Size effect on microscale single-phase flow and heat transfer

Size effect on single-phase channel flow and heat transfer at microscale

Microelectromechanical systems sensors have been intensively developed utilizing various physical concepts, such as piezoresistive, piezoelectric, and thermoresistive effects. Among these sensing concepts, the thermoresistive effect is of interest for a wide range of thermal sensors and devices, thanks to its simplicity in implementation and high sensitivity. The effect of temperature on the electrical resistance of some metals and semiconductors has been thoroughly investigated, leading to the significant growth and successful demonstration of thermal-based sensors, such as temperature sensors, convective accelerometers and gyroscopes, and thermal flow sensors. In this paper, we review the fundamentals of the thermoresistive effect in metals and semiconductors. We also discuss the influence of design and fabrication parameters on the thermoresistive sensitivity. This paper includes several desirable features of thermoresistive sensors and recent developments in these sensors are summarized. This review provides insights into how it is affected by various parameters, and useful guidance for industrial designers in terms of high sensitivity and linearity and fast response. [2017-0022]

Thermoresistive Effect for Advanced Thermal Sensors: Fundamentals, Design Considerations, and Applications

This paper addresses the design of CMOS thermal accelerometers. A test-chip including the sensor and a signal conditioning circuit has been designed, fabricated and characterized. The fabricated prototype exhibits good performance: the measured resolution is better than 30 mg (equivalent to 1.7° in inclination) with a sensitivity of 375 mV/g. The bandwidth is around 15 Hz. This test-chip is used to improve the modelling of heat transfer phenomenon for this family of devices. FEM is successfully used as a first modelling approach. Although thermal convective accelerometers have already been reported and even commercialised, few information regarding behavioural modelling, optimization issues, and their integration on CMOS technology is today available. In particular, no information about response time modelling was reported in the literature. Thanks to experimental results and FEM simulations, we provide in this study information concerning the integration of convection heat transfer accelerometers on CMOS. In addition, the effects of the packaging (i.e. the top and bottom cavities) on both the static sensitivity and the dynamic response of the sensor have been investigated.

/pdf/experimental-and-finite-element-study-of-convective-4jibs1nl4k.pdf

Experimental and finite-element study of convective accelerometer on CMOS

In the present work, the design of a micromachined thermal accelerometer based on convection effect was studied. The accelerometer sensitivity and especially the frequency response have been experimentally and numerically studied with low cavity volume. Although this type of sensor has already been intensively examined, few information concerning the frequency response modeling is currently available. In particular, no experimental result about frequency response for low volume and their variation according to the external temperature variation was reported in the literature. In certain particular condition, we assumed that a bandwidth of 120 Hz at −3 dB has been measured. By using numerical resolution of fluid dynamics equations with the computational fluid dynamics (CFD) software package Fluent V6.2 and a simple model based on thermo-conduction, a good accordance with the experimental results has been demonstrated. So, the effects of these two parameters like the volume and the external temperature variation on the thermal accelerometer response have been theoretically, experimentally and numerically investigated.

Studies and optimization of the frequency response of a micromachined thermal accelerometer

Miniaturization, low cost and high performance of accelerometers have been the topic of extensive research. A kind of convective micromachined accelerometer without proof mass is described in this paper. It consists of a microheater and two temperature sensors which measure the temperature difference between two sides of the microheater caused by the effect of acceleration on free convection. The optimization consideration is conducted before fabrication; some key factors, heater size and power, cavity size, distance between the heater and the sensor and the working medium, are considered. The test for the optimized device shows that the linearity error is smaller than 0.35% under tilt conditions of natural gravity and smaller than 2% under acceleration to 10 g (g = 9.81 m s-2). A sensitivity of 600 µV g-1 is measured for operating power of 87 mW, the response frequency is about 75 Hz and the corresponding noise equivalent acceleration is approximately 1 mg Hz-1/2 at 25 Hz. The dependence of the sensitivity on the heating power is a nearly linear function and the resolution increases with heating power increasing.

https://iopscience.iop.org/article/10.1088/0960-1317/11/5/309/pdf

Y J Yang

Papers

An optimized micromachined convective accelerometer with no proof mass