CMOS-MEMS Process Research Articles

Diode-Like Field Emission Devices Fabricated by Standard 0.35-μm CMOS MEMS Process

Diode-Like Field Emission Devices Fabricated by Standard 0.35-μm CMOS MEMS Process

Investigation of Laser Ablation Quality Based on Data Science and Machine Learning XGBoost Classifier

This work proposes a matching data science approach for the laser ablation quality, reb, the study of Si3N4 film based on supervised machine learning classifiers in the CMOS-MEMS process. The study demonstrates that there exists an energy threshold, Eth, for laser ablation. If the laser energy surpasses this threshold, increasing the interval time will not contribute significantly to the recovery of pulse laser energy. Thus, reb enhancement is limited. When the energy is greater than 0.258 mJ, there exists a critical value of interval time at which the reb value is relatively low for each energy level, respectively. In addition, the variation of reb, Δreb, is independent of the interval time at the invariant point of energy between 0.32 mJ and 0.36 mJ. Energy and interval time exhibit a Pearson correlation of 0.82 and 0.53 with reb, respectively. To maintain Δreb below 0.15, green laser ablation of Si3N4 at operating energies of 0.258–0.378 mJ can adopt a baseline interval time of the initial baseline multiplied by 1/∜2. Additionally, for operating energies of 0.288–0.378 mJ during Si3N4 laser ablation, Δreb can be kept below 0.1. With the forced partition methods, namely, the k-means method and percentile method, the XGBoost (v 2.0.3) classifier maintains a competitive accuracy across test sizes of 0.20–0.40, outperforming the machine learning algorithms Random Forest and Logistic Regression, with the highest accuracy of 0.78 at a test size of 0.20.

Design and characterization of an accelerometer with low cross axis sensitivity

An out-of-plane capacitive accelerometer with low cross axis sensitivity at high accelerations based on a CMOS MEMS process is developed. A truss frame with a high ratio of in-plane stiffness to out-of-plane stiffness is designed to suspend the proof mass of the accelerometer. The configuration of the proof mass with four auxiliary masses surrounding a main mass boosts the sensitivity of the accelerometer in the out-of-plane direction. A sensing circuit with period modulated output signals is realized by applying a relaxation oscillator to the sensing capacitors. The relaxation oscillator converts the capacitance changes to frequency variations. Analytical models are developed to assist the design of the accelerometer. The nonlinearity and sensitivity of the accelerometer are 1.1% and 754 Hz/g, respectively, for the acceleration ranging from 0 to 9 g. Measured cross-axis sensitivity is 4% at an acceleration of 9 g. The power consumption is 1.7 mW under a 1.8 V supply.

CMOS MEMS Design and Fabrication Platform

This article mainly describes the technology related to the CMOS MEMS process platform provided by the Taiwan Semiconductor Research Institute (TSRI), including the process flow, design verification, back-end dicing, and packaging of the CMOS MEMS integrated sensing single chip. The front-end CMOS processes can be a standard 0.35 or 0.18 µm CMOS process, or even a BCD high-voltage process. Some academic designs also utilize this platform for in-house post-CMOS process. Finally, the article also explains in detail the CMOS MEMS design flowchart and implementation method provided by TSRI.

A Test IC for Wafer-Level Characterization of an IntraCMOS-MEMS Fabrication Process

Monitoring of fabrication processes and the measurement of the electrical and mechanical properties of materials and devices at the silicon-wafer level are of vital importance on integrated system technologies. In this work, a test integrated circuit (IC) for the development of an IntraCMOS-MEMS fabrication process is presented. The test devices contained in the test IC are designed in such a way that 1) they can be used in CMOS-MEMS fabrication technologies using different materials, 2) take into account the capabilities of the manufacturing infrastructure, and 3) consider the selected integrated fabrication scheme; thus, any monolithic CMOS-MEMS process can be evaluated before, during and after the fabrication. The acquired data from the test devices will be useful to identify possible electrical and/or mechanical variations, in the properties of the materials used and in the performance characteristics of the devices, due to the fabrication process. The information acquired will help to adjust the simulation routines and the analytical modeling expressions. Finally, using the infrastructure of the MEMS Innovation Laboratory (LIMEMS-INAOE Mexico) preliminary experimental results are presented.

