SOI-MEMS Technology Research Articles

Single mask and low voltage electrothermal micromotor

This paper introduces a single-mask-and-low-voltage electrothermal micromotor driven by four symmetrical V-shaped actuators and ratchet mechanism. The 2.5 mm-diameter micromotor has been fabricated successfully by using silicon on insulator (SOI) wafers and SOI-MEMS technology. The play of micromotor is tested under microscope and indicated that it operates quite smoothly. The actual rotation speeds (rpm) of the micromotor are examined with the driving frequencies range from 1 Hz to 15 Hz at a driving voltage of 12.5 V and compared with the calculation. Experimental results show that the theoretical and measured angular speeds are quite close while the applied frequencies are lower or equal to 10 Hz.

Characterization of Residual Stress in SOI Wafers by Using MEMS Cantilever Beams.

Silicon-on-insulator (SOI) wafers are crucial raw materials in the manufacturing process of microelectromechanical systems (MEMS). Residual stresses generated inside the wafers during the fabrication process can seriously affect the performance, reliability, and yield of MEMS devices. In this paper, a low-cost method based on mechanical modeling is proposed to characterize the residual stresses in SOI wafers in order to calculate the residual stress values based on the deformation of the beams. Based on this method, the residual strain of the MEMS beam, and thus the residual stress in the SOI wafer, were experimentally determined. The results were also compared with the residual stress results calculated from the deflection of the rotating beam to demonstrate the validity of the results obtained by this method. This method provides valuable theoretical reference and data support for the design and optimization of devices based on SOI-MEMS technology. It provides a lower-cost solution for the residual stress measurement technique, making it available for a wide range of applications.

A Sensitivity Tunable Accelerometer Based on Series-Parallel Electromechanically Coupled Resonators Using Mode Localization

This paper reports a novel mode-localized resonant accelerometer, which can keep high sensitivity even over a wide range. To improve the adjustability of sensitivity, a new four degree of freedom (4-DoF) series-parallel resonator array is proposed. Three sensing resonators are mechanically coupled together in series by folding beams and the fourth sensitivity-tuning resonator is electrically coupled in parallel with the sensing system. When the stiffness perturbation caused by acceleration occurs, a change of modal amplitude ratio due to the mode localization phenomenon can be detected. By tuning the voltage on the sensitivity-tuning resonator, the sensitivity of the accelerometer can be altered to keep the amplitude ratio within a reasonable range. The theoretical model of the accelerometer is established and analyzed by numerical method. To confirm the feasibility of the design, a device fabricated by SOI-MEMS technology is tested under open-loop circuit. The measured amplitude ratio sensitivity varies from 1.14/g to 23.37/g with the change of the tuning voltage, and the sensitivity adjustment range reaches 2050%. [2019-0199]

Development of new electrostatic micro cam system driven by elastic wings

In this paper, we improve and develop a micro cam system, in which reciprocating linear movement of two electrostatic linear comb-drive actuators (ELCA) is transformed into the unilateral rotation of a cam rim through six elastic wings of motion-transmission mechanisms. The system was fabricated by using SOI-MEMS technology and only one photo mask. Our experimental results show that the new micro cam system runs stably while the driving frequency ranging from 1 to 30 Hz with the driving voltage Vpp = 100 V. In addition, the average angular velocities of the cam rim matched with the theoretical results better than the velocities measured in the previous micro cam system.

A micro transmission system based on SOI-MEMS technology: improvement and characteristics

In this paper, we have improved and developed a micro transmission system (MTS) with combination of the comb-drive actuators, the ratchet mechanism and elastic structures like beams, springs, etc. The MTS has been fabricated by a SOI-MEMS technology using single photo mask. The system is equipped with two parallel ratchet-actuators on both sides, and can stably drive a four-spring micro container with different velocities in proportion to the driving frequencies up to 40 Hz. Our experiments showed that the MTS not only works stably with one container, but also it can drive smoothly four containers at the same time with the applied voltage of 110 V. The results confirmed a higher stability and better loading capacity of the improved system.

