CMOS MEMS 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

Design and Characterization of a Frequency- and Amplitude-Controlled CMOS MEMS Resonant Scanning Mirror

Design and Characterization of a Frequency- and Amplitude-Controlled CMOS MEMS Resonant Scanning Mirror

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.

A Low-Power Sensing System of VEGF Concentration With Noise Reduction Using Subsampling Technique for Cancer Diagnosis

This paper presents a monolithic low-power sensing system for early cancer detection. The system uses a CMOS MEMS capacitive transducer with a gold interdigitated electrode (IDE) and DNA aptamers to sense the concentration of vascular endothelial growth factor (VEGF). When the DNA aptamer is immobilized with the VEGF sensor, it generates an electric double-layer capacitance. The low-noise front-end circuits amplify this capacitance change and convert the signal into the frequency domain. To solve the wide input dynamic range and reduce power consumption, a two-step time-to-digital converter (TDC) is utilized. The proposed sub-sampling (SS) technique provides a higher conversion gain to reject noise interference and overcome the increase in noise floor introduced from the decoder due to lower supply voltage. The sub-sampling delay-locked loop (SSDLL), combined with the calibration circuit, enhances TDC linearity and noise performance while preventing calibration noise from degrading conversion accuracy. Finally, the time-based information is converted into digital codes with high power efficiency for early cancer analysis. The system is fabricated in TSMC 0.35 μm MEMS CMOS process with electroplated gold. Measurement results show that the power consumption of the readout circuit and the overall system is only 18 μW and 60.65 μW, respectively. The proposed system improves jitter by 49% and achieves 0.725 mV/pg-mL sensitivity.

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.

Miniaturized thermal acoustic gas sensor based on a CMOS microhotplate and MEMS microphone

We present a miniaturised thermal acoustic gas sensor, fabricated using a CMOS microhotplate and MEMS microphone. The sensing mechanism is based on the detection of changes in the thermal acoustic conversion efficiency which is dependent on the physical properties of the gas. An active sensing element, consisting of a MEMS microphone, is used to detect the target gas while a reference element is used for acoustic noise compensation. Compared to current photoacoustic gas sensors, our sensor requires neither the use of gas-encapsulated microphones, nor that of optical filters. In addition, it has all the benefits of CMOS technology, including production scalability, low cost and miniaturization. Here we demonstrate its application for CO_2 gas detection. The sensor could be used for gas leak detection, for example, in an industrial plant.

A Wafer-Level Packaged CMOS MEMS Pirani Vacuum Gauge

In this article, we report a wafer-level packaged Pirani vacuum gauge using the proprietary InvenSense CMOS MEMS technology. The micro Pirani vacuum gauge features three serpentine-shaped molybdenum thermistors on the suspended silicon-on-insulator (SOI) bridges, while the wiring gap of each serpentine-shaped silicon microbridge is 1.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${ {\mu }}\text{m}$ </tex-math></inline-formula> . For the vacuum range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 10^{-{4}}$ </tex-math></inline-formula> –760 Torr, the CMOS MEMS Pirani gauge configured with a constant temperature interface circuit achieves a sensitivity of 0.414 V/Torr in a very fine vacuum regime, while its heating power is less than 21.3 mW. Moreover, the measured output of the micro Pirani gauge shows good agreement with a semi-empirical model, while the model predicts that the proposed Pirani gauge can measure a vacuum pressure as low as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.6\times 10^{-{4}}$ </tex-math></inline-formula> Torr. The performance achieved by this Pirani vacuum gauge combined with its high level of integration makes it a promising Internet of Things (IoT) sensing node for vacuum monitoring in the industry.

A Reliable Liquid-Based CMOS MEMS Micro Thermal Convective Accelerometer With Enhanced Sensitivity and Limit of Detection

In this paper, a liquid-based micro thermal convective accelerometer (MTCA) is optimized by the Rayleigh number ( Ra ) based compact model and fabricated using the $0.35\mu $ m CMOS MEMS technology. To achieve water-proof performance, the conformal Parylene C coating was adopted as the isolation layer with the accelerated life-testing results of a 9-year-lifetime for liquid-based MTCA. Then, the device performance was characterized considering sensitivity, response time, and noise. Both the theoretical and experimental results demonstrated that fluid with a larger Ra number can provide better performance for the MTCA. More significantly, Ra based model showed its advantage to make a more accurate prediction than the simple linear model to select suitable fluid to enhance the sensitivity and balance the linear range of the device. Accordingly, an alcohol-based MTCA was achieved with a two-order-of magnitude increase in sensitivity (43.8 mV/g) and one-order-of-magnitude decrease in the limit of detection (LOD) ( $61.9~\mu \text{g}$ ) compared with the air-based MTCA. [2021-0092]

CMOS-MEMS VOC sensors functionalized via inkjet polymer deposition for high-sensitivity acetone detection.

