Integrated pressure sensor

SiN mask for KOH etching FIGURE 14.1 Schematic of integrated pressure sensor in bulk micromachining. 

Figure 2.8 Typical semiconductor strain gage units (a) unbonded, uniformly doped (b) diffused p-type gage (c) integrated pressure sensor (d) integrated cantilever beam force sensor. (From R S C Cobbold Transducers for Medical Measurements Application and Design, copyright 1974, John Wiley and Sons, Inc.)...

Temperature is a very important parameter in microprocess technology, especially for reactions and processes which need precise temperature control, such as very exothermic reactions. For this, temperature sensors are available as stand-alone modules (Figure 8.7), integrated sensors inside the modules or as peripherals, for example an integrated pressure-sensor unit or the glass-fiber thermometer based on spectroscopy technology. 

In future sensor assemblies should already be constructed by an additional integrated optical sensor, so that the method works without contact. The probe has always a slight distance from the object in this case. Currently it is guaranteed through an integrated pressure sensor that acts in this case as a touch sensor, that the sensor rests on the surface. 

Piezoresistive Sensors. The distinction between strain-gauge sensors and pie2oresistive (integrated-circuit) sensors is minor. Both function by measuring the strain on an elastic element as it is subjected to pressure. A pie2oresistive transducer is a variation of the strain gauge that uses bonded... 

Cavity size (volume) Approx. 50 L Delivered power 1500 W Max. output power 1200 W Temperature control Outside IR remote sensor Immersed fiber-optic probe (optional) Pressure measurement Pneumatic pressure sensor (optional) Cooling system Air flow through cavity 100 m3 h1 External PC Optional not required as integrated key panel is standard equipment ... 

However, very economical measurement of acceleration is possible when the washing machine is equipped with a high-resolution analog pressure sensor with microprocessor control. These pressure sensors come as a separate part or are integrated directly on to the PCB of the washing machine control. They work as differential pressure sensors and measure the static pressure via a hose in the lower part of the suds container, thus measuring the water level in the suds container (Fig. 5.57). 

In addition to absolute pressure measurements, pressure sensors can be used to determine flow rates when combined with a well-defined pressure drop over a microfluidic channel. Integration of optical waveguide structures provides opportunities for monitoring of segmented gas-liquid or liquid-liquid flows in multichannel microreactors for multiphase reactions, including channels inside the device not accessible by conventional microscopy imaging (Fig. 2c) (de Mas et al. 2005). Temperature sensors are readily incorporated in the form of thin film resistors or simply by attaching thin thermocouples (Losey et al. 2001). 

Knowledge of the sample pressure is essential in all high-pressure experiments. It is vital for determinations of equations of state, for comparisons with other experimental studies and for comparisons with theoretical calculations. Unfortunately, one cannot determine the sample pressure directly from the applied force on the anvils and their cross-sectional area, as losses due to friction and elastic deformation cannot be accurately accounted for. While an absolute pressure scale can be obtained from the volume and compressibility, by integration of the bulk modulus [109], the most commonly-employed methods to determine pressures in crystallographic experiments are to use a luminescent pressure sensor, or the known equation of state of a calibrant placed into the sample chamber with the sample. W.B. Holzapfel has recently reviewed both fluorescence and calibrant data with the aim of realising a practical pressure scale to 300 GPa [138]. 

Pressure sensors that give temperature-corrected, linear, analog voltage output are available from Motorola and other manufacturers. In such sensors, the on-chip electronics correct any temperature effects and nonlinearities in the output of the piezoresistors. The on-chip electronics replace a shoebox-size collection of printed circuit boards. The price of this kind of smart sensor is considerably less than 100. The integration of a large amount of circuitry on the chip allows functions like amplification, offset correction, self-testing, autocalibration, interference reduction, and compensation of cross-sensitivities (6). 

The state variables that provide valve position control are used to diagnose the health of the final control element. In addition, some digital valve controller designs integrate additional sensors into their construction to provide increased diagnostic capability. For example, pressure sensors are provided to detect supply pressure, actuator pressure (upper and lower cylinder pressures in the case of a springless piston actuator), and internal pilot pressure. Also, the position of the pneumatic relay valve is available in some designs to provide quiescent flow data used for leak detection in the actuator. 

The micro fluidic devices are integrated into cubic modules of identical shape and size, and can be easily replaced [108], The modules are equipped with individual temperature control, integrated pressure and/or temperature sensors and, upon demand, additional actors such as non-return valves. This modular concept ensures a flexible interconnection of the micro fluidic devices. 

R 18] [A 1] Each module is equipped with a heater (H3-H8) and a fluidic cooling (C03-C06). Temperature sensors integrated in the modules deliver the sensor signals for the heater control. Fluidic data such as flow and pressure are measured integrally outside the micro structured devices by laboratory-made flow sensors manufactured by silicon machining. The micro structured pressure sensor can tolerate up to 10 bar at 200 °C with a small dead volume of only 0.5 pi. The micro structured mass flow sensor relies on the Coriolis principle and is positioned behind the pumps in Figure 4.59 (FIC). For more detailed information about the product quality it was recommended to use optical flow cells inline with the chemical process combined with an NIR analytic or a Raman spectrometer. 

Miniaturized and integrated sensor systems were developed early for pressure and accelerometer sensors. The technology of silicon micromachining leads to sensitive pressure sensors which were marketed early [4]. Also accelerometers were developed mainly driven by the huge market of air bag application and crash sensors [5]. 

In this scheme we have overcome the above problem by introducing organic transistor integrated circuits as a flexible active matrix to read out pressure images, or distribution of pressure. As a result, we have successfully developed large-area, flexible pressure sensors with the number of pressure sensors exceeding 1,000. As shown in Fig. 16.2, the device is manufactured by laminating four different functional films ... 

Fig. 16.2. Integration of organic transistors with pressure-sensitive rubber sheets, (a) A cross-sectional view of the device structure and (b) a circuit diagram of one sensor cell. The device is formed by laminating four different functional films. The pressure sensors are...

We have built a prototype of an interferometric pressure transducer that was designed to be attached to a non-commercial room temperature sorption instrument [3] equipped with a differential membrane sensor (MKS, Baratron 220CD, full range 10 mbar, pressure resolution 0,15 % of full range value). An additional absolute pressure sensor (MKS, Baratron 220 CA) integrated into the set-up provides the average pressure in the manifold and... 

The aim is to eliminate entrance effects as much as possible and any influence on the flow of the pressure tap holes into the channels. This was achieved by integrating on the same silicon chip the microchannel, the pressure taps and the pressure sensors. The fabrication process and the operating mode are described in [28]. The pressure sensors are constituted cf a membrane which is deformed under the fluid pressure and on which is deposited a thin film strain gauge. This strain gauge forms a Wheatstone bridge whose the membrane deformation modifies the electrical resistances. 

---