1 National Kaohsiung First University of Sci. & Tech. Microsensors 2 Department of Mechanical and Automation Engineering National Kaohsiung First Univ

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1 1 National Kaohsiung First University of Sci. & Tech. Microsensors 2 Department of Mechanical and Automation Engineering National Kaohsiung First University of Science and Technology Concurrent Engineering Design Lab. Chemical Sensors 2

3 Sensor Matrix Instead of the global detection in conventional methods, chemical micro system

2 2 Applications of Chemical Sensors Detect the presence or concentration of a chemical substance in a solution. About 60% are gas sensors. local measurement in a real-time environment. 3 Sensor Matrix Instead of the global detection in conventional methods, chemical micro system can analyze the chemical distribution over a domain. Oxygen profile using sensor matrix 32 X 32 in 3cm X 3 cm. 4

Transducer (IDT) Sensor Principle The capacitance of IDT deviates due to the change of the dielectric

3 3 General Structure of a Chemical Sensor Major sensor principles: Potentiometer principle in connection with field effect transistors (FET) Acoustic sensors using the change of mass Optical sensors 5 Interdigital Transducer (IDT) Sensor Principle The capacitance of IDT deviates due to the change of the dielectric properties of the sensitive layer (eg. SnO 2 ). Good for measuring humidity, concentration of sulfur dioxide or ethanol. 6

When a gas is burnt, energies are released, that causes a temperature increase specific to the

4 4 Pellistor Sensor Principle Determine concentration of gases. Measure the increase of temperature due to a chemical reaction. When a gas is burnt, energies are released, that causes a temperature increase specific to the gas on the catalytical surface. High working temperatures of up to 700 C causes problems to silicon. 7 Optical Sensor Principle -1 Interferometer (Photodiodes) 8

$with the waveguide and changes its index of refraction.$ The amount of light striking the photodiode sensor is proportional to the

5 5 Optical Sensor Principle -2 Coupling Grid The substance has direct contact with the waveguide and changes its index of refraction. The amount of light striking the photodiode sensor is proportional to the concentration of the substance. 9 Microspectrometer Source: Fundamentals of Microfabrication - Madou 10

6 Field Effect Transistor Sensor Principle Ion-sensitive FET are used to measure the concentration of ions of various elements such as hydrogen, sodium, potassium or calcium.

6 6 Field Effect Transistor Sensor Principle Ion-sensitive FET are used to measure the concentration of ions of various elements such as hydrogen, sodium, potassium or calcium. 11 The ion-sensitive layer deposited on the gate area of the transistor. V GS changes by the ions in the chemical substance. FET Sensor Principle The change of V GS is detected by adjusting V ref. V T I DS =k(v GS -V T ) 2 12

The mass change affects the resonant frequency of the a standing acoustic wave in a mechanical structure such as a

7 7 Resonance Quartz Sensor Principle The chemical reaction between the substance and the sensitive layer changes the sensor mass. The mass change affects the resonant frequency of the a standing acoustic wave in a mechanical structure such as a membrane,cantilever, or solid. 13 Principle of Standing Waves If two sinusoidal waves of the same amplitude and wavelength travel in opposite directions along a stretched string, their interference with each other produces a standing wave. 14

8 Reflections at a Boundary When the string is tied to a wall (a), the

When the string is tied to a ring (b), the pulse is not inverted by

We can set up a standing wave in a stretched string by allowing a

8 8 Reflections at a Boundary When the string is tied to a wall (a), the reflected pulse is inverted from the incident pulse. When the string is tied to a ring (b), the pulse is not inverted by the reflection. We can set up a standing wave in a stretched string by allowing a traveling wave to be reflected from the far end of the string. 15 Standing Waves and Resonance Standing waves pattern on a string and on a membrane. 16

9 9 Waveguide Sensor Principle The sensitive layer interacts with the analyzed substance and the wave transmission changes due to damping. 17 Acoustic Waves Transducers Principle of Acoustic Wave Interdigital Transducer (IDT) over a piezoelectric layer. Using IDT as actuator and sensor. Sensitive layer, interacting with the chemical substance, changes the phase or the resonance frequency of SAW. W IDT Actuator λ IDT Sensor λ 18

10 10 Raleigh Waves Raleigh waves (Surface Acoustic Wave, SAW) 19 Lamb Waves Lamb waves (Flexural Plate Wave, FPW) Direction of Propagation (a) Axle of Center T= 0 (Static State) Wavelength Particle Motion (b) Axle of Center 20

Array of 400 µm long silicon cantilevers made of (0.4 µm Pt catalytic layer) / (0.4 µm Al) / (1.5 µm silicon).

