High-resolution pressure sensor
Efficient signal processing IC for MEMS pressure sensors
The read out ASIC ICAPS has been developed for miniaturized capacitive MEMS sensors that are wired in a fully differential bridge circuit. The read out ASIC ICAPS consists in the core piece of a 18 bit Sigma Delta ADC that has the ability to read out different sensors, like the integrated temperature and VDD sensor, due to its circuitry. The internal temperature sensor has a target resolution of 0.05 K. The structure of the Sigma Delta modulator has been optimized with regard to noise, immunity to interference and low power consumption for the use in energy self-sufficient applications, like battery-powered applications or in RFID sensors. This way, a resolution of the pressure sensor of 0.065 mBar can be achieved. In complete measurement cycles with an output of the measured temperature, pressure and supply voltage values a sample rate of up to 200 Hz can be reached. To achieve higher data rates, every sensor can be individually converted and read out. For an optimum use of the sample rate the ICAPS ASIC can be operated in a continuous measurement mode. In this mode the SPI interface is converted via a MISO pin into a ready signal. Due to the adjustability of the oversampling rate of the Sigma Delta modulator, a specific ADC resolution can be set for every individual sensor. With the implementation of an arithmic unit or an RISC-V microprocessor including a non-volatile memory, in which calibration and configuration data can be stored, both print data values and raw data can be put out. Because the ICAPS ASIC is operated in an energy-efficient way and has a standard SPI interface, it can be applied in transponder and wired systems. Application fields can be medicine, automotive and industrial applications that support a supply voltage and SPI interface level of 3.3 V.
CMOS postprocessing for surface-optimized sensor solutions
To get a surface-optimized ASIC the development took place in a 0.18 μm process. At Fraunhofer IMS the capacitive MEMS sensors are mounted subsequently to the ASIC production. Because the sensors are brought out over the circuit, space can be saved through the 3D integration in the sense of miniaturization. The achieved chip surface has a size of 6 mm². Currently, capacitive pressure sensor elements are mounted onto the read-out ASIC ICAPS. The pressure sensors are designed for a specific pressure range of up to 1300 mBar. Through the adaption of the pressure box diameter and the number of pressure sensor elements other pressure ranges can be realized.
The project is funded by the Federal Ministry of Education and Research (BMBF) under the project number 13GW0275B.