Tsunehisa Tanaka

Front-end processor using BBD distributed delay-sum architecture for micromachined ultrasonic sensor array

Micromachined technology makes it possible to integrate the ultrasonic sensor with the front-end processing circuit together, and make an ultrasonic system smart, compact and low cost. An ultrasonic sensor array with resonant frequency of about 60 kHz is fabricated for airborne applications, using sol-gel derived Pb(Zr,Ti)O/sub 3/ thin film and Si-based micromachining technique. The distributed delay-sum architecture based on a bucket brigade device (BBD) is employed for the beamforming of the sensor array in order to reduce chip area, simplify system design, improve power efficient and achieve monolithic integration. A charge attenuator is proposed to increase the dynamic range of the input signal and overcome the charge overflowing in bucket capacitors. A charge amplifier based preamplifier is used to interface the sensor array and beamformer. A prototype front-end processor shows good SNR with the dynamic range larger than 50 dB, and a beamforming performance consistent to the theoretical calculation very well.

Preferred orientation and ferroelectric properties of lead zirconate titanate thin films

Abstract Highly (111) oriented perovskite PZT thin films have been prepared by annealing FTS-deposited samples. The effects of the substrate temperature, sputtering power, annealing temperature and heating rate for annealing on the crystalline orientation were investigated. The sample prepared under the optimum condition showed excellent ferroelectric properties with P r of 45 μC/cm 2 and P s of 79 μC/cm 2 .

Structural and electrical properties of highly oriented Pb(Zr,Ti)O3 thin films deposited by facing target sputtering

Abstract The Pb(Zr,Ti)O 3 thin films with single (111) oriented perovskite phase and excellent electrical properties have been prepared by annealing the as-deposited samples. The orientation of crystals depends strongly on both the deposition temperature and annealing temperature. The sample annealed at 606°C has the best (111) orientation. When the sample is annealed at lower temperature, the relative content of (111) oriented perovskite phase decreases quickly with increase of deposition temperature. The deposition temperature has little effects on the orientation when the sample is annealed at higher temperature. The effects of deposition temperature and annealing temperature on the crystallographic structures and electrical properties of PZT thin films were investigated in this paper. The sample deposited at 285°C and annealed at 606°C has the maximum value of polarization, which displays excellent ferroelectric properties. The typical P r and P s values are 57 and 101 μC/cm 2 , respectively.

Development of Capacitive Ultrasonic Sensor with Parylene Diaphragm Using Micromachining Technique

In this paper, we reports the development of a miniaturized capacitive ultrasonic sensor with a Parylene diaphragm using a micromachining technique. Since the polymer diaphragm is flexible and nonbrittle, good sensitivity and durability are expected. Moreover, Parylene has good complementary metal oxide semiconductor (CMOS) compatibility, since it can be deposited at room temperature. Practical sensor devices were fabricated, and their performance was characterized. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge with an open-circuit sensitivity of 0.3 mV/Pa. A well-damped waveform was obtained by setting appropriate acoustic holes. The ranging system using this sensor can detect distances up to 1 m with an error of less than 1 mm. The developed sensor can receive ultrasound from a wide area. The wide directivity could be effective for realizing the omni-directional characteristics of the future arrayed sensor, which contains many of the developed sensors.

Integrated analog beam former based on bucket brigade device for micromachined ultrasonic sensor array

Micromachined ultrasonic sensors are promising in the applications including medical imaging, non-destructive evaluation (NDE), ranging, and object detections. Bucket brigade device (BBD) was used as the analog beam former for piezoelectric micromachined ultrasonic sensor phased array. The works on the optimization of BBD, including improvement of the transfer efficiency and dynamic range, and simplification of system design were discussed in details. The parasitic insensitive approach was proposed to optimize the properties of BBD delay line, and measured results indicated that this approach achieved larger charge transfer efficiency, larger dynamic range, and higher frequency than the conventional BBD. Furthermore, the BBD distributed delay-sum architecture was proposed to reduce chip area, simplify system design, and achieve monolithic integration. The measured results indicated that BBD distributed delay-sum architecture showed the beam forming property that is consistent to the theoretical calculation very well.

Characterization of lead zirconate titanate thin films deposited at low temperature by reactive facing target sputtering

Lead zirconate titanate thin films have been deposited on platinized silicon substrate at low temperature by reactive facing target sputtering. The effects of substrate temperature, total gas pressure, sputtering ambience, input power and target composition on the phase composition of PZT thin film were investigated. By controlling the sputtering conditions, highly (111) oriented perovskite PZT thin films can be obtained, and the samples show ferroelectric properties.

Sensitivity of ultrasonic sensor structures having multilayer diaphragm structure

Arrayed ultrasonic sensors utilizing a piezoelectric thin film (lead-zirconate-titanate film: Pb(Zr0.52Ti0.48)O3) are fabricated with multilayered diaphragm structures. The different thermal and elastic characteristics of each layer lead to residual stress during high-temperature deposition processes; consequently the resultant composite membrane is bowed. Here, we present the influence of the initial membrane deflection, which originates from residual stress, on the sensitivity of the sensor chips. Three types of sensor structure having different film thicknesses and constitutions are fabricated, which correspond to different sensitivities (82–98 µV/Pa). The sensitivity is mainly influenced by the initial membrane deflection. These results are discussed in relation to the stress generation in each composite membrane structure and PZT film properties.

(111) Preferred Oriented Pb(Zr,Ti)O3 Thick Films Prepared by Multilayer Process and Its Application to Ultrasonic Sensors

We report the deposition of Pb(Zr0.52Ti0.48)O3 (PZT) thick films on Pt/Ti/SiO2/Si substrates using a multilayer process to suppress the problem of crack formation due to thermal stress. The thickness dependences of film structure, ferroelectric and dielectric properties were investigated over the thickness range of 0.24–4.6 µm. A strong (111) orientation was obtained from all films deposited in the experiments. For a constant applied field of 170 kV/cm, remanent polarization, 2Pr developed from 14 µC/cm2 to 60 µC/cm2, as film thickness increased from 0.24 to 4.6 µm. Dielectric constant also increased with film thickness, and reached the maximum value of 1300 at the thickness of 4.6 µm. These trends were interpreted in terms of the interfacial effect on the electrical characteristics. A thin-film-type ultrasonic sensor was fabricated by depositing a multilayered PZT thick film onto an SOI substrate having a membrane structure, and its characteristics are reported.

Development of a Capacitive Ultrasonic Sensor Having Parylene Diaphragm

The present paper reports the development of a capacitive ultrasonic sensor having Parylene diaphragm. Parylene diaphragm is flexible and non-brittle, allowing good sensitivity and durability. The resonant frequency under the tensile stress of Parylene and the influence of the number and the radius of acoustic holes on damping ratio are investigated by FEM simulation. Practical sensor devices are fabricated. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge. The ranging system using this sensor can detect the distance up to 1 m with the error less than 1 mm. The developed sensor can be approximated to be non-directional.

Residual Stress and Membrane Deflection Influences on the Ultrasonic Sensor Device

The influences of residual stress on the piezoelectric ultrasonic sensors having composite membrane structure included PZT (Pb(Zr0.52Ti0.48)O3) thin film are presented. Due to the different thermal and elastic characteristics of each constitutive layer, a subsequent residual stress and deflection is usually generated on the composite membrane. We discuss the influences of residual stress on the Si-based integrated sensor device in the two point of view; the mechanical behaviors and piezoelectric thin film properties. The composite layer structure and fabrication process especially related to thermal process have significant effects on the stress state of the composite membrane. The relationships among the stress states, deflections of composite membrane and sensitivities of sensor devices are considered.