Federico Mazza

Imperial College London

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Timothy G. Constandinou

Imperial College London

Peilong Feng

Imperial College London

Katarzyna M. Szostak

Proton (United Kingdom)

Callum Lamont

University College London

Nick Donaldson

University College London

Kambiz Nanbakhsh

Delft University of Technology

Csaba Dücső

Centre for Energy Research

Ahmad Shah Idil

University College London

Kinga Tóth

HUN-REN Research Centre for Natural Sciences

ÖC

Ömer Can Akgun

Delft University of Technology

Cooperative Institutions

Imperial College London

University College London

Hungarian Academy of Sciences

HUN-REN Research Centre for Natural Sciences

Pázmány Péter Catholic University

NIHR Imperial Biomedical Research Centre

Delft University of Technology

BioElectronics (United States)

Institute of Cognitive Neuroscience and Psychology

Hungarian Research Network

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A Bayesian Demonstration of Reliability for Encapsulated Implanted Electronics

Callum Lamont Federico Mazza Nick Donaldson

The long term performance of implanted medical devices is critically affected by their packaging materials. Traditional hermetic enclosures are a hindrance to miniaturisation which might be avoided by polymer encapsulation. However, much uncertainty remains regarding such an approach for chronic implants. It is difficult to extract meaning from lifetime experiments performed on arbitrary test structures and before many highly reliable devices have actually failed. In this study, we describe an accelerated aging experiment on devices that employ test structures fabricated on a silicone encapsulated 0.35 μm CMOS technology. Samples are aged at 47, 67 and 87 °C under a constant 5V DC bias. After over 300 days of aging, of the 36 samples under test, there have only been four failures. Three failures are attributed to the interconnect to the measurement system, with the remaining failure due to delamination of the silicone encapsulant over wirebonds. By employing a Bayesian reliability analysis of the near-zero failure data we demonstrate a 1 ^st failure percentile for the CMOS components of greater than 92 days when aged at 87 °C, calculated at a 95% confidence level, which approximately corresponds to over 8 years at 37 °C.

10.1109/ner.2019.8717034

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On the longevity and inherent hermeticity of silicon-ICs: evaluation of bare-die and PDMS-coated ICs after accelerated aging and implantation studies

Nature Communications (2025)

Kambiz Nanbakhsh Ahmad Shah Idil Callum Lamont Csaba Dücső Ömer Can Akgun

Abstract Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for chronic use. Here, we evaluate the inherent hermeticity of bare die ICs, and examine the potential of polydimethylsiloxane (PDMS), a moisture-permeable elastomer, as a standalone encapsulation material. For this aim, the electrical and material performance of ICs sourced from two foundries was evaluated through one-year accelerated in vitro and in vivo studies. ICs featured custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated “bare die” and “PDMS-coated”. During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results revealed stable electrical performance, indicating the unaffected operation of ICs even when directly exposed to physiological fluids. Despite this, material analysis revealed IC degradation in the bare regions. PDMS-coated regions, however, revealed limited degradation, making PDMS a suitable IC encapsulant for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, broadening their applications in the biomedical field.

Polydimethylsiloxane

Bioelectronics

10.1038/s41467-024-55298-4

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Citations (1)

Autonomous SoC for Neural Local Field Potential Recording in mm-Scale Wireless Implants

2022 IEEE International Symposium on Circuits and Systems (ISCAS) (2018)

Lieuwe B. Leene Michal Maslik Peilong Feng Katarzyna M. Szostak Federico Mazza

Next generation brain machine interfaces fundamentally need to improve the information transfer rate and chronic consistency when observing neural activity over a long period of time. Towards this aim, this paper presents a novel System-on-Chip (SoC) for a mm-scale wireless neural recording node that can be implanted in a distributed fashion. The proposed self-regulating architecture allows each implant to operate autonomously and adaptively load the electromagnetic field to extract a precise amount of power for full-system operation. This can allow for a large number of recording sites across multiple implants extending through cortical regions without increased control overhead in the external head-stage. By observing local field potentials (LFPs) only, chronic stability is improved and good coverage is achieved whilst reducing the spatial density of recording sites. The system features a ΔΣ based instrumentation circuit that digitises high fidelity signal features at the sensor interface thereby minimising analogue resource requirements while maintaining exceptional noise efficiency. This has been implemented in a 0.35 μm CMOS technology allowing for wafer-scale post-processing for integration of electrodes, RF coil, electronics and packaging within a 3D structure. The presented configuration will record LFPs from 8 electrodes with a 825 Hz bandwidth and an input referred noise figure of 1.77μVrms. The resulting electronics has a core area of 2.1 mm ² and a power budget of 92 μW

