This work demonstrates the design, fabrication, and characterization of the first piezoelectric micromachined ultrasonic transducers (PMUTs) based on bilayer X-cut lithium niobate (LiNbO3). A comparison of PMUT materials based on different figures of merit (FoMs) is presented, highlighting LiNbO3 as a promising and well-balanced alternative to more conventional materials. To leverage its superior material properties, PMUTs were designed based on bilayer X-cut LiNbO3 to fully harnesses the in-plane stress associated with the bending of the structure, thereby enhancing transduction. The fabricated devices show high electromechanical coupling (k2t ) of 4:6 %, albeit significantly lower than the simulated value due to parasitic effects. Mechanical vibration characterization shows a high static displacement of 0:88 nm=V and excellent linear dynamic range. Based on this design, an 8 × 1 array is demonstrated showing excellent consistency among the elements, with a frequency spread of 0:006 MHz and a displacement sensitivity spread of 0:15 nm=V. Our devices show comparable performance to monocrystalline PZT-based PMUTs, and substantially outperform ScAlN-based PMUTs in terms of static displacement sensitivity by a factor of 5. These results underscore the strong potential of LiNbO3 for high-performance PMUTs.

IN [1], there is a mistake in the timing diagram shown in Fig. 6. Switches S 1-S 4 are skipping some of the samples and the rate at which they are operating implies a TDM rate of 10 MHz, whereas (as described in [1]) this should be 20 MHz. In the updated Fig. 6, S 1-S 4 have been updated and a minor change has been made to the timing shown for switches Q₁ and Q₂, such that the correct TDM rate is indicated and no sample provided to the S/H stage via N1-N4 is skipped in the diagram. (Figure presented).

This work identifies the optimal orientation of lithium niobate (LiNbO3, LN) for piezoelectric micromachined ultrasonic transducers (PMUTs) operating in lateral-field excitation (LFE) and thickness-field excitation (TFE) modes. Geometry-independent material figures of merit (FoMs), representing the round-trip signal-to-noise ratio (SNR), are evaluated by sweeping rotated material tensors across the full orientation space. Finite element method (FEM) simulation is then used to quantify the electromechanical coupling k_t² under consistent device stacks and electrode layouts. The FoMs peak at 140°Y-cut LiNbO3 (≈120% of PZT-5H); the best commercial TFE option, 128°Y-cut, attains ~65% of that maximum. Under the shared baseline design, the highest k_t² is achieved with X-cut LiNbO3 (≈7.2%) using elongated rectangular membranes, about 70% of the PZT-5H reference. Our results provide clear design guidance for LiNbO3 PMUTs to maximize performance: optimal cut, in-plane rotation, and membrane geometry.

Emerging handheld and wearable ultrasound devices enable diagnosis and long-term monitoring outside clinical settings. They require a low-power, highly complex, locally integrated system to process the RF data. The analog-to-digital converter (ADC) is a critical building block in the receive chain of these systems as it enables digital beamforming and image reconstruction. However, the ADCs currently used in cart-based imaging systems are bulky and consume too much power to be integrated into battery-powered devices. This article investigates how the area and power consumption of the commonly used successive approximation register (SAR) ADC can be reduced without negatively affecting B-mode and color-Doppler image quality. A Monte Carlo (MC) simulation study was performed in which RF data acquired with a phased-array transducer in Field II were digitized using a model of a nonideal ADC. Five different nonidealities were applied to four commonly used SAR-ADC architectures. B-mode and color-Doppler images were reconstructed from the digitized RF data. The impact of the nonidealities on the image quality was evaluated by means of three image quality metrics (IQM): peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and contrast-to-noise ratio (CNR). The effectiveness of error correction and ways of calibration are also discussed. The results show that both B-mode imaging and color-Doppler imaging are inherently resilient to nonidealities, particularly capacitor mismatch, leading to relaxed ADC requirements and paving the way for more practical in-probe digitization.

