Fabrication and Characterization of CMOS-MEMS Thermoelectric Micro Generators

This work presents a thermoelectric micro generator fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and the post-CMOS process. The micro generator is composed of 24 thermocouples in series. Each thermocouple is constructed by p-type and n-type polysilicon strips. The output power of the generator depends on the temperature difference between the hot and cold parts in the thermocouples. In order to prevent heat-receiving in the cold part in the thermocouples, the cold part is covered with a silicon dioxide layer with low thermal conductivity to insulate the heat source. The hot part of the thermocouples is suspended and connected to an aluminum plate, to increases the heat-receiving area in the hot part. The generator requires a post-CMOS process to release the suspended structures. The post-CMOS process uses an anisotropic dry etching to remove the oxide sacrificial layer and an isotropic dry etching to etch the silicon substrate. Experimental results show that the micro generator has an output voltage of 67 μV at the temperature difference of 1 K

Titanium Dioxide Nanoparticle Humidity Microsensors Integrated with Circuitry on-a-Chip

A humidity microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm CMOS (complementary metal oxide semiconductor) process was presented. The integrated sensor chip consists of a humidity sensor and a readout circuit. The humidity sensor is composed of a sensitive film and interdigitated electrodes. The sensitive film is titanium dioxide prepared by the sol-gel method. The titanium dioxide is coated on the interdigitated electrodes. The humidity sensor requires a post-process to remove the sacrificial layer and to coat the titanium dioxide. The resistance of the sensor changes as the sensitive film absorbs or desorbs vapor. The readout circuit is employed to convert the resistance variation of the sensor into the output voltage. The experimental results show that the integrated humidity sensor has a sensitivity of 4.5 mV/RH% (relative humidity) at room temperature

An acetone microsensor with a ring oscillator circuit fabricated using the commercial 0.18 μm CMOS process

This study investigates the fabrication and characterization of an acetone microsensor with a ring oscillator circuit using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The acetone microsensor contains a sensitive material, interdigitated electrodes and a polysilicon heater. The sensitive material is α-Fe2O3 synthesized by the hydrothermal method. The sensor requires a post-process to remove the sacrificial oxide layer between the interdigitated electrodes and to coat the α-Fe2O3 on the electrodes. When the sensitive material adsorbs acetone vapor, the sensor produces a change in capacitance. The ring oscillator circuit converts the capacitance of the sensor into the oscillation frequency output. The experimental results show that the output frequency of the acetone sensor changes from 128 to 100 MHz as the acetone concentration increases 1 to 70 ppm

Manufacture of Radio Frequency Micromachined Switches with Annealing

The fabrication and characterization of a radio frequency (RF) micromachined switch with annealing were presented. The structure of the RF switch consists of a membrane, coplanar waveguide (CPW) lines, and eight springs. The RF switch is manufactured using the complementary metal oxide semiconductor (CMOS) process. The switch requires a post-process to release the membrane and springs. The post-process uses a wet etching to remove the sacrificial silicon dioxide layer, and to obtain the suspended structures of the switch. In order to improve the residual stress of the switch, an annealing process is applied to the switch, and the membrane obtains an excellent flatness. The finite element method (FEM) software CoventorWare is utilized to simulate the stress and displacement of the RF switch. Experimental results show that the RF switch has an insertion loss of 0.9 dB at 35 GHz and an isolation of 21 dB at 39 GHz. The actuation voltage of the switch is 14 V

Design and Characterization of a High Resolution Microfluidic Heat Flux Sensor with Thermal Modulation

A complementary metal-oxide semiconductor-compatible process was used in the design and fabrication of a suspended membrane microfluidic heat flux sensor with a thermopile for the purpose of measuring the heat flow rate. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, a low pass filter, and a lock-in amplifier can yield a resolution 20 nW with a sensitivity of 461 V/W. The thermal modulation method is used to eliminate low-frequency noise from the sensor output, and various amounts of fluidic heat were applied to the sensor to investigate its suitability for microfluidic applications. For sensor design and analysis of signal output, a method of modeling and simulating electro-thermal behavior in a microfluidic heat flux sensor with an integrated electronic circuit is presented and validated. The electro-thermal domain model was constructed by using system dynamics, particularly the bond graph. The electro-thermal domain system model in which the thermal and the electrical domains are coupled expresses the heat generation of samples and converts thermal input to electrical output. The proposed electro-thermal domain system model is in good agreement with the measured output voltage response in both the transient and the steady state