An Electromagnetic Vibrating Ring Gyroscope Using SOI-MEMS Technology

This paper presents the design, fabrication and tests of an electro-magnetic vibrating ring gyroscope based on a control system and SOI-MEMS technology. The control system, including variable gain control (VGC), drive-frequency control and regulation module, is designed to improve mode matching. In device fabrication, and buffered hydrofluoric acid (BHF) solution is used to remove the buried oxide layer and release the suspended spring. Meanwhile, a compensate disk and negative photo resist (AZ303) coated on the backside of the wafer are employed to weaken the Lag and Footing effects during through-wafer etching process. The design of the gyroscope is optimized by FEA simulation and the fabricated devices show a rather good performance.

Fabrication of a Pendulous Resonant Micro-Machined Biosensor for Direct Liquid Detection

This paper presents a pendulous resonant MEMS biosensor for liquid detection based on SOI-MEMS technology. The biosensor consists of two electromagnetically driven and sensed resonant paddles working in the torsional mode. The differential output consisted by the two paddles provides the sensor reading. 1um thick SiNx is deposited on the electrodes by plasma enhanced chemical vapor deposition (PECVD), making the biosensor capable of working in liquid directly. In device fabrication, SOI-MEMS fabrication processes were utilized, where a new modified buffered hydrofluoric acid (BHF) solution was used to remove the buried oxide layer and release the paddles. High-current drive circuit and energy compensation circuit are designed to improve the Q-factor of the paddle in liquid. Experimental experiments show that the biosensor can distinguish the density of some liquid effectively．

Differentially piezoresistive transduction of high-Q encapsulated SOI-MEMS resonators with sub-100 nm gaps.

A differentially piezoresistive (piezo-R) readout proposed for single-crystal-silicon (SCS) microelectromechanical systems (MEMS) resonators is implemented in a foundrybased resonator platform, demonstrating effective feedthrough cancellation using just simple piezoresistors from the resonator supports while maximizing their capacitively transduced driving areas. The SCS resonators are fabricated by a CMOS foundry using an SOI-MEMS technology together with a polysilicon refill process. A high electromechanical coupling coefficient is attained by the use of 50-nm transducer gap spacing. Moreover, a vacuum package of the fabricated resonators is carried out through wafer-level bonding process. In this work, the corner supporting beams of the resonator serve not only mechanical supports but also piezoresistors for detecting the motional signal, hence substantially simplifying the overall resonator design to realize the piezo-R sensing. In addition, the fabricated resonators are capable of either capacitive sensing or piezo-R detection under the same capacitive drive. To mitigate feedthrough signals from parasitics, a differential measurement configuration of the piezo-R transduction is implemented in this work, featuring more than 30-dB improvement on the feedthrough level as compared with the single-ended piezo-R counterpart and purely capacitive sensing readout. Furthermore, the high-Q design of the mechanical supports is also investigated, offering Q more than 10 000 with efficient piezo-R transduction for MEMS resonators.

Design and performance of a high loading electrostatic micro linear motor

This paper reports design and performance of a new micro linear motor (MLM) driven by electrostatic comb-drive actuators based on SOI-MEMS technology. In this motor, a shuttle with six wings on the each side is moved by the electrostatic comb-drive actuators through ratchet teeth in the direction perpendicular to the movement direction of the ratchet racks. The MLM was fabricated from SOI (silicon on insulator) wafer by using only one photo mask. The bidirectional movement of the shuttle has been tested with AC driving voltage of Vpp = 100 V and driving frequency ranged from 1 to 10 Hz. In our experiments, the displacement of the shuttle after each step is approximately 10 µm and the obtained travel equals 500 µm. Through measurement of the deflection of a test beam, the load capacity is estimated as 352.97 µN. This MLM has dimensions of 5 × 5 mm2 and can be applied in a micro assembling system to lift/drop micro samples or in micro transportation systems, etc.

A SOI-MEMS Based Resonant Barometric Pressure Sensor with Differential Output

This paper presents a laterally driven resonant barometric pressure sensor fabricated using SOI-MEMS technology. In this device, pressure under measurement causes a deflection of a pressure-sensitive silicon square diaphragm, which is further translated to stress build up in H style doubly-clamped micro beams, leading to resonant frequency shift. In device fabrication, SOI-MEMS fabrication processes were utilized, where a new modified buffered hydrofluoric acid (BHF) solution was used to remove the buried oxide layer and release the suspended resonant beams. Experimental results recorded a device resolution of 10Pa, a nonlinearity of 0.04% and a temperature coefficient of-0.04% F.S/°C in the range of-40°C to 30°C. The long-term stability error of the proposed device was quantified as 0.05% F.S over the past 3 months.

