New Insights Into the I/V Hysteretic Characteristics of Memristive Biosensors

K. Bhardwaj; A. Golparvar; J. Chen; G. L. Barbruni; S. Carrara

Over the past decade, significant advancements have been made in the study of silicon nanowires (SiNWs). These nanoscaled devices can exhibit a memristive type of hysteresis in the current/voltage (I/V) plane that has been utilized in the biosensors leading to exceptional sensitivities up to the femto levels. Here we investigate the memristive properties of SiNW-based biosensors in their unmodified state, as well as after surface biofunctionalization with aptamers. The development of SiNWs involved a top-down nanofabrication approach, resulting in nanowires with 100 nm wide and 1 mu m long. Later, biofunctionalization was performed through controlled drop casting. The experimental findings obtained in this study demonstrate for the first time that different SiNWs from the same fabrication batch can exhibit diverse memristive switching phenomena in the I/V plane. These phenomena encompass both volatile noncrossing memristive behavior as well as nonvolatile crossing memristive responses. Furthermore, we demonstrate that the I/V hysteresis exhibited by biofunctionalized nanowires is determined by their inherent memristive characteristics and the induced capacitive effect. Drawing upon these new findings, a simple mathematical simulation model of the Memristive biosensor is developed and evaluated in SPICE.

DOI : 10.1109/LSENS.2023.3301840

Changes Over Time in the Electrode/Brain Interface Impedance: An Ex-Vivo Study

L. Iannucci; G. L. Barbruni; D. Ghezzi; M. Parvis; S. Grassini  et al.

Closed-loop neural implants based on continuous brain activity recording and intracortical microstimulation are extremely effective and promising devices to monitor and address many neurodegenerative diseases. The efficiency of these devices depends on the robustness of the designed circuits which rely on precise electrical equivalent models of the electrode/brain interface. This is true in the case of amplifiers for differential recording, voltage or current drivers for neurostimulation, and potentiostats for electrochemical bio-sensing. This is of paramount importance, especially for the next generation of wireless and ultra-miniaturised CMOS neural implants. Circuits are usually designed and optimized considering the electrode/brain impedance with a simple electrical equivalent model whose parameters are stationary over time. However, the electrode/brain interfacial impedance varies simultaneously in frequency and in time after implantation. The aim of this study is to monitor the impedance changes occurring on microelectrodes inserted in ex-vivo porcine brains to derive an opportune electrode/brain model describing the system and its evolution in time. In particular, impedance spectroscopy measurements have been performed for 144 hours to characterise the evolution of the electrochemical behaviour in two different setups analysing both the neural recording and the chronic stimulation scenarios. Then, different equivalent electrical circuit models have been proposed to describe the system. Results showed a decrease in the resistance to charge transfer, attributed to the interaction between biological material and the electrode surface. These findings are crucial to support circuit designers in the field of neural implants.

DOI : 10.1109/TBCAS.2023.3284691

A Front-End CMOS Interface Circuit With High Voltage Charge Pump and Oscillator for Capacitive Micromachined Ultrasonic Transducers

Y. Zhao; G. L. Barbruni; Z. Li; L. Zhao; X. Wang  et al.

Label-free biosensors, combined with miniaturized micro-electromechanical sensory platforms, offer an attractive solution for real-time and facile monitoring of biomolecules due to their high sensitivity and selectivity without the need for specifically labeling. Resonators have been acknowledged as an efficient technology for measuring biomolecular binding events including those involving nucleic acid and antibody. Among these, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as a promising candidate for biosensing. However, their usage is often limited by the requirement for high voltage supply and continuous frequency tracking, which can result in significant parasitic effects and measurement errors. In this brief, we present a novel front-end interface circuit for a CMUTs-based biosensor. The circuit, fabricated using TSMC 0.18-mu m BipolarCMOS-DMOS (BCD) technology, incorporates an on-chip high voltage charge pump and feedback frequency monitoring. The CMUTs array features 20 x 20 circular cells, fabricated using a low-temperature direct bonding technology, with an experimental parallel-resonant frequency of 1.724 MHz and a high quality factor of up to 40.9. To fit the measured electrical characteristics, a five-element equivalent lumped element model is proposed. The high voltage charge pump provides an output voltage of similar to 20 V, while the feedback oscillator has a ms-level start-up time and a total power dissipation of 3.8 mW. The proposed frontend interface is designed to function as a stand-alone chip for CMUTs-based resonant biodetection.

DOI : 10.1109/TCSII.2023.3261061

An Ultra-Miniaturised CMOS Clock and Data Recovery System for Wireless ASK Transmission

M. Cerbai; G. L. Barbruni; P. M. Ros; D. Demarchi; D. Ghezzi  et al.

Over the years, several clock and data recovery architectures have been proposed for wireless Amplitude Shift Keying (ASK) transmitted signals. State-of-the-art architectures mainly rely on synchronous phase-locked loop circuits or selfsampling systems, both resulting in large area consumption. This work presents a novel CMOS architecture for Clock and Data Recovery (CDR) in miniaturised and wirelessly powered implants. The proposed CDR architecture works at 433.92 MHz and includes: an ASK-demodulator, an on-chip oscillator, a power-on-reset, a control and a recovering block operating in feedback-loop. The ASK-demodulator works for a data rate as high as 6Mbps and a modulation index in the range of 9-30%. A novel communication protocol is presented for a separated clock and data transmission. The entire CDR architecture occupies 17 x 89 mu m(2) and consumes 15.01 mu W while operating with a clock rate of 6 Mbps.