Hybrid nanomaterial and its applications: IR sensing and energy harvesting

In this dissertation, a hybrid nanomaterial, single-wall carbon nanotubes-copper sulfide nanoparticles (SWNTs-CuS NPs), was synthesized and its properties were analyzed. Due to its unique optical and thermal properties, the hybrid nanomaterial exhibited great potential for infrared (IR) sensing and energy harvesting. The hybrid nanomaterial was synthesized with the non-covalent bond technique to functionalize the surface of the SWNTs and bind the CuS nanoparticles on the surface of the SWNTs. For testing and analyzing the hybrid nanomaterial, SWNTs-CuS nanoparticles were formed as a thin film structure using the vacuum filtration method. Two conductive wires were bound on the ends of the thin film to build a thin film device for measurements and analyses. Measurements found that the hybrid nanomaterial had a significantly increased light absorption (up to 80%) compared to the pure SWNTs. Moreover, the hybrid nanomaterial thin film devices exhibited a clear optical and thermal switching effect, which could be further enhanced up to ten times with asymmetric illumination of light and thermal radiation on the thin film devices instead of symmetric illumination. A simple prototype thermoelectric generator enabled by the hybrid nanomaterials was demonstrated, indicating a new route for achieving thermoelectricity. In addition, CuS nanoparticles have great optical absorption especially in the near-infrared region. Therefore, the hybrid nanomaterial thin films also have the potential for IR sensing applications. The first application to be covered in this dissertation is the IR sensing application. IR thin film sensors based on the SWNTs-CuS nanoparticles hybrid nanomaterials were fabricated. The IR response in the photocurrent of the hybrid thin film sensor was significantly enhanced, increasing the photocurrent by 300% when the IR light illuminates the thin film device asymmetrically. The detection limit could be as low as 48mW mm-2. The dramatically enhanced sensitivity and detection limit were due to the temperature difference between the two junctions formed by the nanohybrid thin film and copper-wire electrodes under asymmetric IR illumination, and the difference between the effective Seebeck coefficient of the nanohybrid thin film and that of the Cu wires. The IR sensor embedded in polydimethylsiloxane (PDMS) layers was also fabricated and tested to demonstrate its potential application as a flexible IR sensor. In another application, energy harvesting, a new type of thermoelectric microgenerator enabled with the SWNTs-CuS nanoparticles hybrid nanomaterial, was fabricated. This type of microgenerator did not require any cooling or heat sink element to maintain the temperature difference or gradient in the device. Instead, the integrated nanomaterials in the device enhanced the local temperature and thus produced and maintained an intrinsic temperature difference or gradient across the microgenerator, thereby converting light and heat directly into electricity. In order to enhance the maximum output voltage, the incoming light had to be focused on the thin film region. A tunable lens was fabricated to collect and focus the ambient light on the thin film to enhance the output voltage of the microgenerators. The tunable lens was fabricated with a flexible polymer, PDMS. Therefore, the focal length of the tunable lens can be adjusted by pumping oil into the lens chamber to deform a PDMS membrane, resulting in the changed focus of the lens. In order to enhance the output power, two different arrays of thermoelectric generators in series and in parallel were fabricated. A hybrid nanomaterial thin film was also used to enhance the temperature gradient of the thermoelectric generators. For the devices in series, the generated voltage of all thermoelectric generators was combined together to enhance the output voltage. With the device in parallel, it can be used to combine all of the current of thermoelectric generators together to enhance the output current

Amélioration du rendement énergétique des amplificateurs de puissance microondes par conversion et recyclage de l'énergie thermique

Cette étude consiste à concevoir un système de récupération et recyclage de l’énergie thermique dissipée d’un amplificateur de puissance microonde pour améliorer son efficacité énergétique. Le système de récupération est composé par un convertisseur thermoélectrique et un adaptateur de puissance : le convertisseur thermoélectrique est un microgénérateur planaire (μTEG) qui permet de convertir le flux reçu de l’amplificateur en une énergie électrique par effet de Seebeck. L’adaptateur des puissances est composé d’un convertisseur DC/DC piloté par un contrôleur MPPT assurant le couplage de l’énergie électrique récupérée avec l’alimentation de l’amplificateur de puissance. Le rendement du microgénérateur proposé est optimisé à l’aide d’un nouveau modèle thermoélectrique pour les structures planaires synthétisé par une analogie thermique-électrique, dont on a montré que ce rendement dépend essentiellement de la figure de mérite des matériaux utilisés et les dimensions de la topologie du microgénérateur. Une validation de cette approche est faite par l’utilisation des trois thermocouples différents. Les simulations analytiques montrent qu’un μTEG basé sur le couple N-P du Tellurure de Bismuth Bi2Te3 permet d’avoir le rendement le plus élevé (3.5%) devant le couple Ag-Ni (0.016%) et le TAGS75 (0.5%), car il a la figure de mérite du son thermocouple la plus élevée (ZT=0.0066), ce qui le rend le plus convenable pour la conversion de l’énergie thermique. Des simulations multiphysiques avec le logiciel COMSOL® ont été effectuées sur un μTEG basé sur le couple (Ag-Ni) pour voir la distribution de chaleur sur sa topologie, ainsi que l’évolution du gradient effectif en fonction du temps. Ces simulations montrent que notre modèle thermoélectrique (analytique) peut estimer le même comportement du rendement que celui obtenu du la simulation numérique. La dernière partie est consacrée pour le couplage de l’énergie électrique récupérée avec l’amplificateur de puissance qui opère à des températures <100°C. Le système complet est implémenté sur SIMULINK®, la simulation montre que le système d’adaptation ramène la puissance récupérée d’un μTEG (basé sur le couple N-P Bi2Te3) à 24.5 mW au lieu de 7.7 mW générée sans ce dispositif, ce qui correspond à l’amélioration du rendement énergétique de l’amplificateur de puissance RF de 0.75%