11 11 Ion Sensitive FET Sensor Continuous measurement of the gases in blood (like po 2 or pco 2 ) and of the ph value are very important in surgery. Use ion-sensitive field effect transistors /ph 21 A chemical reaction is transformed into mechanical motions by using the bimetal effect. Array of 400 µm long silicon cantilevers made of (0.4 µm Pt catalytic layer) / (0.4 µm Al) / (1.5 µm silicon). The reaction heat causes the bimetal cantilevers to bend. Bimetal Sensor Displacement measured by a scanning force microscope with an optical laser detector. Sensor resolution: 0.01 nm, (ie C) 22

12 Sensors Based on a Zigzag IDT Capacitance The concentrations Of CO 2 in a fluid is measured with AMO/PTMS whose dielectric properties is changed with the CO

23 Sensors Based on IDT Capacitance Another interdigital transducer sensor for detecting CO, C0 2, N0 2 and water concentrations.

12 12 Sensors Based on a Zigzag IDT Capacitance The concentrations Of CO 2 in a fluid is measured with AMO/PTMS whose dielectric properties is changed with the CO 2. Zigzag design has better capacitive properties. NiCrAu capacitor, Zigzag width varies between 2.5~15 µm. AMO/PTMS thickness varies between 0.9~1.2 µm. 23 Sensors Based on IDT Capacitance Another interdigital transducer sensor for detecting CO, C0 2, N0 2 and water concentrations. The sensitivity and selectivity of SnO 2 can easily be enhanced by a catalyst. (50nm n-doped) (a few nm, sputtered) (Activate the metal oxide gas reaction) (1µm, used as an electrical insulator) 24

13 13 BioSensors 25 Sensing Principles Similar principles as chemical sensors. The biologically sensitive elements such as enzymes, receptors and antibodies are integrated with the sensor. In many molecular interactions, gases are either released or consumed, that can be detected by a chemical sensor. Major difficulties Produce only short-lived sensors because the proteins are not very stable for a very long time. Immobilization of the proteins. Biosensors are divided into metabolism sensors and immuno-sensors. 26

14 14 Metabolism Sensors Biosensitive enzymes as biocatalysts to detect molecules in a substance and to catalyze a chemical reaction. The analyzed substance is chemically transformed and the course of a reaction can be detected by a chemical sensor. (Enzyme) For instance, Phosphate concentration can be determined from the amount of oxygen consumed. 27 Immuno-sensors To detect chemically inactive molecules in a substance. Immobilized antibody molecules ("lock") on the sensor surface bond with an antigen molecule "key" in the substance. 28

15 Immuno-Sensor with IDT Ti/Pt 70 900 µm 1 3.

15 15 Immuno-Sensor with IDT Ti/Pt µm µm nm 29 Immuno-sensor with IDT IDT Redox IDT 30 30

31 Single Channel Metabolism Sensors The thermistors T 0 and T 1, are responsible for measuring the enzyme located in the reaction range E 1.

16 16 Single Channel Metabolism Sensors Several thermal metabolism sensors can be installed in one sensor system. Thermistors are made by doping and etching the quartz chip. T x -thermistor, E x - enzyme reaction range. 31 Single Channel Metabolism Sensors The thermistors T 0 and T 1, are responsible for measuring the enzyme located in the reaction range E 1. The reaction between the enzymes E i with the substances marked as S i generates heat that is registered by the thermister. : Temperature difference across E 1 : Temperature difference across E 2 S i : substances to be measured EX: urea and penicillin-v 32

17 17 Temperature Sensors 33 Fiber- Optical Thermometer The multi-modal glass fiber is made of materials that have different temperature coefficients in the core and the mantle. Temperature variation in the sensor surrounding changes the local index of refraction in the fiber, that results in an optical light attenuation. Measure temperatures of up to 90 C with in accuracy of 0.1 C. 34

18 18 Liquid Crystal Thermometer The thermotropic liquid crystals can be used for measuring temperature since their optical properties are determined by the molecular alignment, which is temperaturedependent. Photodiode 35 36

20 Flow Sensors 39 Two-mode Flow Sensor Two modes: Elapsed time of the locally heated flow medium: A 5 Hz signal was applied to the heater and the time was measured until the temperature rise is

20 20 Flow Sensors 39 Two-mode Flow Sensor Two modes: Elapsed time of the locally heated flow medium: A 5 Hz signal was applied to the heater and the time was measured until the temperature rise is recorded by the 2 nd sensor. Thermal dilution: the heater supplies constant energy, and measure the temperature difference between the upstream and downstream sensors. Sensitivity: 0.05~0.2 ml/min. 40

disc, an implanted heating resistor, a ring-like silicon dioxide layer

21 21 Force-Measuring Flow Sensor 3mm 1mm 30µm 5~500 ml/min 4.3 µv/v per µl/min 41 Thermal Flow Sensor Consist of a circular silicon disc, an implanted heating resistor, a ring-like silicon dioxide layer (thermal insulation) around the disc, and a 3 µm thick polyimide film as chip cover. CMOS CMOS 42

投影片 1

投影片 1 Coherence ( ) Temporal Coherence Michelson Interferometer Spatial Coherence Young s Interference Spatiotemporal Coherence 參料 [1] Eugene Hecht, Optics, Addison Wesley Co., New York 2001 [2] W. Lauterborn,