CMOS-MEMS microresonators have become excellent candidates for developing portable chemical VOC sensing systems thanks to their extremely large mass sensitivity, extraordinary miniaturization capabilities, and on-chip integration with CMOS circuitry to operate as a self-sustained oscillator. This paper presents two 4-anchored MEMS plate resonators, with a resonance frequency of 2.2 MHz and 380 kHz, fabricated together with the required circuitry using a commercial 0.35 μm CMOS technology and then coated with poly-4-vinylheduorocumyl alcohol (P4V) via inkjet deposition. Such P4V constitutes a functionalization layer for specific acetone detection as a key step in the development of an integrated device for non-invasive diabetes diagnosis through exhaled human breath. The coated sensor system has been proven to increase the acetone injection response by 6-times compared to the uncoated platform and shows a cross-sensitivity to butane of 1 : 11. Experimental data show an acetone sensitivity of -0.012 ppm Hz-1 in the best case that, together with a measured frequency Allan deviation of 0.32 ppm, provides an expected limit of detection as low as 20 ppb of acetone. Additionally, this work presents an alternative resonator design with folded flexure anchors that provide a drastic reduction of the sensor temperature sensitivity and mitigate the impact of a fluid flow inherent to the calibration system.

Integrated Predicted Mean Vote Sensing System Using MEMS Multi-Sensors for Smart HVAC Systems

In this article, we report a predicted mean vote (PMV) index based micro Human Thermal Comfort Sensing (HTCS) system with multiple MEMS sensors. The system consists of a wireless multi-sensor (CMOS MEMS air velocity, MEMS relative humidity (RH) and MEMS air temperature) module to measure three environmental parameters and a smartphone App with a novel motion analytics algorithm (for estimation of metabolic rate) and personal factors (clothing insulation) input. While the majority of the reported HTCS systems are bulky and takes only environmental parameters into consideration, the developed system utilizes MEMS technology for sensors’ fabrication and measures the essential environmental and human factors involved to compute human thermal comfort. Furthermore, the developed HTCS system shows much better accuracy (±0.13) than its commercial and reported counterparts (±0.17 to ±0.4). Moreover, the packaged HTCS system is placed in a testing room to monitor the PMV. The experimental results indicated that our micro PMV-based HTCS system is promising for smart HVAC system integration in the era of the Internet of Things.

A CMOS MEMS Thermal Flow Sensor for Gas and Liquid With Parylene-C Coating

This brief presents a self-heated thermoresistive flow (SHTF) sensor for both gas and liquid with Parylene-C coating using a 0.35- $ \mu \text{m}$ CMOS MEMS technology. For N2 flow, the developed SHTF sensor can achieve the highest normalized sensitivity ( $S^{ \ast }{ =}\,\, {S}_{c} / {P}$ ) of 171 mV/(m/s)/W with its power consumption ${P}$ of less than 18.3 mW. Meanwhile, the SHTF sensor has an accuracy of ±0.04 m/s within the linear flow range of 0–2.5 m/s, which is capable of indoor airflow measurement even in humid environment. For water flow, the SHTF sensor gains a sensitivity ${S}_{W} ^{ \ast }$ of 6.42 V/(m/s)/W with the configured calorimetric setup, while its sensitivity increased by more than 4X as it assigned as anemometric for a Nusselt number Nu of 0–9. Therefore, this highly sensitive CMOS MEMS SHTF sensor with the coated Parylene-C will be a very useful device for both gas and liquid flow measurement in heating, ventilation, and air conditioning (HVAC) and microfluidic applications.

Portable Real-Time Detection of Pb(II) Using a CMOS MEMS-Based Nanomechanical Sensing Array Modified with PEDOT:PSS.

