Refine
Document Type
- Article (8)
Language
- English (8)
Has Fulltext
- yes (8)
Is part of the Bibliography
- yes (8)
Keywords
- MEMS (6)
- Mikrofon (4)
- Drucksensor (2)
- Dünne Schicht (1)
- Elektrotechnik (1)
- Flip-Chip-Technologie (1)
- Kalibrieren <Messtechnik> (1)
- Mikroelektronik (1)
- Mobilfunk (1)
- Smartphone (1)
Institute
This paper describes a novel method for trimming a low noise, differential micro-electromechanical system (MEMS) microphone with a state of the art signal to noise ratio (SNR) of 66 dB(A) and a sensitivity of -38 dBV/Pa @ 1 kHz after completing the fabrication process. The method allows compensating the electroacoustic variations caused by process tolerances and reducing specification limits of the microphone sensitivity from ±3 dB to ±0.5 dB. Trimming is done by programming the bias supply voltage of the capacitive membrane-backplate-system and the gain factor of the output pre-amplifier. Microphone sensitivity can be modified within a range of 11.2 dB. Thus the standard deviation of the sensitivity of a production batch could be reduced from 0.97 dB to 0.11 dB. Furthermore the SNR could be increased to 66.5 dB(A).
Barometric MEMS pressure sensors must be calibrated at several temperatures and pressures. The fewer calibration points are needed to fulfill a sensor specification, the faster sensor production is. This paper proposes a polynomial approach for determining optimal sensor calibration, using the minimum number of calibration points necessary. In an experiment the framework is applied to the following sensor types: Bosch BMP085, Bosch BMP180, and EPCOS T5400. Influences of temperature operation range and pressure range are discussed in the experiment. Further, optimal calibration point suggestions are identified.
MEMS microphones must be further miniaturized for use in mobile devices. So we developed packaging technologies for MEMS microphones using flip chip technology instead of wire bonding. The first two generations have the sound hole in a ceramic interposer at the bottom side of the package. Now a new flip chip microphone package with the sound hole on the top side has been developed. The new package technology combines a large acoustic reference volume for good signal to noise ratio with small size. Compared to other microphone packages the sensitivity is improved by 3 dB. The front volume is small to avoid resonances in the acoustic frequency range.
Fabrication and characterization of a piezoresistive humidity sensor with a stress-free package
(2014)
A highly miniturized piezoresistive humidity sensor has been developed. The starting point of the developement was a 1x1 mm2 piezsoresistive pressure sensor chip. As sensing material, a polyimide was used that swells with increasing adsorption of water molecules. To convert the swelling into an electrical signal, a thin layer of the polimide was deposited onto the bending plate of the pressure sensor. The humidity sensor was characterized in a climate chamber. The measurements show a sensittivity of 0.25 mV per percent relative humidity (%RH) and a non-linearity of 3.1 % full scale (FS) in the range of 30-80%RH. A high cross-sensitivity to temperature of around 0.5 mV°C was measured, so temperature compensation is necessary. For stress-free packaging of the sensor chip, a novel packaging technology was developed.
Capacitive MEMS microphones are now widely used for mobile phones and headsets. The frequency response of MEMS microphones is influenced by the package geometry. This can be applied to tune the performance of the microphone in the system. Packages with small sound inlet holes are acoustic low-pass filters. The cut-off frequency is determined by the diameter of the holes. In previous work we did not find sufficient agreement between a lumped element simulation and the measured frequency response of the microphones. Now we measured the acoustic resistance of small sound inlet holes directly. The measured resistances agree well with calculated values. The frequency response of MEMS microphones was measured for different sound hole diameters and lengths. The results are in good agreement with calculated transfer functions of the package.
In this paper we present a systematic method to determine sets of close to optimal sensor calibration points for a polynomial approximation.
For each set of calibration points a polynomial is used to fit the nonlinear sensor response to the calibration reference. The polynomial parameters are calculated using ordinary least square fit. To determine the quality of each calibration, reference sensor data is measured at discrete test conditions. As an error indicator for the quality of a calibration the root mean square deviation between the calibration polynomial and the reference measurement is calculated. The calibration polynomials and the error indicators are calculated for all possible calibration point sets. To find close to optimal calibration point sets, the worst 99% of the calibration options are dismissed. This results in a multi-dimensional probability distribution of the probably best calibration point sets.
In an experiment, barometric MEMS (micro-electromechanical systems) pressure sensors are calibrated using the proposed calibration method at several temperatures and pressures. The framework is applied to a batch of six of each of the following sensor types: Bosch BMP085, Bosch BMP180, and EPCOS T5400. Results indicate which set of calibration points should be chosen to achieve good calibration results.
In this paper a new method for sensitivity recalibration of capacitive MEMS microphones is presented. Recalibration can be applied to compensate ageing or environmental influences. Recalibration can be done by measuring the sensitivity for only one bias voltage after a stress test. A microphone with a variable bias voltage can measure its pull-in voltage. Unfortunately, the drift of the pull-in voltage does not correlate with the sensitivity drift. So a true self-calibration without a defined acoustical test signal was impossible.
Microacoustic radio frequency filters are essential electronic components for all devices using wireless communication. For miniaturization and cost reduction it is necessary to further reduce the area for the electrical contacts on the chip. CPB (copper pillar bump) interconnections on radio frequency filters can release valuable chip design area of up to 26 % compared to standard SB (solder bump) interconnections on a Qualcomm TFAP (Thin Film Acoustic Package). We developed a process to deposit CPB interconnections on microacoustic radio frequency filters. A 1.20 mm × 1.60 mm SAW (surface acoustic wave) LTE (Long Term Evolution) band 26 duplexer with a height of 0.20 mm including the CPB interconnections was investigated. Unbiased highly accelerated stress test, damp heat steady state, dry heat, and temperature cycling reliability tests have shown that the new interconnection technology fulfills the reliability requirements of the smart device industry. Two failure modes caused by extended temperature cycling were identified via scanning acoustic microscopy and scanning electron microscopy analyses on cross sections.