Resonant Thermal Sensor Research Articles

Microfabricated Temperature-Sensing Devices Using a Microfluidic Chip for Biological Applications

Microelectromechanical systems (MEMS) and micrototal analysis systems (μTAS) have been developed using microfabrication technologies. As MEMS and μTAS contribute to smaller, higher-performance, less expensive, and integrated sensing techniques, they have been applied in many fields. In this paper, we focus on microfabricated thermal detection devices, including a microthermistor fabricated using vanadium oxide (VOx) and a resonant thermal sensor integrated into a microfluidic chip, and we present the research work we have done into biological applications, applications using a unique material and detection method for liquid samples. The VOx thermistor, which has a high temperature coefficient of resistance at –1.3%/K, is mounted onto a thermally insulated membrane in the microfluidic chip. This device is used to detect glucose and cholesterol concentrations in solutions. The resonant thermal sensor is another candidate for obtaining highly sensitive thermal measurements; however, this sensor is difficult to use with liquids because of vibration damping and thermal loss. To solve these problems, we propose a partial vacuum packaging system for the sensor in the microfluidic chip. This technique, which involves silicon resonators, was used to successfully detect the heat from a single brown fat cell. Moreover, the possibility of using a VOx resonant thermal sensor is discussed. The future prospects for MEMS and automation technology are described, with a focus on the Internet of Things/big data for medical and healthcare applications.

Geometry dependence of temperature coefficient of resonant frequency in highly sensitive resonant thermal sensors

In this paper, the geometry dependence of the temperature coefficient of resonant frequency (TCRF) is investigated and compared with a theoretical thermal stress change using Si mechanical microresonators. The used resonators have Y, T, I (conventional double-supported type) and arrow shapes, and in each shape the resonant frequency change of the resonator is measured in relation to changes in the amount of heat input to the resonator. The change trend in the experimental resonant frequency and the theoretical thermal stress in changing the temperature are consist. The TCRF in each resonator is Y: −653, T: −162, I: −417, and the arrow is 174 ppm/K. These absolute values are much higher than those of conventional cantilevered Si resonators (−34.9 ppm/K). In addition, the frequency fluctuations based on Allan deviation are experimentally evaluated considering the theoretical thermal fluctuation noise. It is considered that use of this technique to improve the TCRF of resonators by changing the geometry has the possibility of creating a sensor with highly sensitive thermal detection.

Temperature-depended mechanical properties of microfabricated vanadium oxide mechanical resonators for thermal sensing

This study describes our newly fabricated resonant thermal sensors based on vanadium oxide and investigates the temperature dependences of their resonant frequencies and Q factor. The suspended vanadium oxide resonators are microfabricated using Au or SiO2 as the sacrificial layer. The resonant frequency of the fabricated vanadium oxide resonators linearly varies with temperature, and the value of temperature coefficient of the resonant frequency is −1308 ppm/K in the range of 20–100 °C. The averaged Q factor in this range was 540. The temperature and thermal resolution of the vanadium oxide resonator are estimated as 1.7 mK/ and 4.3 nW/, respectively, which are higher than those of a Si resonator having similar dimensions and under similar conditions. Therefore, the feasibility that vanadium oxide is a promising material for resonant thermal sensors is indicated.

Thermal expansion mismatch resonant infrared sensor and array

A resonant infrared thermal sensor with high sensitivity, whose sensing element is a bimaterial structure with thermal expansion mismatch effect, is presented. The sensor detects infrared radiation by means of tracking the change in resonance frequency of the bimaterial structure with temperature attributed to the infrared radiation from targets. The bimaterial structure is able to amplify the change in resonance frequency compared with a single material structure for a certain mode of vibration. In accordance with the vibration theory and the design principle of an infrared thermal detector, the resonant sensor, which can be arranged in an array, is designed. The simulation results, by using finite element analysis, demonstrate that the dependence of resonance frequency on temperature of the designed structure achieves 1 Hz/10 mK . An array of 6×6 resonant thermal sensors is fabricated by using microelectronics processes that are compatible with integrated circuit fabrication technology. The frequency variation corresponding to the temperature shift is obtained by electrical measurement.