Detecting the concentration of Pb2+ ions is important for monitoring the quality of water due to it can become a health threat as being in certain level. In this study, we report a nanomechanical Pb2+ sensor by employing the complementary metal-oxide-semiconductor microelectromechanical system (CMOS MEMS)-based piezoresistive microcantilevers coated with PEDOT:PSS sensing layers. Upon reaction with Pb2+, the PEDOT:PSS layer was oxidized which induced the surface stress change resulted in a subsequent bending of the microcantilever with the signal response of relative resistance change. This sensing platform has the advantages of being mass-produced, miniaturized, and portable. The sensor exhibited its sensitivity to Pb2+ concentrations in a linear range of 0.01–1000 ppm, and the limit of detection was 5 ppb. Moreover, the sensor showed the specificity to Pb2+, required a small sample volume and was easy to operate. Therefore, the proposed analytical method described here may be a sensitive, cost-effective and portable sensing tool for on-site water quality measurement and pollution detection.

CMOS MEMS Thermoelectric Infrared Sensor With Plasmonic Metamaterial Absorber for Selective Wavelength Absorption and Responsivity Enhancement

This study demonstrates the integration of thermoelectric type MEMS infrared (IR) sensor with plasmonic metamaterial absorber (PMA) through a standard CMOS process platform to improve the responsivity of MEMS IR sensor in a specific range of wavelength. Based on an existing thermoelectric IR sensor with the serpentine film structure, the proposed device further combines with a Metal-Insulator-Metal (MIM) type PMA. The absorber consists of a top antenna layer, a middle dielectric spacer, and a bottom reflector, and the metal and dielectric films in the standard CMOS process are exploited in this study to implement the MIM design. The advantage of narrow linewidth in CMOS process can meet the need of critical dimensions for MIM antennas. The absorption wavelength can be adjusted by varying the pattern and dimension of antennas. The MIM PMAs are designed in the coupling regime, and hence the shifting of absorbed wavelength caused by the variation of antenna dimensions from fabrication can be prevented. The feasibility of the presented MIM PMA is demonstrated by simulations and experiments. The absorption spectra measured by FTIR show the capability of proposed MIM PMAs in extending the absorption range of far-infrared. Measurement results also indicate that under the same sensor footprint and the equal number of thermocouples, the device integrated with the proposed MIM PMA has a 20 percent improvement in responsivity as well as detectivity.

Sidewall Metallization on CMOS MEMS by Platinum ALD Patterning

Patterned atomic layer deposition (ALD) that selectively coats sidewalls with platinum (Pt) is developed to improve performance on CMOS MEMS devices. The proposed fabrication process is the first, to our knowledge, to pattern metal ALD on high-aspect-ratio MEMS sidewalls. A reflow step for the lift-off resist is introduced to increase yield by solving stringer issues. Sidewall metallization enables higher sensitivity on capacitive sensors and eliminates dielectric charging. A Pt-coated resonator oscillator and a capacitive accelerometer are demonstrated as examples, showing the successful process results. The measurement on a Pt-coated resonator oscillator indicates much higher stability than with the original dielectric sidewalls. This metal sidewall coating also has potential for other CMOS MEMS devices, such as switches. [2020-0178]

Simultaneous Flow and Thermal Conductivity Sensing on a Single Chip Using Artificial Neural Networks

A thin-film CMOS MEMS thermal sensor has been designed, fabricated and tested with the addition of through-membrane isolating holes. These holes have been shown to enhance the discrimination towards gases with differing thermal conductivity in the presence of flow. Using three on-membrane resistors as inputs, linear statistical methods alongside Artificial Neural Network pattern recognition techniques have been investigated for decoupling the two parameters of thermal conductivity and flow rate using a single sensor. In addition to this, the addition of the membrane holes increases the sensitivity towards flow rate by 10 times and the sensitivity towards thermal conductivity by 2 times. This sensor design coupled with well-known post-processing techniques will enable a new generation of multi-parameter sensing solutions.

High Sensitivity and Wide Dynamic Range Thermoresistive Micro Calorimetric Flow Sensor With CMOS MEMS Technology

In this paper, a thin film based Thermoresistive Micro Calorimetric Flow (TMCF) sensor by using a $0.35~\mu \text{m}$ 2P4M CMOS MEMS technology is designed, fabricated and tested. The developed $1.6~\mu \text{m}$ thick thin film CMOS TMCF sensor shows a maximum normalized sensitivity of 103 mV/(m/s)/mW with respect to the input heating power and a wide dynamic flow range of 0 ~ 19.4 m/s. The high sensitivity and wide dynamic range achieved by our CMOS MEMS flow sensor enable its deployment as a promising sensing node for HVAC application in the smart energy-efficient building (EeB). Moreover, a new one-dimensional (1D) analytical sensor model that considers the three-dimensional (3D) heat loss via the end of the thin film is proposed. The new 1D model can successfully capture the thin film based TMCF sensor’s response, and its prediction results show a good agreement with the experimental study. Therefore, this new 1D model will be a useful design tool for the development of a high-performance TMCF sensor with a greatly reduced footprint.

