This paper presents a fully integrated ultrasound system based on a single piezoelectric micromachined ultrasonic transducer (PMUT) monolithically fabricated with a 0.13 μm complementary metal oxide semiconductor (CMOS) process analog front-end circuitry. The PMUT consists of an aluminum nitride, AlN, squared device with 80 μm side that resonates at 2.4 MHz in liquid environment. The monolithic integration of the PMUT with the CMOS circuitry allows a reduction of the parasitic capacitance, a reduction of the electronic noise contribution and a clear improvement in the Signal-to Noise ratio (SNR ∼ 27 dB better) compared to a non-integrated equivalent system. A pulse-echo experiment with the single PMUT-on-CMOS for transmitting and sensing simultaneously is demonstrated, ensuring a 17.3 dB SNR, higher than the minimal necessary for accurate fingerprint images, paving the way towards a pixel sized imaging system with no need of multiple simultaneous PMUTs transmitters. Consuming only 0.3 mW and getting an input-referred noise of 3.26 mPa/√Hz at 2.4 MHz, the proposed pulse-echo system achieves a competitive noise efficient factor in comparison with the state-of-the-art.

This paper presents an analog front-end transceiver for an ultrasound imaging system based on a high-voltage (HV) transmitter, a low-noise front-end amplifier (RX), and a complementary-metal-oxide-semiconductor, aluminum nitride, piezoelectric micromachined ultrasonic transducer (CMOS-AlN-PMUT). The system was designed using the 0.13-μm Silterra CMOS process and the MEMS-on-CMOS platform, which allowed for the implementation of an AlN PMUT on top of the CMOS-integrated circuit. The HV transmitter drives a column of six 80-μm-square PMUTs excited with 32 V in order to generate enough acoustic pressure at a 2.1-mm axial distance. On the reception side, another six 80-μm-square PMUT columns convert the received echo into an electric charge that is amplified by the receiver front-end amplifier. A comparative analysis between a voltage front-end amplifier (VA) based on capacitive integration and a charge-sensitive front-end amplifier (CSA) is presented. Electrical and acoustic experiments successfully demonstrated the functionality of the designed low-power analog front-end circuitry, which outperformed a state-of-the art front-end application-specific integrated circuit (ASIC) in terms of power consumption, noise performance, and area.

In this work, a waterproof tent-plate piezoelectric micromachined ultrasonic transducer (PMUT) with enhanced performance as actuator and sensor in comparison with standard clamped PMUT is presented. The squared AlN PMUT has four linear holes that are sealed by the passive layer allowing to increase the movement and giving the capability to work in liquid environment. The dimension of the holes was optimized to increase the PMUT displacement at least twice in relation with the regular clamped device. The acoustic performance of the PMUT was simulated in COMSOL Multiphysics and the results were experimentally verified under liquid operation. The experimental transmitting sensitivity, 3.9 kPa/V, as well as the sensor sensitivity, 13.4 V/MPa, provide a 2x factor improvement in contrast with the clamped PMUT with competitive values. Additionally, the presented tent-plate PMUT provides advantages in relation with the area, cost, power consumption and imaging quality thanks to the capability to be monolithically integrated over CMOS substrates.

In this paper, guidelines for the optimization of piezoelectrical micromachined ultrasound transducers (PMUTs) monolithically integrated over a CMOS technology are developed. Higher acoustic pressure is produced by PMUTs with a thin layer of AlN piezoelectrical material and Si₃N₄ as a passive layer, as is studied here with finite element modeling (FEM) simulations and experimental characterization. Due to the thin layers used, parameters such as residual stress become relevant as they produce a buckled structure. It has been reported that the buckling of the membrane due to residual stress, in general, reduces the coupling factor and consequently degrades the efficiency of the acoustic pressure production. In this paper, we show that this buckling can be beneficial and that the fabricated PMUTs exhibit enhanced performance depending on the placement of the electrodes. This behavior was demonstrated experimentally and through FEM. The acoustic characterization of the fabricated PMUTs shows the enhancement of the PMUT performance as a transmitter (with 5 kPa V⁻¹ surface pressure for a single PMUT) and as a receiver (12.5 V MPa⁻¹) in comparison with previously reported devices using the same MEMS-on-CMOS technology as well as state-of-the-art devices.

This paper presents a fully operational integrated ultrasound transceiver based on a single piezoelectric micromachined ultrasonic transducer (PMUT) monolithically fabricated with a 0.13 µm complementary metal oxide semiconductor (CMOS) analog front-end circuitry. The single PMUT-on-CMOS transducer produces ultrasound waves in liquid environment with competitive values, as actuator: 71 Pa*mm*V ⁻¹ as well as provides a high reception sensitivity (20 V/MPa). These two characteristics allow for an efficient single-pixel pulse-echo system. From time-of-flight experiments with this single PMUT-on-CMOS transceiver, a SNR dependence of 25 dB/z (z, axial distance) is achieved, allowing efficient pulse-echo imaging at 2 mm axial distances. These measurements demonstrate the capabilities of the single PMUT-on-CMOS transceivers for pixel sized acoustic imaging system. In this paper a full characterization of the single PMUT-on-CMOS transceiver is provided.

In this work we present an array of piezoelectric micromachined ultrasound transducer (PMUT’s) based on AlScN piezoelectric layer, monolithically integrated on top of a 130 nm CMOS circuit. The ${7}\times {7}$ array along with the analog-front-end circuit has been configured to work as a linear phased array. Experiments carried out have demonstrated the homogeneous PMUT’s behavior, showing a small dispersion in terms of frequency, bandwidth, and sensitivity. The feasibility of easily performing a transmission beam steering and focusing has been proven. In particular, the beam directivity has been characterized in terms of the width of the main lobe. The integrated CMOS analog-front-end allows the reduction of parasitic elements and noise, improving the signal to noise ratio (SNR). As a proof of concept, a B-mode image, with a 16 dB dynamic range, using a single ${7}\times {1}$ AlScN PMUT-on-CMOS channel as a receiver has been obtained.