Objective: Described here is the development of an ultrasound matrix transducer prototype for high-frame-rate 3-D intra-cardiac echocardiography. Methods: The matrix array consists of 16 × 18 lead zirconate titanate elements with a pitch of 160 µm × 160 µm built on top of an application-specific integrated circuit that generates transmission signals and digitizes the received signals. To reduce the number of cables in the catheter to a feasible number, we implement subarray beamforming and digitization in receive and use a combination of time-division multiplexing and pulse amplitude modulation data transmission, achieving an 18-fold reduction. The proposed imaging scheme employs seven fan-shaped diverging transmit beams operating at a pulse repetition frequency of 7.7 kHz to obtain a high frame rate. The performance of the prototype is characterized, and its functionality is fully verified. Results: The transducer exhibits a transmit efficiency of 28 Pa/V at 5 cm per element and a bandwidth of 60% in transmission. In receive, a dynamic range of 80 dB is measured with a minimum detectable pressure of 10 Pa per element. The element yield of the prototype is 98%, indicating the efficacy of the manufacturing process. The transducer is capable of imaging at a frame rate of up to 1000 volumes/s and is intended to cover a volume of 70° × 70° × 10 cm. Conclusion: These advanced imaging capabilities have the potential to support complex interventional procedures and enable full-volumetric flow, tissue, and electromechanical wave tracking in the heart.

This article presents an application-specific integrated circuit (ASIC) for catheter-based 3-D ultrasound imaging probes. The pitch-matched design implements a comprehensive architecture with high-voltage (HV) transmitters, analog front ends, hybrid beamforming analog-To-digital converters (ADCs), and data transmission to the imaging system. To reduce the number of cables in the catheter while maintaining a small footprint per element, transmission (TX) beamforming is realized on the chip with a combination of a shift register (SR) and a row/column (R/C) approach. To explore an additional cable-count reduction in the receiver part of the design, a channel with a combination of time-division multiplexing (TDM), subarray beamforming, and multi-level pulse amplitude modulation (PAM) data transmission is also included. This achieves an 18-fold cable-count reduction and minimizes the power consumption in the catheter by a load modulation (LM) cable driver. It is further explored how common-mode interference can limit beamforming gain and a strategy to reduce its impact with local regulators is discussed. The chip was fabricated in TSMC 0.18-m HV BCD technology and a 2-D PZT transducer matrix of 16 × 18 elements with a pitch of 160 m and a center frequency of 6 MHz was manufactured on the chip. The system can generate all required TX patterns at up to 30 V, provides quick settling after the TX phase, and has an reception (RX) power consumption of only 1.12 mW/element. The functionality and operation of up to 1000 volumes/s have been demonstrated in electrical and acoustic imaging experiments.

While medical imaging using ultrasound is an established field, technical advances are enabling a range of new-use cases and associated new ultrasound imaging devices. Examples include catheters capable of providing real-time 3D images to guide minimally invasive interventions and wearable devices for new monitoring and diagnostic applications. In contrast with conventional probes, which contain little or no electronics, these new devices need to become “smart”: integrated circuits need to be integrated into the probe to interface in a pitch-matched fashion with the many transducer elements (typically 1000+) needed for real-time 3D imaging. This chapter discusses the challenges associated with the design of such pitch-matched integrated circuits, focusing on strategies for channel-count reduction, beamforming, and digitization. The chapter includes a case study of a state-of-the-art catheter-based design for high-frame-rate 3D intracardiac imaging.

This article presents a pitch-matched transceiver application-specific integrated circuit (ASIC) for a wearable ultrasound device intended for transfontanelle ultrasonography, which includes element-level 20-V unipolar pulsers with transmit (TX) beamforming, and receive (RX) circuitry that combines eightfold multiplexing, four-channel micro-beamforming (?BF), and subgroup-level digitization to achieve an initial 32-fold channel-count reduction. The ?BF is based on passive boxcar integration, merged with a 10-bit 40 MS/s SAR ADC in the charge domain, thus obviating the need for explicit anti-alias filtering (AAF) and power-hungry ADC drivers. A compact and low-power reference generator employs an area-efficient MOS capacitor as a reservoir to quickly set a reference for the ADC in the charge domain. A low-power multi-level data link, based on 16-level pulse-amplitude modulation, concatenates the outputs of four ADCs, providing an overall 128-fold channel-count reduction. A prototype transceiver ASIC was fabricated in a 180-nm BCD technology, and interfaces with a 2-D PZT transducer array of 16 × 16 elements with a pitch of 125 ?m and a center frequency of 9 MHz. The ASIC consumes 1.83 mW/element. The data link achieves an aggregate 3.84 Gb/s data rate with 3.3 pJ/bit energy efficiency. The ASIC's functionality has been demonstrated through electrical, acoustic, and imaging experiments.