Micro cam system driven by electrostatic comb-drive actuators based on SOI-MEMS technology

This paper reports a design and fabrication process of a micro cam system (MCS) with a flat-faced translating follower. The cam rim with cover diameter of 2.4 mm is driven by four electrostatic comb-drive actuators (ECA). Reciprocating motion of the ECAs is converted to unidirectional rotating movement of the outer cam rim through ratchet and anti-reverse mechanisms. The MCS was fabricated by using SOI (silicon on insulator) wafer with 30 μm thick device layer, and only one mask. Driven by periodic voltage with different frequencies, the performance of the MCS was successfully tested. In our experiment, when the system was run by the minimal driving voltage of 80 V, the obtained stroke of the follower was 160 μm. In addition, the system can run smoothly while applying the force of 31.3 μN on the follower. The MCS can be applied in micro valve structures, in micro assembling systems, etc.

Design of an SOI-MEMS high resolution capacitive type single axis accelerometer

In recent years, high resolution micro accelerometers are increasingly finding various applications in different segments of life. The current work deals with the design of a high resolution single axis accelerometer based on SOI-MEMS technology. Accordingly two different approaches for designing comb type, capacitive, SOI-MEMS accelerometer is presented. Initially a system level approach using a simulation platform from SABER is carried out to obtain the basic design. Later, a device level design is carried out by building three dimensional (3D) geometric models using finite element (FE) simulations through CoventorWare software. Different design parameters like mechanical and electrical sensitivity, capacitance values, resonant frequency, etc. are obtained in either of the cases and compared. The design is optimized based on the overall sensitivity and the system noise level both electrical and mechanical, respectively. The complete design is worked out in accordance with the silicon on insulator based multiuser MEMS fabrication processes (MUMPs) technology from MEMSCAP foundry.

A Study on Electrostatic Tuning of Resonant Frequency for SOI-MEMS Resonators

Electrostatic tuning characteristics of the electrostatic resonators fabricated using SOI-MEMS technology with various configurations and voltage bias conditions were systematically studied using the FEM simulator. The basic structures of the resonators consist of a 1mm×1mm proof mass and four 200μm-long, 3μm-wide beams, whose thicknesses are 10μm, resulting in the resonant frequencies of the fundamental resonant mode without applied voltages which were about 5kHz. The resonant frequencies of the resonators with parallel-plate electrodes decreased quadratically with the applied voltage, while those of the resonators with comb electrodes gave no significant change. When the influence of the substrate was taken into consideration, the resonant frequency change by the applied voltage was reduced by several percents.

A resonant accelerometer with two-stage microleverage mechanisms fabricated by SOI-MEMS technology

We present the design, fabrication, and testing of a push-pull differential resonant accelerometer with double-ended-tuning-fork (DETF) as the inertial force sensor. The accelerometer is fabricated with the silicon-on-insulator microelectromechanical systems (MEMS) technology that bridges surface micromachining and bulk micromachining by integrating the 50-/spl mu/m-thick high-aspect ratio MEMS structure with the standard circuit foundry process. Two DETF resonators serve as the force sensor measuring the acceleration through a frequency shift caused by the inertial force acting as axial loading. Two-stage microleverage mechanisms with an amplification factor of 80 are designed for force amplification to increase the overall sensitivity to 160 Hz/g, which is confirmed by the experimental value of 158 Hz/g. Trans-resistance amplifiers are designed and integrated on the same chip for output signal amplification and processing. The 50-/spl mu/m thickness of the high-aspect ratio MEMS structure has no effect on the amplification factor of the mechanism but contributes to a greater capacitance force; therefore, the resonator can be actuated by a much lower ac voltage comparing to the 2-/spl mu/m-thick DETF resonators. The testing results agree with the designed sensitivity for static acceleration.