CMOS MEMS Thermal Flow Sensor With Enhanced Sensitivity for Heating, Ventilation, and Air Conditioning Application

In this article, by using 0.35- μ m two-polysilicon four-metal CMOS MEMS technology, a thermoresistive micro calorimetric flow (TMCF) sensor with two packaging designs is systematically investigated: Open-space (O-type) and probe-with-channel (P-type) designs. In comparison with the O-type design, the P-type sensor shows an 80% enhanced sensitivity with a relieved tilt angle effect on the mainstream airflow detection. Accordingly, the P-type packaged flow sensor for HVAC gains a prominent normalized sensitivity ( S* ) of 228 μV/(m/s)/mW, while also having a low power consumption ( P ) of less than 4.2 mW. Moreover, within the linear range of –2 to 2 m/s, an accuracy of ±0.05 m/s is achieved, thus enabling this robust flow sensor (repeatability <0.2%) for indoor airflow measurements even in a variable ambient environment. Furthermore, the proposed P-type TMCF sensor and its wireless multisensor module are applied for the development of personalized ventilation and the monitoring of predicted mean vote, both of which confirm the functionality of the developed sensor for indoor airflow measurements in the HVAC system.

Two-Dimensional CMOS MEMS Thermal Flow Sensor With High Sensitivity and Improved Accuracy

In this paper, we report a two-dimensional (2D) Thermoresistive Micro Calorimetric Flow (TMCF) sensor by using a $0.35~\mu \text{m}$ 2P4M CMOS MEMS technology. For the airflow, the fabricated and the open-space packaged 2D flow sensor system achieved the highest normalized sensitivity of 32 mV/W/(m/s) with respect to input heating power and gain. To overcome the sensor output drifting issue due to the locally redistributed fluid flow near the bonding wires, a digital signal conditioning algorithm using the inverse distance weighting (IDW) method, instead of the conventional fitting method with sine and cosine function, was proposed. Accordingly, the calibrated 2D flow sensor showed an improved velocity accuracy of ±4% and the angle accuracy of ±3° for an input airflow from 0 to 20 m/s. Therefore, the developed highly sensitive 2D TMCF sensor will be a promising device for the airflow measurement in the smart buildings and the meteorological monitoring system. [2019-0259]

Active Thermoelectric Vacuum Sensor Based on Frequency Modulation.

This paper introduces a thermoelectric-type sensor with a built-in heater as an alternative approach to the measurement of vacuum pressure based on frequency modulation. The proposed sensor is fabricated using the TSMC (Taiwan Semiconductor Manufacturing Company, Hsinchu, Taiwan) 0.35 μm complementary metal-oxide-semiconductor-microelectro-mechanical systems (CMOS–MEMS) process with thermocouples positioned central-symmetrically. The proposed frequency modulation technique involves locking the sensor output signal at a given frequency using a phase-lock-loop (PLL) amplifier to increase the signal-to-noise ratio (SNR) and thereby enhance the sensitivity of vacuum measurements. An improved first harmonic signal detection based on asymmetrical applied heating gives a precise measurement. Following calibration, the output voltage is in good agreement with the calibration values, resulting in an error of 0.25% under pressures between 0.1–10 Torr.

A CMOS-MEMS Thermoresistive Micro Calorimetric Flow Sensor With Temperature Compensation

In this paper, we propose a new 1D thermoresistive micro calorimetric flow (TMCF) sensor model for moist airflow with the temperature-dependent thermophysical properties. The 1D model and the corresponding proposed equivalent circuit model enable rapid design optimization of an ambient temperature-compensated TMCF (T2MCF) sensor integrated with the interface circuit by using a commercial 0.35- $\mu \text{m}$ 2P4M CMOS MEMS technology. The fabricated sensor shows a prominent sensitivity of 0.543 V/(m/s) and a low power consumption of less than 2.8 mW. Moreover, in comparison with the large drifting of 49% for the uncompensated TMCF sensor, the T2MCF sensor’s output has an ultralow drifting of 0.5% with the ambient temperature variation of 22°C~48°C. Therefore, this robust T2MCF sensor can be a promising Internet of Things (IoT) for smart energy-efficient buildings. [2018-0241]