Vibration Mode Suppression in Micromechanical Resonators Using Embedded Anti- Resonating Structures

This paper presents a technique for suppressing specific resonance modes of micromechanical resonators by mechanical means. In particular, attaching multiple miniaturized beam structures with properly designed dimensions acting as anti-resonating tuned mass dampers (TMD's) to a micromechanical clamped-clamped beam (CC-beam) resonator based on a CMOS-MEMS process platform successfully attenuate the dynamic frequency response of the fundamental mode while retaining the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> harmonic mode of the CC-beam. The measured results show that the frequency transmission response of the TMD-embedded CC beam drops as much as ~12 dB compared to that of a reference resonator. An analytical model is used to study the effects of the parameter variations of the TMD structures. This technique provides an alternative approach to mechanically suppressing vibration modes for the micromechanical resonators that cannot employ the conventional quarter-wavelength support technique.

A Low-Power Low-Noise Monolithic Accelerometer with Automatic Sensor Offset Calibration

This work presents a monolithically integrated CMOS-MEMS capacitive accelerometer that uses background self-calibration in analog mode to compensate for sensor offset. Background analog calibration maintains sensor accuracy at all times, thus improving upon traditional digital calibration methods. When powered on, the calibration process automatically initiates without the need for an external controller like a microcontroller. The design requires no physical trimming techniques on the MEMS structure, and the worst zero-gram offset can be reduced to ±50 ​mg. The single-axis accelerometer was fabricated by the UMC 0.18 ​μm CMOS-MEMS process. The chip area containing the sensors and the integrated circuit is 1.94 ​mm ​× ​1.23 ​mm. Within the sensing range of ±8 ​g, the measured output noise density is around 100 μg/rtHz. This total power consumption from the 1.8 ​V supply voltage is 45 ​μW.

A Thermopile Device with Subwavelength Structure by CMOS-MEMS Technology

Besides the application of the photonic crystal for the photodetector in the visible range, the infrared devices proposed with subwavelength structure are numerically and experimentally investigated thoroughly for infrared radiation sensing in this research. Several complementary metal oxide semiconductor (CMOS) compatible thermopiles with subwavelength structure (SWS) are proposed and simulated by the FDTD method. The proposed thermopiles are fabricated by the 0.35 μm 2P4M CMOS-MEMS process in TSMC (Taiwan Semiconductor Manufacturing Company). The measurement and simulation results show that the response of these devices with SWS is higher than for those without SWS. The trend of the measurement results is consistent with that of the simulation results. Obviously, the absorption efficiency of the CMOS compatible thermopile can be enhanced when the subwavelength structure exists.

Investigation on an Active Thermoelectric Vacuum Sensor with Low Frequency Modulation

In this research, we propose and investigate a thermoelectric-type vacuum sensor with an active heater in the center of sensor under low frequency modulation. Thermal type sensor for vacuum measurement with active-heating is proposed for the suspended thermoelectric element to reach a better performance. Using the TSMC 0.35 μm CMOS-MEMS process, the proposed thermoelectric sensor with active heater is designed and fabricated with central-symmetrical thermocouples positioned. There are 64 pairs of thermocouples placed around the center of membrane and each thermocouple is designed with two kinds of material, n+ Poly and metal. The material of Metal 1 ∼ Metal 4 layers is aluminum, and titanium is used as contact layers to connect these metal layers. The total resistance of the structure with four units is measured to be about 14.8 kΩ and the resistance of each unit is about 3.7 kΩ. Four quarters of sensing units of thermopile were connected and the sensing area at the center will give a temperature difference. According to the Seebeck effect, serial connected thermocouples will produce a weak voltage difference between the hot and cold junctions after heat exchange under air convection related to vacuum pressure. The heating of thermopile by active heater is proceeded under different frequencies and the output signal is acquired with a Phase-Lock-Loop (PLL) amplifier. When the periodic heat exchange will take away the heat to cause a temperature drop of sensing area gives a corresponding periodic weak voltage between the cold and hot end of the thermocouples. According to a careful investigation of the PLL measurement with a wide range of 10 m∼100 Torr, our proposed sensing scheme based on a thermoelectric type sensor is proved for practical vacuum detection. Most of all it is proved as a new approach to use a commercial thermopile with heater, which is easier to include than a special custom design.

A low-power monolithic three-axis accelerometer with automatically sensor offset compensated and interface circuit

This work presents a monolithically integrated CMOS-MEMS three-axis capacitive accelerometer with an effective and practical method to compensate the sensor offset. By using correlated double sampling (CDS) and an automatic sensor offset compensated mechanism in the interface circuit, the purposes of low noise and low zero-gravity(zero-g) offset accelerometer are achieved. The zero-g offset compensated circuit calibrates the sensor offset in each axis. All of the calibrated procedure is executed automatically by a micro-control-unit (MCU). After calibration, the worst zero-g offset is reduced to ±50 mg and background calibration is no longer needed. The three-axis accelerometer was fabricated by using a 0.18-μm CMOS-MEMS process and the chip area containing the sensors and the integrated circuit is 2 × 2 mm2. It achieved a ±6 g sensing range and the noise was 350 μg/rtHz for the X- and Y-axes and Z-axes was 1.5 mg/rtHz with a total current consumption of 120 μA under 1.8 V.

