Anshuman Bhuyan

Optimized Circuit Failure Prediction for Aging: Practicality and Promise

Circuit failure prediction is used to predict occurrences of circuit failures, during system operation, before errors appear in system data and states. This technique is applicable for overcoming major scaled-CMOS reliability challenges posed by aging mechanisms such as Negative-Bias-Temperature-Instability (NBTI). This is possible because of the gradual nature of degradation associated with such aging mechanisms. Circuit failure prediction uses special on-chip circuits called aging sensors. In this paper, we experimentally demonstrate correct functionality and practicality of two flavors of flip-flop designs with built-in aging sensors using 90 nm test chips. We also present an aging-aware timing analysis technique to strategically place such flip-flops with built-in aging sensors at selective locations inside a chip for effective circuit failure prediction. This aging-aware timing analysis approach also minimizes the chip-level area impact of such aging sensors. Results from two 90 nm designs demonstrate the practicality and effectiveness of optimized circuit failure prediction with overall chip-level area impact of 2.5% and 0.6%.

Integrated Circuits for Volumetric Ultrasound Imaging With 2-D CMUT Arrays

Real-time volumetric ultrasound imaging systems require transmit and receive circuitry to generate ultrasound beams and process received echo signals. The complexity of building such a system is high due to requirement of the front-end electronics needing to be very close to the transducer. A large number of elements also need to be interfaced to the back-end system and image processing of a large dataset could affect the imaging volume rate. In this work, we present a 3-D imaging system using capacitive micromachined ultrasonic transducer (CMUT) technology that addresses many of the challenges in building such a system. We demonstrate two approaches in integrating the transducer and the front-end electronics. The transducer is a 5-MHz CMUT array with an 8 mm × 8 mm aperture size. The aperture consists of 1024 elements (32 × 32) with an element pitch of 250 μm. An integrated circuit (IC) consists of a transmit beamformer and receive circuitry to improve the noise performance of the overall system. The assembly was interfaced with an FPGA and a back-end system (comprising of a data acquisition system and PC). The FPGA provided the digital I/O signals for the IC and the back-end system was used to process the received RF echo data (from the IC) and reconstruct the volume image using a phased array imaging approach. Imaging experiments were performed using wire and spring targets, a ventricle model and a human prostrate. Real-time volumetric images were captured at 5 volumes per second and are presented in this paper.

3D volumetric ultrasound imaging with a 32×32 CMUT array integrated with front-end ICs using flip-chip bonding technology

3D ultrasound imaging is becoming increasingly prevalent in the medical field. Compared to conventional 2D imaging systems, 3D imaging can provide a detailed view of tissue structures that makes diagnosis easier for the physicians. In addition, 2D image slices can be formed at various orientations to the transducer, making the examination less dependent on the skill of the sonographer. However, various challenges exist in developing a 3D imaging system, such as integration of a large number of elements, as well as post-processing of datasets received from a large number of channels. 2D transducer arrays are typically integrated with custom ICs in the probe handle to perform some intermediate beamforming and to reduce the number of cable connections to the imaging system. Capacitive micromachined ultrasonic transducers (CMUTs) have emerged as an alternative to piezoelectric transducers. Being a MEMS device, they greatly benefit from flexibility and ease of fabrication, and can be seamlessly integrated with electronics. Previous work demonstrates 3D stacking of CMUTs and dummy ICs with an intermediate interposer layer. However, that represents more of a mechanical demonstration of 3D integration. In this paper, we present a fully functional 3D ultrasound imaging system comprising a 32×32 2D CMUT array, 3D-stacked with front-end ICs using flip-chip bonding technology. The imaging system is capable of capturing real-time volumetric ultrasound data, and displaying 2D and 3D ultrasound images.