Local field potential

10.1109/iscas.2018.8351147

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Citations (19)

Quantum Fischer information in a strange metal

arXiv (Cornell University) (2024)

Federico Mazza Sounak Biswas Xinlin Yan A. V. Prokofiev P. Steffens

A strange metal is an exotic state of correlated quantum matter; intensive efforts are ongoing to decipher its nature. Here we explore whether the quantum Fisher information (QFI), a concept from quantum metrology, can provide new insight. We use inelastic neutron scattering and quantum Monte Carlo simulations to study a Kondo destruction quantum critical point, where strange metallicity is associated with fluctuations beyond a Landau order parameter. We find that the QFI probed away from magnetic Bragg peaks, where the effect of magnetic ordering is minimized, increases strongly and without a characteristic scale as the strange metal forms with decreasing temperature, evidencing its unusual entanglement properties. Our work opens a new direction for studies across strange metal platforms.

10.48550/arxiv.2403.12779

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Author Correction: On the longevity and inherent hermeticity of silicon-ICs: evaluation of bare-die and PDMS-coated ICs after accelerated aging and implantation studies

Nature Communications (2025)

Kambiz Nanbakhsh Ahmad Shah Idil Callum Lamont Csaba Dücső Ömer Can Akgun

10.1038/s41467-025-57175-0

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Microwire-CMOS integration of mm-scale neural probes for chronic local field potential recording

2022 IEEE Biomedical Circuits and Systems Conference (BioCAS) (2017)

Katarzyna M. Szostak Federico Mazza Michal Maslik Lieuwe B. Leene Peilong Feng

This paper proposes a novel method for integrating CMOS microelectronics with microwire-based electrodes for next generation implantable brain machine interfaces. There is strong evidence to suggest that microwire-based electrodes outperform micromachined and polymer-based electrodes in terms of signal integrity and chronic viability. Furthermore, it has been shown that the recording of Local Field Potentials (LFPs) is more robust to tissue damage and scar tissue growth when compared to action potentials. This work therefore investigates the suitability of microwire electrodes for LFP recording by studying the electrical properties of key materials. We identify Niobium (Nb) as a candidate material with highly desirable properties. There is however also an inherent incompatibility when it comes to connection of microwire-based electrodes to silicon chips. Here we present a new process flow utilising a recessed glass substrate for mechanical support, silicon interposer for interconnection, and electroplating for contact adhesion. Furthermore, the proposed structure lends itself to hermetic encapsulation towards gas cavity based micropackages.

Microelectronics

10.1109/biocas.2017.8325185

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Integrated Devices for Micro-Package Integrity Monitoring in mm-Scale Neural Implants

2022 IEEE Biomedical Circuits and Systems Conference (BioCAS) (2018)

Federico Mazza Yan Liu Nick Donaldson Timothy G. Constandinou

Recent developments in the design of active implantable devices have achieved significant advances, for example, an increased number of recording channels, but too often practical clinical applications are restricted by device longevity. It is important however to complement efforts for increased functionality with translational work to develop implant technologies that are safe and reliable to be hosted inside the human body over long periods of time. This paper first examines techniques currently used to evaluate micro-package hermeticity and key challenges, highlighting the need for new, in situ instrumentation that can monitor the encapsulation status over time. Two novel circuits are then proposed to tackle the specific issue of moisture penetration inside a sub-mm, silicon-based package. They both share the use of metal tracks on the different layers of the CMOS stack to measure changes in impedance caused by moisture present in leak cracks or diffused into the oxide layers.