Etching technique of high aspect ratio silicon trenches based on CMOS-MEMS process

Etching technique of high aspect ratio silicon trenches based on CMOS-MEMS process

Research on an ultra-low power thermoelectric-type anemometer

Beyond the conventional hot-wire sensor, a new thermoelectric sensor with ultra-low power consumption without heating is proposed. Using the TSMC 0.35 um CMOS-MEMS process, the thermoelectric sensor is fabricated with 32 pair of central-symmetrical thermocouples positioned. When the fluid passes through the thermopile, the fluid will take away the heat, so that a temperature difference is generated between the cold end and hot end of the thermocouples. The temperature sensor is calibrated and senses the drop of temperature at the center of membrane during the measurement. For different flow velocities, it is interesting to find that the drop of temperature is verified by the output voltage of sensing circuit from thermopile and the same for temperature sensor which behaves as a function of flow velocity. The new approach for the anemometer of sensing flow velocity is realized by our proposed thermopile which is proved to be a practical technique with ultra-low power consumption.

Research on a New Metal-N-Poly Thermoelectric Material Sensor for Vacuum Sensing with Self Heating

This paper proposes a new vacuum sensor with CMOS Metal-N-Poly thermoelectric materials which works for both thermoelectric sensing and resistive heating. A new method of vacuum measurement with self-heating is proposed based on the dual phases of heating and sensing for the same element which is realized with CMOS thermoelectric sensor. Using the TSMC 0.35 μm CMOS-MEMS process, the proposed thermoelectric sensor is designed and fabricated with standard CMOS materials of the 4th metal and N-polysilicon to form 64 pairs of central-symmetrical thermocouples. There is an air convection-sensing area at the center of membrane and is filled with array of micro-through-holes to enhance the effect of heat convection. When the air molecules move through the array of hole, the heat exchange will take away the heat to cause a temperature drop of sensing area which gives a weak voltage between the cold and hot end of the thermocouples. The heating of thermopile itself is designed at the first phase and sensing the output voltage at the second phase subsequently. According to a careful investigation of the measurement with a wide range of 10m~10k torr, our proposed sensing scheme based on a thermoelectric type sensor is proved for practical vacuum detection and most of all it is proved as a new approach to use a commercial thermopile without heater, which is easier to include than a special custom design.

A double-end-beam based infrared device fabricated using CMOS-MEMS process

Purpose Thermopile infrared (IR) detectors are one of the most important IR devices. Considering that the surface area of conventional four-end-beam (FEB)-based thermopile devices cannot be effectively used and the performance of this type of devices is relatively low, this paper aims to present a double-end-beam (DEB)-based thermopile device with high duty cycle and performance. The paper aims to discuss these issues. Design/methodology/approach Numerical analysis was conducted to show the advantages of the DEB-based thermopile devices. Findings Structural size of the DEB-based thermopiles may be further scaled down and maintain relatively higher responsivity and detectivity when compared with the FEB-based thermopiles. The authors characterized the thermoelectric properties of the device proposed in this paper, which achieves a responsivity of 1,151.14 V/W, a detectivity of 4.15 × 108 cm Hz1/2/W and a response time of 14.46 ms sensor based on DEB structure. Orginality/value The paper proposed a micro electro mechanical systems (MEMS) thermopile infrared sensor based on double-end-beam structure.

Modeling and validation of acoustic performances of micro-acoustic sources for hearing applications

We report on a micro-acoustic source based on industrial 0.35μm CMOS-MEMS process with only one additional post-process step. The fabrication flow completed with the characterization results of an electrostatic micro-acoustic source based on 0.35μm CMOS process with sacrificial SiO2 etch is shown here for the first time. The acoustic pressure in air in the vicinity of the resonant frequency (32kHz) at the distance of 10mm from the source was measured. The acoustic pressure of 12 mPa was obtained when the source was driven by an AC signal of 6VAC and a DC bias of 8VDC.

System-in Package of Integrated Humidity Sensor Using CMOS-MEMS Technology.