(Invited) Si-Based Micro-Nanomechanics for Ultimate Sensing

Recent silicon micro- and nano-fabrication techniques have been well-developed and their application fields are extended. Among them Si micro-nanomechanical systems have been developed for various applications including sensors and actuators. We developed Si micro-nanomechanical resonant sensors for ultimate sensing. One of advantages of silicon material is the compatibility with integrated circuits. Also, Si micro-nanoresonators show a high quality factors by thermal treatment in vacuum [1]. By miniaturization of the resonators, the sensitivity to mass, force, and heat increases due to scaling merit. Therefore, much effort has been made for developing micro/nano-mechanical sensors for such applications. Magnetic resonance force microscopy is powerful method for visualization of spins in a sample, where a resonant sensor with a magnet is used to detect the flip of magnetic spins due to magnetic resonance [2-4]. From the resonant frequency or vibration amplitude of the resonator, magnetic force between the magnet and spins in a sample can be detected. From scaling low, higher sensitivity is expected using a narrower and longer probe structure, which means that nanowired structure is effective to obtain high sensitivity. Using a silicon insulater wafer, a Si nanowire probe with a micro magnet (Nd-Fe-B) and a Si mirror is fabricated. The nanowire Si structure is fabricated by conventional microfabrication using electron beam lithography. In order to increase the Q factor, the fabricated Si resonator is annealed at H2/N2 atmosphere. The vibration is measured using a fiber-optic interferometer in a vacuum chamber at room temperature [4]. The achieved detectable minimum force was at an order of 10-17 N, which is estimated from thermomechanical noise signal. Mapping of electron resonance is demonstrated on a small particle of PVBPT (Poly-10-(4-vinylbenzyl)-10H-phenothiazine). Resonant heat sensor are developed and applied to a calorimeter for the detection of heat from a brown fat cell [5]. The measurement principle relies on the resonant frequency tracking of a Si resonator in temperature variation due to heat from a sample, and heat is conducted from the sample in water to the Si resonator in vacuum via a Si heat guide. A heat loss to surrounding and a dumping in water can be reduced by placing the resonant thermal sensor in vacuum. The fabricated resonant thermal sensor shows 1.6 mK of the temperature resolution, and 6.2 pJ of the detectable minimum heat. The heat from the single cell is detected in cases without any stimulation and with stimulation. As the results, pulsed heat production and continuous heat production are observed, respectively.

(Invited) Si-Based Micro-Nanomechanics for Ultimate Sensing

Resonant sensors for ultimate sensing are developed. By scaling down, the sensitivity of a magnetic resonance force microscopy probe is improved, and three-dimensional imaging of radical density in a poly-10-(4-vinylbenzyl)-10H-phenothiazine particle is demonstrated at room temperature. Also resonant thermal sensor with a microchannel is developed and applied to detect heat from a single brawn fat cell.

Thermal Sensor Probe with a Si Resonator in a Cavity for Thermal Insulation

A thermal sensor probe with a Si resonator in a cavity for thermal insulation was designed and fabricated to measure a heat from fluidic samples in an atmosphere. The resonant thermal sensor was isolated in a cavity in a probe to decrease a vibration damping and a heat loss to surrounding environments, which increased the thermal sensitivity. The heat from the sample at the probe tip was conducted via a heat guide into the resonator in the cavity. Characteristics of the sensor probe were evaluated in terms of a quality factor, a temperature coefficient of the resonant frequency of the resonator, and a frequency stability. Its thermal resolution was 0.3 °C. The measurement of the D-glucose concentration in a droplet was demonstrated from its temperature changes. Our sensor probe could access specific samples on a two-dimensional space and has a feasibility to accomplish highly sensitive thermal measurements without any vacuum equipment.

J026032 生体試料のための真空隔離型共振熱センサ([J026-03]細胞および分子のマイクロ・ナノスケール解析(3))

We have developed a resonant thermal sensor system for biological samples. The measurement principle relies on the resonant frequency shift of the resonant thermal sensor due to the temperature change. Brown fat cells, which are frequently used for metabolism researches, attract our interests to solve obesity, metabolic syndrome, and so on. To measure its thermal characteristics in single cell level, a heat loss to surrounding environments and a vibration damping should be solved when resonant thermal sensors are immersed in water. To solve these problems and realize highly sensitive thermal measurements, a resonant thermal sensor was partly placed in vacuum, and another end was in microchannel as a sample stage in a microfluidic chip. They were connected physically and thermally by a heat guide. The heat from the cell is conducted to the sensor via the heat guide, and measured. A fabricated device was evaluated by using laser Doppler vibrometer. The thermal resolution of the device was 5.2 pJ. The single brown fat cell was set on the sample stage, and generated heats were measured with and without stimulation. With the stimulation, pulsed heats were observed, which have not observed in bulk measurements. With the stimulation, gradual and long heat generations were caused similarly with bulk measurements. We have succeeded in detecting the heat from single brown fat cell by using the fabricated device.

Thermal imaging with tapping mode using a bimetal oscillator formed at the end of a cantilever

Thermal detection based on the thermal shift of the resonant frequency of a bimetal resonator (Al/Si) is presented and demonstrated. The bimetal oscillator with a tip is fabricated at the end of a commercial silicon cantilever. The bimetal oscillator and the silicon cantilever have a resonance frequency of 441 and 91 kHz, respectively, and the measured temperature coefficients of the resonant frequency are -127x10(-6)/K and -115x10(-6)/K, respectively. It is demonstrated that self-oscillated resonant frequency of the bimetal oscillator changes in response to heat from a microheat source. Simultaneous measurements of topography and temperature profile with the temperature resolution of 0.12 K on a glass substrate heated using a thin chromium film microheater are successfully demonstrated. These results show potential abilities of the mechanical resonant thermal sensor.