This article presents an application-specific integrated circuit (ASIC) for battery-powered ultrasound (US) devices. The ASIC implements a novel energy-efficient high-voltage (HV) pulser that generates HV transmit (TX) pulses directly from a low-voltage (LV) battery supply. By means of a single off-chip inductor, energy is supplied to a US transducer in a resonant fashion, directly generating half-period sinusoidal HV pulses on the transducer, while consuming substantially less energy than a conventional class-D pulser. By recycling residual reactive energy from the transducer back to the input, the energy consumption is further reduced by more than 50%. The autocalibration techniques are leveraged to deal with tolerances of the inductor, transducer, and battery supply and thus maximize the energy efficiency. A prototype chip was fabricated in TSMC 0.18-μm HV BCD technology and used to drive external 120-pF capacitive micromachined US transducers (CMUTs) with a center frequency of approximately 2.5 MHz. Electrical measurements show that the prototype can generate pulses with a peak amplitude between 10 and 30 V accurate to within ±1 V. Acoustic measurements demonstrate successful ultrasonic pulse transmission and pulse-echo measurements. The prototype reaches a peak efficiency of 0.23 fCV ² , which is the highest reported to date for HV pulsers targeting US imaging.

This paper presents a pitch-matched transceiver ASIC integrated with a 2-D transducer array for a wearable ultrasound device for transfontanelle ultrasonography. The ASIC combines 8-fold multiplexing, 4-channel micro-beamforming (μ BF) and sub-array-level digitization to achieve a 128-fold channel-count reduction. The μ BF is based on passive boxcar integration and interfaces with a 10-bit 40 MS/s SAR ADC in the charge domain, thus obviating the need for explicit anti-alias filtering and power-hungry ADC drivers. A compact and low-power reference generator employs an area-efficient MOS capacitor as a reservoir to quickly set a reference for the ADC in the charge domain. A low-power multi-level data link concatenates outputs of four ADCs, leading to an aggregate 3.84 Gb/s data rate. Per channel, the RX circuit consumes 2.06 mW and occupies 0.05 mm2.

This article presents a low-power and small-area transceiver application-specific integrated circuit (ASIC) for 3-D trans-fontanelle ultrasonography. A novel micro-beamforming receiver architecture that employs current-mode summation and boxcar integration is used to realize delay-and-sum on an N -element sub-array using N× fewer capacitive memory elements than conventional micro-beamforming implementations, thus reducing the hardware overhead associated with the memory elements. The boxcar integration also obviates the need for explicit anti-aliasing filtering in the analog front end, thus further reducing die area. These features facilitate the use of micro-beamforming in smaller pitch applications, as demonstrated by a prototype transceiver ASIC employing micro-beamforming on sub-arrays of N=4 elements, targeting a wearable ultrasound device that monitors brain perfusion in preterm infants via the fontanel. To meet its strict spatial resolution requirements, a 10-MHz 100- μ m-pitch piezoelectric transducer array is employed, leading to a per-element die area > 2 × smaller than prior designs employing micro-beamforming.

High frame rate three-dimensional (3D) ultrasound imaging would offer excellent possibilities for the accurate assessment of carotid artery diseases. This calls for a matrix transducer with a large aperture and a vast number of elements. Such a matrix transducer should be interfaced with an application-specific integrated circuit (ASIC) for channel reduction. However, the fabrication of such a transducer integrated with one very large ASIC is very challenging and expensive. In this study, we develop a prototype matrix transducer mounted on top of multiple identical ASICs in a tiled configuration. The matrix was designed to have 7680 piezoelectric elements with a pitch of 300 μm × 150 μm integrated with an array of 8 × 1 tiled ASICs. The performance of the prototype is characterized by a series of measurements. The transducer exhibits a uniform behavior with the majority of the elements working within the −6 dB sensitivity range. In transmit, the individual elements show a center frequency of 7.5 MHz, a −6 dB bandwidth of 45%, and a transmit efficiency of 30 Pa/V at 200 mm. In receive, the dynamic range is 81 dB, and the minimum detectable pressure is 60 Pa per element. To demonstrate the imaging capabilities, we acquired 3D images using a commercial wire phantom.

