SeungHwan Yi

Performance of Packaged Piezoelectric Microspeakers Depending on the Material Properties

This paper presents the improved piezoelectric microspeakers that implement a packaging structure with AlN film and are made of composite diaphragms of different residual stresses. The output Sound Pressure Level (SPL) is enhanced more than 10 dB with a higher compressively stressed composite diaphragm (having -20 MPa silicon nitride film as a supporting layer) from 100 Hz to 3 kHz. The best microspeaker produces more than 100 dB SPL into open field around 3 kHz (when measured 10 mm away from the speaker that is driven with 20 Vpeak-to-peak sinusoidal signal). A microspeaker with a square electrode pattern produces more uniform frequency response above 4 kHz than that with a circular electrode pattern.

Dependence of material properties on piezoelectric microspeakers with AlN thin film

This paper reports the dependence of residual stress on the piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film deposited onto Mo/Ti electrode. This successful achievement is followed by using a compressively stressed silicon nitride film as a supporting diaphragm and high quality AlN thin film with compressive residual stress (less than -100 MPa). The sound pressure level (SPL) is relatively small when we use a tensile stressed silicon nitride film, the SPL of the fabricated microspeakers that have compressively stressed composite diaphragm shows more than 60 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with 20 Vpeak-to-peak sinusoidal input biases and 10 mm distances from the fabricated microspeakers to the reference microphone. The packaging structure enhances the low frequency characteristics significantly.

MICROMACHINED PIEZOELECTRIC MICROSPEAKERS FABRICATED WITH HIGH QUALITY ALN THIN FILM

ABSTRACT This paper describes the micromachined piezoelectric microspeakers that can produce the audible signal with 20 V peak-to-peak input voltages. The diaphragm size is 4 × 4 mm2 and the thickness of diaphragm is around 1 micron meter except partially etched piezoelectric area. The maximum sound output pressure of the microspeaker is even higher than ever before with a small diaphragm in high frequency range around 10 kHz. This successful result bases upon using high quality AlN thin film. The deposited AlN thin film shows c-axis oriented columnar structure and very fine grains. The highest SPL (Sound Pressure Level) measured from 300 Hz to 12 kHz shows about 100 dB around 10 kHz in case of circular type microspeaker and about 76 dB in case of cross type, respectively.

The effects of residual stresses in the composite diaphragm on the performance of piezoelectric microspeakers

Piezoelectric microspeakers are fabricated with AlN film on circular and square Mo/Ti electrodes, and the acoustic pressures are measured with and without packaging structure as a function of frequency. As residual stresses of the composite diaphragm are decreased from +20 MPa to −20 MPa, the output pressure of the fabricated chip (square electrodes) is increased from 1.16 mPa to 96.2 mPa. The packaged microspeaker shows enhanced uniform sound pressure level (SPL) from 1 kHz to 15 kHz with more than 100 dB SPL at 2.50 kHz, with square electrodes in particular. For the circular electrodes, the resonant frequency is revealed to be 3.06 kHz, and the SPL at resonant frequency is measured at 107 dB, which is somewhat higher than for the square electrode. However, the output pressures of the microspeaker show lower values than that of the square electrodes at 1 kHz sinusoidal frequency.

CHARACTERISTICS OF PIEZOELECTRIC MICRO-SPEAKER FABRICATED WITH ZNO THIN FILM

ABSTRACT A piezoelectric microspeaker was fabricated on the 5 × 5 mm2 diaphragm with highly c-axis oriented ZnO thin film on a heavily compressive-stressed silicon-nitride film. Four masks were used in the fabrication processes of the piezoelectric microspeaker. 0.5 μ m-thick piezoelectric ZnO film was deposited by RF-magnetron sputtering method on an Al bottom electrode. Then, 0.2 μ m-thick Al film was deposited for the top electrode. To enhance the ZnO film quality for improving the microspeaker performance, two-step deposition technique was adopted. The back-side silicon nitride was patterned, and silicon substrate was removed to make a diaphragm. The speaker output pressure level (SPL) of the fabricated microspeaker was measured with the variation of sinusoidal input frequency and compared to that of the commercial piezo-ceramic speaker. The largest SPL of the microspeaker was about 92 dB at the input voltage of 6Vpeak-to − peak, which was measured at the distance of 3 mm from the microspeaker in open field. The SPL of microspeaker was nearly same as that of a commercial piezo-ceramic speaker.

Temperature Compensation of Novel NDIR CO2 Gas Sensor

We have designed novel optical cavity and simulated it for NDIR gas sensor application. Novel optical cavity enhanced the light focusing effects. In this research, we developed the temperature compensated NDIR CO2 gas sensor for heat exchange system. The output characteristics of developed sensor module shows an exponentially decreasing property and all parameters are temperature dependent. The temperature compensated module has about plusmn 70 ppm error within 40degC temperature span.

Characteristics and Temperature Compensation of Non-Dispersive Infrared (NDIR) Alcohol Gas Sensors According to Incident Light Intensity

This paper discusses the output characteristics of the sensor response of infrared ethanol gas detectors based on incident radiation intensity. Sensors placed at each focal point of two elliptical waveguides were fabricated to yield two module combinations and to verify the output characteristics. A thin Parylene-C film was deposited onto the reflector surfaces of one module. The thermal properties were compared between the sensor (2.0 Ø) and sensor with a hollow disk (1.6 Ø), the disk being mounted at the end of one detector. The fabricated sensor modules were placed inside a gas chamber. The temperature was increased from 253 K to 333 K, over the concentration range from 0 to 500 ppm. As the temperature increases by 10 K, the output of sensor (2.0 Ø) without and with Parylene-C coating typically increased by 70 mV and 52 mV, respectively. However, the sensor output with the hollow disk showed an average decrement of 0.8 mV/50 ppm and 1 mV/50 ppm for module without and with Parylene-C deposition, respectively. For concentrations higher than 50 ppm, the estimation error was around ±5%. Further, the sensitivity to temperature variation and the absorbance of infrared (IR) reflection was found higher for Parylene-C coated module.

Characteristics of Piezoelectric Microspeakers according to the Material Properties

This paper reports the characteristics of piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film according to the materials properties. When we use a tensile-stressed silicon nitride diaphragm as a supporting layer, the Sound Pressure Level (SPL) is relatively small and constant at low frequency region and shows about 70 dB at 10 kHz. However, in case of a compressively stressed composite diaphragm, the SPL of the fabricated microspeakers shows higher output pressure than those of a tensile-stressed diaphragm. It produces more than 66 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with , sinusoidal input biases and at 10 mm distances from the fabricated microspeakers to the reference microphone. From the experimental results, it is superior to have a compressively composite diaphragm in order to produce a high SPL in piezoelectric microspeaker.

NDIR CO 2 Gas Sensor for Improving Indoor Air Quality

We have simulated and proposed novel optical cavity, which has two elliptical mirrors, for NDIR gas sensor module and have tested it from 0 ppm to 2,000 ppm concentration. The proposed sensor module shows the maximum peak voltage at 500 ms pulse modulation time, however, it shows a maximum voltage changes at 200 ms pulse duration with 18,000 times amplification gain. From 0 ppm to 2,000 ppm, the voltage difference of sensor module shows 360 mV at 200 ms pulse duration and 3 sec turn-off time. The response time of designed sensor module is about 30 seconds.