Non-contact thermoacoustic detection of embedded targets using airborne-capacitive micromachined ultrasonic transducers

A radio frequency (RF)/ultrasound hybrid imaging system using airborne capacitive micromachined ultrasonic transducers (CMUTs) is proposed for the remote detection of embedded objects in highly dispersive media (e.g., water, soil, and tissue). RF excitation provides permittivity contrast, and ultra-sensitive airborne-ultrasound detection measures thermoacoustic-generated acoustic waves that initiate at the boundaries of the embedded target, go through the medium-air interface, and finally reach the transducer. Vented wideband CMUTs interface to 0.18 μm CMOS low-noise amplifiers to provide displacement detection sensitivity of 1.3 pm at the transducer surface. The carefully designed vented CMUT structure provides a fractional bandwidth of 3.5% utilizing the squeeze-film damping of the air in the cavity.

Real-time volumetric imaging system for CMUT arrays

We designed and implemented a flexible real-time volumetric ultrasound imaging system for capacitive micromachined ultrasonic transducer (CMUT) arrays, consisting of an ultrasound data acquisition system, an FPGA board, and a host PC. The system works with arbitrary-shaped CMUT arrays and non-standard beamforming methods, as well as with regular-shaped CMUT arrays and conventional beamforming methods. In this paper, we present the system design and real-time imaging results obtained using this system with a ring array, a rectangular array, and a linear array. In synthetic phased array (SPA) imaging with a 64-element ring array, we could display 3 image planes with a total of about 70,000 pixels in real time, at a frame rate of 9 frames per second (fps) which was limited by the computational load on the CPU required for synthetic beamforming. On the other hand, the frame rate in classic phased array (CPA) imaging is limited by the data transfer time. In CPA imaging with a 16×16-element rectangular array, a frame rate of 5.4 fps was achieved for 1,250 acquisitions per frame and a 2.5-cm imaging depth. The frame rate can be increased by reducing the number of pixels processed in SPA, or by reducing the number of beams received in CPA, at the expense of degraded image quality or reduced field of view.

An integrated Ring CMUT array for endoscopic ultrasound and photoacoustic imaging

This work presents our preliminary results on developing an integrated quad-ring CMUT array for endoscopic ultrasound and photoacoustic imaging. We have designed and fabricated a ring capacitive micromachined ultrasonic transducer (CMUT) array composed of 512 elements distributed among four concentric rings each having 128 elements. The operational frequency of each ring was chosen to achieve a similar pressure beam profile for all the rings. The devices inner and outer diameters measure 5.0 and 10.1 mm, respectively. The CMUT array was integrated with custom front-end ICs using a quartz fan-out board. This bench-top assembly allowed connection to a single ring (i.e., 128 elements) at a time. Thus far, we have built assemblies with connections to the two outer rings. We have successfully demonstrated real-time volumetric imaging with these assemblies using nylon wire phantom and metal spring phantom.

Dual-mode integrated circuit for imaging and HIFU with 2-D CMUT arrays

Successful high intensity focused ultrasound (HIFU) operation requires a reliable guidance and monitoring method such as magnetic resonance imaging (MRI) or ultrasound imaging. However, both widely used modalities are typically separate from the HIFU system, which makes co-registration of HIFU with cross-sectional imaging difficult. In this paper, we present a dual-mode integrated circuit (IC) that can perform both ultrasound imaging and HIFU with a single 2D capacitive micromachined ultrasonic transducer (CMUT) array, combining these two systems for ease of use. The dual-mode IC consists of pulsers, transmit beamforming circuitry, and low-noise amplifiers for imaging mode and switches for HIFU mode. By turning this switching network on and off, the system can alternately operate the imaging mode and HIFU mode on demand. The dual-mode IC was designed and fabricated in the 0.18-μm HV 4LM process provided by Maxim Inc. We fabricated a 32×32-element CMUT array that has a center frequency of 5 MHz using a sacrificial release process and flip-chip bonded this CMUT array to the IC. With the back-end system, real-time volumetric imaging on the wire phantom and HIFU ablation on ex-vivo tissue were performed respectively.

