Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

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Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

Systems, devices and methods are provided for providing sensing and therapy functions using a chronically-implanted device. According to one embodiment, the device includes a structure adapted to be chronically placed within a biosystem, and further includes sensing circuitry and therapy-providing circuitry attached to the structure. The sensing circuitry is adapted to sense mechanical parameters in the biosystem. The therapy-providing circuitry is adapted to provide therapy to the biosystem. According to various embodiments of the device, the sensing circuitry is further adapted to sense electrical and/or chemical parameters in the biosystem, and/or is adapted to provide electrical therapy and/or to provide drug-eluting therapy. One embodiment of the device includes a stent-like structure adapted to be chronically placed intravascularly in the biosystem.

Chronically-implanted device for sensing and therapy

MEMS Mechanical Sensors

Capacitive sensors for the detection of mechanical quantities all rely on a displacement measurement. The movement of a suspended electrode with respect to a fixed electrode establishes a changing capacitor value between the electrodes. This effect can be measured and if the mechanical quantity controls the movable electrode, a sensor is realized. Since the value of the capacitor is directly related to its size, and a small capacitor means high noise susceptibility, capacitive sensors should be as large as possible. Capacitive pressure sensors have been developed with success for industrial applications, where large membrane sizes are not a critical issue. However, most centres of expertise in silicon sensors show an interest in exploiting silicon technology to produce capacitive pressure sensors as well. From the above, this miniaturization trend appears to be an unsound idea. On the other hand, the principle of capacitive sensors allows the realization of measuring systems with so far unknown performance. Indeed, the capacitive sensor reveals distinct advantages when compared to its piezoresistive counterpart: high sensitivity, low power consumption, better temperature performance, less sensitive to drift, etc. Nevertheless, only a minor fraction of the market for pressure sensors is taken up by capacitive-type sensors. When observing the characteristics of capacitive sensors, it may seem surprising to encounter so few devices in real-world applications. The reasons for the lack in breakthrough can be found in the design complexity and the requirements for a matched sensing circuit. This paper will extensively discuss the justification of the choice for this research effort, and will elaborate on the techniques to fabricate the devices based on electronic manufacturing procedures. Basically, silicon capacitive sensors differ from piezosensors in that they measure the displacement of the membrane, and not its stress! This has important implications on the final assembled device: less package-induced problems can thus be expected. However, a far more important issue is their extremely high sensitivity, together with a low power consumption. These issues make them especially attractive in biomedical implant devices, or in other telemetry applications, where power is not randomly available. So far, this is the only field of success for these sensors. However, due to the interesting detection principle, new fields of application emerge, offering unique and superior performance when compared to available sensors. Uniaxial accelerometers are a good example, where extremely high cross-sensitivity reduction can be obtained.

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Capacitive sensors: When and how to use them☆

Capacitive micromachined ultrasonic transducer (MUT) technology is a prime candidate for next generation imaging systems. Medical and underwater imaging and the nondestructive evaluation (NDE) societies have expressed growing interest in cMUTs over the years. Capacitive micromachined ultrasonic transducer technology is expected to make a strong impact on imaging technologies, especially volumetric imaging, and to appear in commercial products in the near future. This paper focuses on fabrication technologies for cMUTs and reviews and compares variations in the production processes. We have developed two main approaches to the fabrication of cMUTs: the sacrificial release process and the recently introduced wafer-bonding method. This paper gives a thorough review of the sacrificial release processes, and it describes the new wafer-bonding method in detail. Process variations are compared qualitatively and quantitatively whenever possible. Through these comparisons, it was concluded that wafer-bonded cMUT technology was superior in terms of process control, yield, and uniformity. Because the number of steps and consequent process time were reduced (from six-mask process to four-mask process), turn-around time was improved significantly.

Capacitive micromachined ultrasonic transducers: fabrication technology

In this paper a single chip pressure and tenperature sensor system with on chip electronics is presented. The capacitive pressure sensor is fabricated using a CMOS process with additional surface micromachining steps to form a membranes. The membrane dimensions have been optimized for a pressure range of 2, 3.5, 10 and 35 bars, respectively. The temperature sensor shows a straight linear output signal in a temperature range of 0 to 70 °C. For the signal processing switched capacitor circuits are used. The sensor signals are converted to a pulse width modulated output signal. The silicon chip has an active area of 3.5 mm 2 . Between 0 and 80 °C a temperature dependence of the pressure segnal of less than 200 ppm/°C referring to full scale was found.

Surface micromachined pressure sensors with integrated CMOS read-out electronics

In medical intensive care, measurement of vital blood parameters is time-consuming and can be inconvenient to the patient A system which processes the signals of the on-chip pressure and temperature sensors is presented This includes signal conditioning and amplification using switch-capacitor techniques Multiplexing some blocks helps to reduce chip area To minimize noise sensitivity, digital transmission using a pulsewidth modulated signal is implemented This also reduces the number of connections to five wires for power and ground, a clock for timing and running the switch-capacitor circuitry, and two lines for digital transmission and control Using a 3- mu m CMOS process optimized for highly reliable analog circuits, the chip size can be limited to 72*07 mm/sup 2/ The chip can be embedded in a catheter 1 mm in diameter, at the same time allowing injection of medicine directly into the arterial blood stream The catheter chip presented is part of a monitoring system that allows the doctor to do online analysis of blood pressure and temperature >

A CMOS sensor and signal conversion chip for monitoring arterial blood pressure and temperature

The fabrication of capacitive pressure sensors using silicon integrated circuit processing is described. The pressure sensors were fabricated using planar etch processing techniques. This results in very small sensors having membrane diameters between 50 μm and 150 μm. The pressure dependence was studied up to 5 bars. Concepts for on chip signal conditioning by using the switch-capacitor method are given.

CMOS Compatible Capacitive Pressure Sensor with Read-Out Electronics

A single-chip pressure and temperature sensor system with on chip electronics for measuring blood pressure and temperature in human arteries is presented. The pressure sensor is fabricated by surface micromachining techniques using a CMOS process. For the signal processing switched capacitor circuits are used. The sensor signals are converted to a pulse width modulated output signal.

http://iopscience.iop.org/article/10.1088/0960-1317/2/3/020/pdf

M. Kandler

Papers

Surface micromachined pressure sensors with integrated CMOS read-out electronics

A CMOS sensor and signal conversion chip for monitoring arterial blood pressure and temperature

CMOS Compatible Capacitive Pressure Sensor with Read-Out Electronics

A miniature single-chip pressure and temperature sensor

Multisensor Catheter For Invasive Measuremt Of Blood Parameters