Temperature/humidity microchips with micropump were fabricated using a CMOS-MEMS process and combined with ZigBee modules to implement a sensor system in package (SIP) for a ubiquitous sensor network (USN) and/or a wireless communication system. The current of a diode temperature sensor to temperature and a normalized current of FET humidity sensor to relative humidity showed linear characteristics, respectively, and the use of the micropump has enabled a faster response. A wireless reception module using the same protocol as that in transmission systems processed the received data within 10 m and showed temperature and humidity values in the display.

Micro-acoustic Source for Hearing Applications Fabricated with 0.35 μm CMOS-MEMS Process

We report on a micro-acoustic source based on industrial 0.35μm CMOS-MEMS process with only one additional post-process step. The fabrication flow completed with the characterization results of an electrostatic micro-acoustic source based on 0.35μm CMOS process with sacrificial SiO2 etch is shown here for the first time. The acoustic pressure in air in the vicinity of the resonant frequency (32,2 kHz) at the distance of 10 mm from the source was measured. The acoustic pressure of 12 mPa was obtained when the source was driven by AC signal of 6 Vp-p and the DC bias of 8 V.

Single-Chip CMOS-MEMS Dual Mode Scanning Microwave Microscope

We present the design, fabrication and experimental validation of an integrated Scanning Microwave Microscopy (SMM)/Atomic Force Microscopy (AFM) system that does not require the use of a conventional laser-based AFM. Microfabricated SMM probes are collocated with piezoresistive strain-based sensing AFM probes in a CMOS-MEMS process, and are actuated by integrated electrothermal scanners. Integration of AFM enables dual mode imaging (topography and electrical properties) and more importantly, it enables control over tip-sample distance, which is crucial for accurate SMM imaging. This design is unique in the sense that the tip can be scanned over the sample in 3 degrees of freedom, over a 20 μm×10 μm×30 μm scan range in the x, y, and z directions respectively. We fabricate our device by using a standard foundry CMOS process followed by in-house maskless MEMS post processing to release the devices. Single-chip SMM/AFM devices with integrated 1-D and 3-D actuation are thus obtained. These devices can be used to modulate the tip-sample separation to underlying samples with a periodic signal, improving immunity to long-term system drifts. We also investigate the effect of tip-sample separation on the resolution of the instrument. To increase measurement sensitivity, a single-stub matching network has been used to match the high tip-to-sample impedance to the 50 ohm characteristic impedance of a performance network analyzer. Measurement results of the CMOS-MEMS SMM are presented to verify the proposed concept.

An optimal design of thermal-actuated and piezoresistive-sensed CMOS-MEMS resonant sensor

This paper proposes an optimal design of the thermal-actuated, piezoresistive-sensed resonator fabricated by a foundry-provided CMOS-MEMS process. The optimal design is achieved both by quantitatively comparing the mechanical properties of different composite films as well as by deriving an analytical model for determining the device dimensions. The analytical model includes a stress model of an asymmetric mechanical structure and a piezoresistivity model of the heavily doped, n-type polysilicon film. The analytical model predicts that the optimal length of the displacement sensor is 200 μm when the thermal actuator is 200 μm in length and the absorption plate is 100 μm in length. Additionally, the model predicts the resistivity of the polysilicon film of (6.8 ± 2.2) mΩ cm and the gauge factor of (6.8 ± 2.9) when the grain size is (250 ± 100) nm. Experimental results agree well with simulation results. Experimental data show that the resonant frequency of the device is 80.06 kHz and shifts to 79.8 kHz when a brick of Pt mass is deposited on the resonator. The mass of the Pt estimated from the frequency shift is 4.5419 × 10−12 kg, while estimated from the measured dimension is 4.4204 × 10−12 kg. Sensitivity of the resonant sensor is calculated to be 1.8 × 102 Hz ng−1. Experimental results further show that the polysilicon film used in the experiments has a grain size of (241 ± 105) nm, an average gauge factor of 5.56 and average resistivity of 5.5 mΩ cm.

&lt;i&gt;In Situ&lt;/i&gt; Measurement of Elastic Modulus of Individual Layers for Composite Thin Films by MEMS Test Structures

In this paper, a direct and simple method to characterize the elastic modulus of individual layers for composite films byin situmeasuring of MEMS test structures is presented. The structure is composed of a set of microactuators which contains a rigid plate with two supporting composite beams. A model is developed to describe analytically the relationship between the force and the deflection of microactuators by electrostatic measurements, and the elastic modulus of multi-layered beams with different widths are evaluated. FEM simulations are implemented to validate the accuracy of the relationship between the on-load voltage and the capacitance between the microactuator and the electrode on the substrate. Test structures are fabricated using CMOS-MEMS process and experiments are to be carried out soon.