Thermoresistive Micro Calorimetric Flow Sensor Research Articles

A high-sensitivity calorimetric digital flow meter for respiratory monitoring and proximal flow measurement in neonatal ventilation

In this paper, a high-sensitivity digital flow meter, featuring a low-power Thermo-resistive Micro Calorimetric Flow (TMCF) sensor fabricated by CMOS-MEMS technology, is presented for respiratory monitoring and neonatal ventilator-assisted ventilation. The packaging of the TMCF sensor has been meticulously optimized to achieve a 1.5-fold increase in sensitivity, resulting in a high sensitivity of 76.5 mV/SLM in the linear range of −7.5SLM to 7.5SLM, and its heating power is only 2.23 mW. The developed digital flow meter is quantized into a 14 bit output within the flow measurement range of −40SLM to 40SLM, providing a high resolution down to 0.005SLM. With a remarkable response time of less than 11.5 ms, corresponding to a bandwidth of 13.8 Hz, and equipped with a 2 kHz data update rate, our proposed digital flow meter excels in capturing abrupt changes in breathing and high-frequency respiratory signals. Furthermore, boasting a noise level below 0.0025SLM, the sensor system demonstrates the capability to identify subtle variations in respiratory flow. Based on its outstanding performance, the high-sensitivity digital flow meter effectively identifies simulated abnormal respiratory patterns, including apnea, polypnea, and hypopnea, and successfully performs closed-loop ventilation measurements for neonates on a ventilator. Therefore, it holds promising potential as a crucial sensing component with high precision, high sensitivity, and low power consumption in respiratory monitoring and neonatal ventilation therapy.

A Fast-Response Breathing Monitoring System for Human Respiration Disease Detection

This paper presents a sensing system for the real-time monitoring of human respiration. The system is equipped with a fast response thermoresistive micro calorimetric flow (TMCF) sensor and a dedicated data processing algorithm. The TMCF sensor is designed with a proposed nonlinear sensor model and fabricated in a CMOS compatible process, which obtains a high sensitivity of 114 mV/SLM and a fast response time of less than 6 ms. By using this high-performance micro flow sensor and its proprietary data processing algorithm, critical human respiration information including respiratory rate (RR) and minute ventilation (MV) can be easily obtained. The proposed sensing system achieves a very small mean absolute error (MAE) of less than 2.7 mHz for RR, and the extracted MV is also in good agreement with the commonly reported value of 4 - 6 L/min. In addition, benefiting from the very short time constant of the developed TMCF sensor, the proposed sensing system can successfully distinguish different respiratory diseases, such as apnea, hypopnea, polypnea, etc. Therefore, this proposed human respiration monitoring system will be a promising sensing technology for respiration diagnosis in medical applications.

Bidirectional CMOS-MEMS Airflow Sensor With Sub-mW Power Consumption and High Sensitivity

This article presents a bidirectional thermoresistive micro calorimetric flow (TMCF) sensor implemented by a 0.18- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m complementary metal–oxide–semiconductor microelectromechanical systems (CMOS-MEMS) technology, while the sensor thickness is thinned to 2.7 μm through an in-house developed MEMS fabrication process. For the bidirectional airflow of −6 to 6 m/s, the TMCF sensor achieves the highest sensitivity of 453 mV/(m/s), and its highest normalized sensitivity with respect to the signal amplification gain (gain = 250) and the input heating power (1.58–1.72 mW) is 1150 mV/(m/s)/W. By reducing the heating power to the sub-mW of <220 μW, the TMCF sensor can still give a remarkable sensitivity of 87.4 mV/(m/s). In addition, the developed TMCF sensor has an intrinsic minimum detectable flow velocity of 99 μm/s and a response time of 4.8 ms. The performance achieved by this flow sensor enables accurate indoor airflow measurements even when dealing with the extremely low-speed flow (<0.05 m/s). Furthermore, the high-performance TMCF sensor is applied for remote human motion detection, where different walking speeds and moving patterns of the occupants can be captured. Therefore, this developed CMOS-MEMS sensor will not only be a promising flow sensing node in the HVAC system, but also potentially be used for the nonvisible and private occupant counting in buildings/rooms.

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]

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]

A Three-Dimensional Integrated Micro Calorimetric Flow Sensor in CMOS MEMS Technology

This article presents a 3-D integrated molybdenum (Mo) thermoresistive microcalorimetric flow sensor in a 0.18-μm CMOS MEMS technology. The sensor consists of a MEMS structure which is fabricated inside a sealed microchannel and a constant temperature control circuit implemented on the CMOS wafer. The MEMS structure and the CMOS circuit are 3-D integrated at the wafer level. For the N2 gas flow, the proposed flow sensor achieves a high sensitivity of 0.71 mV/(m/s) and a wide bidirectional detection ability of −26–26 m/s. Moreover, an equivalent circuit model is proposed in this article, which depicts the nonlinear output/overheated temperature ( V out/Δ T h) sensor response to the input gas flow. This model would be an efficient tool for the design and optimization of high-performance system-on-chip calorimetric flow sensors.

Systematic study of packaging designs on the performance of CMOS thermoresistive micro calorimetric flow sensors

We systematically study the effect of two packaging configurations for the CMOS thermoresistive micro calorimetric flow (TMCF) sensors: S-type with the sensor chip protrusion-mounted on the flow channel wall and E-type with the sensor chip flush-mounted on the flow channel wall. Although the experimental results indicated that the sensitivity of the S-type was increased by more than 30%; the corresponding flow range as compared to the E-type was dramatically reduced by 60% from 0–11 m s−1 to 0–4.5 m s−1. Comprehensive 2D CFD simulation and in-house developed 3D numerical simulations based on the gas-kinetic scheme were applied to study the flow separation of these two packaging designs with the major parameters. Indeed, the S-type design with the large protrusion would change the local convective heat transfer of the TMCF sensor and dramatically decrease the sensors’ performance. In addition, parametric CFD simulations of the packaging designs provide inspiration to propose a novel general flow regime map (FRM), i.e. normalized protrusion d* versus reduced chip Reynolds number Re*, where the critical boundary curve for the flow separation of TMCF sensors was determined at different channel aspect ratios. The proposed FRM can be a useful guideline for the packaging design and manufacturing of different micro thermal flow sensors.

Theoretical and Experimental Investigations of Thermoresistive Micro Calorimetric Flow Sensors Fabricated by CMOS MEMS Technology

A general 1-D model was presented to predict the characteristics of CMOS thermoresistive micro calorimetric flow (TMCF) sensor with two types of packaging, i.e., open-space type and channel type, for both gases and liquids. The 1-D model was first validated by a numerical computational fluid dynamics (CFD) model and was subsequently normalized for different fluids flow. Notably, the model proposed by Nguyen and Dotzel is a special case of our 1-D model. The normalized output of TMCF sensor is a function of normalized input parameters of Reynolds number Re and Prandtl number Pr. The scaling analysis of the sensor output, sensitivity, and power consumption was performed to optimize the design of TMCF sensors in terms of key design parameters, including the thin film thickness, the height of bottom cavity, and so on. Accordingly, three pairs of TMCF sensors were designed and fabricated by using a 0.35 $\mu \text{m}$ 2P4M CMOS microelectromechanical systems technology. The fabricated sensors showed a normalized sensitivity of 230 mV/(m/s)/mW for nitrogen gas flow, which was two orders of magnitude higher than the previous CMOS flow sensors. Therefore, the proposed 1-D model is a promising tool for the sensor’s system-level design with the on-chip microelectronics for the Internet of Things. [2016-0098]