10.1109/biocas.2018.8584761

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Citations (3)

Distributed Neural Interfaces: Challenges and Trends in Scaling Implantable Technology

Handbook of Neuroengineering (2023)

Katarzyna M. Szostak Peilong Feng Federico Mazza Timothy G. Constandinou

Current implantable neural interfaces, both clinically available solutions and research tools, rely on a limited number of implanted devices (from one to few units). This factor, aside from the obvious spatial resolution limitations, does not conform to the paradigm of the brain as a massively parallel computational system and creates a bottleneck in the amount of information that could be exchanged between the brain and an external processing unit. This issue has fuelled recent research efforts towards the study of distributed neural interfaces, systems that depend on a network of implanted nodes. Such configuration allows to spread of the overall complexity across multiple devices, which can now be more easily scaled down in size and individual power consumption, improving their conformity with the surrounding tissue, which is a major concern in current monolithic solutions. However, this architecture brings a new set of challenges ranging from the optimization of ultra-low-power electronics, through the formulation of a wireless transmission scheme for efficient power delivery and data transfer to the investigation of novel materials and methods for the fabrication of micro-scale, long-term reliable implants. This chapter outlines state of the art and describes design considerations for the future autonomous, wireless distributed neural implants. Aspects of miniaturization and chronic stability of devices including materials choice, implantation procedure, packaging strategies and microelectrode types are described, alongside a discussion on different modalities to achieve wireless power transfer and data telemetry.

Brain implant

10.1007/978-981-16-5540-1_11

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Longevity of Implantable Silicon-ICs for Emerging Neural Applications: Evaluation of Bare Die and PDMS-Coated ICs After Accelerated Aging and Implantation Studies

bioRxiv (Cold Spring Harbor Laboratory) (2024)

Kambiz Nanbakhsh Ahmad Shah Idil Callum Lamont Csaba Dücső Ömer Can Akgun

Abstract Silicon integrated circuits (ICs) are central to the next-generation miniature active neural implants, whether packaged in soft polymers for flexible bioelectronics or implanted as bare die for neural probes. These emerging applications bring the IC closer to the corrosive body environment, raising reliability concerns, particularly for long-term clinical use. Here, we evaluated the long-term electrical and material stability of silicon-ICs from two foundries, after one-year accelerated in vitro and in vivo animal studies. The ICs featured various custom-designed test structures and were partially PDMS coated, creating two regions on each chip, uncoated “bare die” and “PDMS-coated”. During the accelerated in vitro study, ICs were electrically biased and periodically monitored. Results demonstrated stable electrical performance for at least a year, suggesting that bare die ICs can function in the body for months. Despite electrical stability, material analysis revealed chemical and electrically driven degradation of the IC passivation in the bare die regions. In contrast, PDMS-coated regions revealed no such degradation, making PDMS a highly suitable encapsulant for ICs intended for years-long implantation. Based on the new insights, guidelines are proposed that may enhance the longevity of implantable ICs, significantly broadening their applications in the biomedical field.

Accelerated aging

10.1101/2024.03.06.583769

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Towards a Distributed, Chronically-Implantable Neural Interface

Nur Ahmadi Matthew L. Cavuto Peilong Feng Lieuwe B. Leene Michal Maslik

We present a platform technology encompassing a family of innovations that together aim to tackle key challenges with existing implantable brain machine interfaces. The ENGINI (Empowering Next Generation Implantable Neural Interfaces) platform utilizes a 3-tier network (external processor, cranial transponder, intracortical probes) to inductively couple power to, and communicate data from, a distributed array of freely-floating mm-scale probes. Novel features integrated into each probe include: (1) an array of niobium microwires for observing local field potentials (LFPs) along the cortical column; (2) ultra-low power instrumentation for signal acquisition and data reduction; (3) an autonomous, self-calibrating wireless transceiver for receiving power and transmitting data; and (4) a hermetically-sealed micropackage suitable for chronic use. We are additionally engineering a surgical tool, to facilitate manual and robot-assisted insertion, within a streamlined neurosurgical workflow. Ongoing work is focused on system integration and preclinical testing.

Interface (matter)

Transceiver

Instrumentation

10.1109/ner.2019.8716998

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Citations (52)