ion implantation, we focus on investigation of the mechanisms of the charge accumulation and recombination after the
sample electrically stressed with 80 V for 30 seconds. A
Metal-Insulator-Semiconductor (MIS) capacitor structure is
used for such an investigation. Silicon nitride films as the insulator in MIS structure were deposited by LPCVD process.
The space charge accumulation in the silicon nitride film can be characterized by Capacitance-Voltage (C-V)
measurement. Because of the ionization of the gas in the operating environment of the switch, ion injection by actuation
voltage during the operation of the RF MEMS switch will play the role to enhance the charge accumulation in the
dielectric layer. Our work offers a principle to understand the effect of the operating environment to the lifetime and
reliability of the RF capacitive MEMS switches.
A vibration-powered micro-power-generator has been presented in this paper, which has integrated two different energy
harvesting mechanisms, e.g., Capacitive and Piezoelectric Mechanisms. The periodic vibration of the mass on movable
electrode causes the variation of the capacitance, and the strain in the piezoelectric film. These two mechanisms can
harvest the vibration energy and generate current in the output circuit. By using two different metals with large difference
in working function as the two electrodes of the capacitor, our design, the combination of these two different scavenge
mechanisms, can overcome the dependence of the traditional capacitive converter on the separate voltage source and
improve the efficiency of power conversion. The volume of the designed device is less than 0.8 cm<sup>3</sup>. The simulated
results reveal that this energy converter can provide an average output power of 82.21μW at an external vibration with a
frequency of 111.4 Hz and amplitude of 0.2g.
An ultra-wide-band frequency response measurement system for optoelectronic devices has been established using the optical heterodyne method utilizing a tunable laser and a wavelength-fixed distributed feedback laser. By controlling the laser diode cavity length, the beat frequency is swept from DC to hundreds GHz. An outstanding advantage is that this measurement system does not need any high-speed light modulation source and additional calibration. In this measurement, two types of different O/E receivers have been tested, and 3 dB bandwidths measured by this system were 14.4GHz and 40GHz, respectively. The comparisons between experimental data and that from manufacturer show that this method is accurate and easy to carry out.