Ex Vivo HIFU Experiments Using a

High-intensity focused ultrasound (HIFU) has been used as noninvasive treatment for various diseases. For these therapeutic applications, capacitive micromachined ultrasonic transducers (CMUTs) have advantages that make them potentially preferred transducers over traditional piezoelectric transducers. In this paper, we present the design and the fabrication process of an 8×8-mm2, 32×32-element 2-D CMUT array for HIFU applications. To reduce the system complexity for addressing the 1024 transducer elements, we propose to group the CMUT array elements into eight HIFU channels based on the phase delay from the CMUT element to the targeted focal point. Designed to focus at an 8-mm depth with a 5-MHz exciting frequency, this grouping scheme was realized using a custom application-specific integrated circuit (ASIC). With a 40-V DC bias and a 60-V peak-to-peak AC excitation, the surface pressure was measured 1.2 MPa peak-to-peak and stayed stable for a long enough time to create a lesion. With this DC and AC voltage combination, the measured peak-to-peak output pressure at the focus was 8.5 MPa, which is expected to generate a lesion in a minute according to the temperature simulation. Following ex-vivo tissue experiments successfully demonstrated its capability to make lesions in both bovine muscle and liver tissue.

32 \times 32

Real-time 3D volumetric ultrasound imaging systems require transmit and receive circuitry to generate the ultrasound beam and process the received echo signals. Since a 2D array is required for 3D imaging, the complexity of building such a system is significantly higher, e.g., front-end electronics need to be interfaced to the transducer, a large number of elements need to be interfaced to the backend system and a large dataset needs to be processed. In this work, we present a 3D imaging system using capacitive micromachined ultrasonic transducer (CMUT) technology that addresses many of the challenges in building such a system. The transducer is a 5-MHz CMUT array with an 8 mm × 8 mm aperture size. The aperture consists of 1024 elements (32×32) with an element pitch of 250 μm. An integrated circuit (IC) is integrated very close to the CMUT array. It consists of a transmit beamformer and receive circuitry to improve the noise performance of the overall system. Simultaneous multi-beam transmit is also incorporated in the IC to improve the imaging frame rate. The CMUT is flip-chip bonded to the IC and the final assembly measured 9.2 mm × 9.2 mm. The assembly was then interfaced with an FPGA and a backend system (comprising of a data acquisition system and PC). The FPGA provided the digital I/O signals for the IC and the backend system was used to process the received RF echo data (from the IC) and reconstruct the volume image using a phased array imaging approach. Imaging experiments were performed using wire phantoms. Real-time volumetric images were captured at 5 volumes per second and are presented in this paper.

-Element CMUT Array

There are several applications in the medical field that require periodic monitoring of blood vessels or organ functions. Ultrasound, being one of the preferred imaging modalities, is often used for such applications. However, present day ultrasound probes are bulky and inconvenient. We present a low profile, wearable ultrasound probe that can be taped onto the patients body for periodic or constant monitoring of organ functions. The small form factor is key for such applications. Therefore, CMUT technology is ideal for development of such probes. The probe consists of a 64-element 1D linear array CMUT operating at 5 MHz. Front-end electronics were integrated with the CMUT to improve the SNR of the acquired image. The final assembly measures 6 cm × 3.5 cm × 0.35 cm. A PDMS lens lay on top of the assembly to allow focusing in the elevation plane. The probe is interfaced to a backend system (Verasonics data acquisition system, Verasonics, Inc., Redmond, WA). Verasonics provides the high voltage pulses and also digitizes the received RF echo data for image reconstruction. Field characterization of the probe was performed using a calibrated hydrophone and was compared to Field II simulations. Finally, imaging experiments were performed on a commercially available phantom as well as the human neck. Images were also acquired with a commercially available probe for the sake of comparison. The CMUT probe provided with comparable image quality to that of the commercial probe. Real time images were also acquired by the CMUT probe at 30 frames per second.