This article presents a compact analog front-end (AFE) circuit for ultrasound receivers with linear-in-dB continuous gain control for time-gain compensation (TGC). The AFE consists of two variable-gain stages, both of which employ a novel complementary current-steering network (CCSN) as the interpolator to realize continuously variable gain. The first stage is a trans-impedance amplifier (TIA) with a hardware-sharing inverter-based input stage to save power and area. The TIA's output couples capacitively to the second stage, which is a class-AB current amplifier (CA). The AFE is integrated into an application-specific integrated circuit (ASIC) in a 180-nm high-voltage BCD technology and assembled with a 100 μm-pitch PZT transducer array of 8 × 8 elements. Both electrical and acoustic measurements show that the AFE achieves a linear-in-dB gain error below ±0.4 dB within a 36-dB gain range, which is > 2 × better than the prior art. Per channel, the AFE occupies 0.025 mm2 area, consumes 0.8 mW power, and achieves an input-referred noise density of 1.31 pA/√Hz.

Intra-cardiac echography (ICE) probes (Fig. 32.2.1) are widely used in electrophysiology for their good procedure guidance and relatively safe application. ASICs are increasingly employed in these miniature probes to enhance signal quality and reduce the number of connections needed in mm-diameter catheters [1]-[5]. 3D visualization in real-time is additionally enabled by 2D transducer arrays with, for each transducer element, a high-voltage (HV) transmit (TX) part, to generate acoustic pulses of sufficient pressure, and a receive (RX) path, to process the resulting echoes. To achieve the required reduction in RX channels, micro-beamforming (BF), which merges the signals from a subarray using a delay-and-sum operation, has been shown to be an effective solution [3], [4]. However, due to the frame-rate reduction that is associated with BF, these designs cannot serve emerging high-frame-rate imaging modes (1000 volumes/s) like 3D blood-flow and elastography imaging. In-probe digitization has recently been investigated to provide further channel-count reduction, make data transmission more robust, and enable pre-processing in the probe [1]-[3]. However, these earlier designs have either no TX functionality [2], [3] or only low-voltage (LV) TX [1] integrated. Combining BF and digitization with area-hungry HV transmitters in a pitch-matched scalable fashion while supporting high-frame-rate imaging remains an unmet challenge. The work presented in this paper meets this target, enabled by a hybrid ADC, the small die size of which allows for co-integration with 65V element-level pulsers.

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is normally treated by RF ablation. Intracardiac echography (ICE) is widely employed during RF ablation procedures to guide the electrophysiologist in navigating the ablation catheter, although only 2-D probes are currently clinically used. A 3-D ICE catheter would not only improve visualization of the atrium and ablation catheter, but it might also provide the 3-D mapping of the electromechanical wave (EW) propagation pattern, which represents the mechanical response of cardiac tissue to electrical activity. The detection of this EW needs 3-D high-frame-rate imaging, which is generally only realizable in tradeoff with channel count and image quality. In this simulation-based study, we propose a high volume rate imaging scheme for a 3-D ICE probe design that employs 1-D micro-beamforming in the elevation direction. Such a probe can achieve a high frame rate while reducing the channel count sufficiently for realization in a 10-Fr catheter. To suppress the grating-lobe (GL) artifacts associated with micro-beamforming in the elevation direction, a limited number of fan-shaped beams with a wide azimuthal and narrow elevational opening angle are sequentially steered to insonify slices of the region of interest. An angular weighted averaging of reconstructed subvolumes further reduces the GL artifacts. We optimize the transmit beam divergence and central frequency based on the required image quality for EW imaging (EWI). Numerical simulation results show that a set of seven fan-shaped transmission beams can provide a frame rate of 1000 Hz and a sufficient spatial resolution to visualize the EW propagation on a large 3-D surface.