A Novel Approach in Edge Computing: In-Memory Sensing of Cancer Markers

D. Heim; G. L. Barbruni; S. Carrara

We present here the first ever-reported direct computation of the cancer risk on cancer markers simultaneously detected by memristors. The novel approach in cancer diagnostics here proposed is based on the fusion of the three actions of sensing, computing and memory in a single-kind of device. So, this paper proposes the new concept of in-memory sensing as a disruptive approach in edge-computing. The concept is demonstrated by showing a well-known case in cancer diagnostics: the estimation of the risk of prostate cancer based on the simultaneous measure of Prostate Specific Antigen (PSA) and its Membrane isoform (PSMA).

Ultra-Miniaturised CMOS Current Driver for Wireless Biphasic Intracortical Microstimulation

G. L. Barbruni; P. M. Ross; D. Dernarchit; S. Carrara; D. Ghezzi

This work shows an ultra-miniaturised and ultra-low-power CMOS current driver for biphasic intracortical microstimulation. The CMOS driver is composed of a leakage-based voltage-to-current converter and an H-bridge circuit providing biphasic charge-balanced current stimulation. The circuit has been simulated, fabricated and tested. The current driver consumes 1.87 mu W with a supply voltage of 1.8 V, and it occupies a silicon area of 15X12.4 mu m(2) . The driver works in linearity in the current range between 23-92 mu A.

A 20 Mbps, 433 MHz RF ASK Transmitter to Inductively Power a Distributed Network of Miniaturised Neural Implants

G. L. Barbruni; F. Asti; P. M. Ros; D. Ghezzi; D. Demarchi  et al.

Simultaneous wireless information and power transfer is an emerging technique in neurotechnology. This work presents an efficient transmitter for both power transfer and downlink data communication to multiple, miniaturised and inductively-powered chips. We designed, implemented and tested a radio-frequency transmitter operating at 433.92 MHz of the industrial, scientific and medical band. A new structure is proposed to efficiently modulate the carrier, exploiting an amplitude-shift keying modulation reaching a data rate as high as 20 Mbps together with a variable modulation index as low as 8%.

Equivalent Circuit Analysis of CMUTs-based Device for Measurement in Liquid Samples

Y. Zhao; L. Zhao; G. L. Barbruni; Z. Li; Z. Jiang  et al.

Capacitive micromachined ultrasonic transducers (CMUTs) operating at the series and parallel resonant frequencies, have shown a great potential in ultrasonic application and in biodetection. However, previous equivalent circuits rarely consider the fitting performance and measurement. This study proposes the establishment of the simplified equivalent circuits for the CMUTs-based device to analyze the electrical properties and the measurement sensitivity in liquid environment. We simulate a circular CMUT cell both in air and water through finite element method via COMSOL software, exploiting the multi-domain coupling method. We analyze the impedance behaviors of the CMUTs array with 100 cells under different direct current bias voltages (2 - 10V). Simultaneously, we successfully investigate the damping effects on the electrical characteristics such as impedance, phase, and quality factor. With the 4-element Butterworth-vanDyke model, two simplified equivalent lumped element models (LEMs) are demonstrated to fit the impedance curves of the CMUTs array around the series and parallel frequencies, respectively. Additionally, the sensitivity is evaluated using the simplified equivalent LEMs to explore the CMUTs array has a high normalized measurement sensitivity of 6.024 ppb/Hz at the parallel frequency.

From 0.18 mu m to 28nm CMOS Down-scaling for Data Links in Body Dust Applications

G. L. Barbruni; S. Carrara; P. M. Ros; D. Demarchi

In this work, we study the effect of transistor downscaling in a wireless communication circuit for Body Dust application. The system requires a chip lateral size smaller than 10 mu m miming the typical size of a red blood cell and so, supporting free circulation in human tissues. Moreover, an ultra-low-power architecture is needed since the system is battery-less and wirelessly powered via acoustic power transfer. The aim of this paper is to present a data communication system for Body Dust systems, which works from the multiplexed sensor read-out front-end to the transmitter back-end taking account diagnostic information on different metabolite concentrations in human body. This work shows that scaling the architecture from a 0.18-mu m to 28-nm CMOS processes, it is possible to improve both size and power consumption. The improvement is about 40 times in size (2000 mu m(2) down to 50 mu m2) and two order of magnitude in average power consumption (10 mu W to cents of nW).

Miniaturised Wireless Power Transfer Systems for Neurostimulation: A Review

G. L. Barbruni; P. Motto Ros; D. Demarchi; S. Carrara; D. Ghezzi

In neurostimulation, wireless power transfer is an efficient technology to overcome several limitations affecting medical devices currently used in clinical practice. Several methods were developed over the years for wireless power transfer. In this review article, we report and discuss the three most relevant methodologies for extremely miniaturised implantable neurostimulator: ultrasound coupling, inductive coupling and capacitive coupling. For each powering method, the discussion starts describing the physical working principle. In particular, we focus on the challenges given by the miniaturisation of the implanted integrated circuits and the related ad-hoc solutions for wireless power transfer. Then, we present recent developments and progresses in wireless power transfer for biomedical applications. Last, we compare each technique based on key performance indicators to highlight the most relevant and innovative solutions suitable for neurostimulation, with the gaze turned towards miniaturisation.

DOI : 10.1109/TBCAS.2020.3038599