Developing ultrasensitive and CMOS compatible ISFETs in the BEOL of industrial UTBB FDSOI transistors

Le marché des capteurs a récemment connu une croissance spectaculaire alimentée par l'application remarquable de capteurs dans l'électronique de consommation, l'industrie de l'automatisation, les appareils portables, le secteur automobile et l'internet des objets de plus en plus adopté. La technologie avancée des complementary metal oxide semiconductor (CMOS), les technologies de nano et de micro-fabrication et les plateformes de synthèse de matériaux innovantes sont également des moteurs du développement incroyable de l'industrie des capteurs. Ces progrès ont permis la réalisation de capteurs dotés de nombreuses caractéristiques telles que la précision accrue, les dimensions miniaturisées, l’intégrabilité, la production de masse, le coût très réduit et le temps de réponse rapide. Les ion-sensitive field-effect transistors (ISFETs) sont des capteurs à l'état solide (bio) chimiques, destinés à la détection des ions H+ (pH), Na+ et K+. Malgré cela, la commercialisation des ISFETs est encore à ses balbutiements, après près de cinq décennies de recherche et développement. Cela est dû principalement à la sensibilité limitée, à la controverse sur l'utilisation de l'électrode de référence pour le fonctionnement des ISFETs et à des problèmes de stabilité. Dans cette thèse, les ISFETs ultrasensibles et compatibles CMOS sont intégrés dans le BEOL des transistors UTBB FDSOI standard. Un circuit diviseur capacitif est utilisé pour polariser la grille d’avant afin d'assurer des performances stables du capteur. En exploitant la fonction d’amplification intrinsèque fournie par les transistors UTBB FDSOI, nous avons présenté des ISFET ultra sensibles. L'amplification découle du fort couplage électrostatique entre la grille avant et la grille arrière du FDSOI et des capacités asymétriques des deux grilles. Un changement de tension au niveau de la grille avant apparaît sur la grille arrière sous la forme d'un décalage amplifié de la tension. L'amplification, représentée par le facteur de couplage (γ), est égale au rapport de la capacité de l'oxyde de grille et de la capacité de le buried oxide (BOX). Par conséquent, en fonctionnalisant la détection du pH sur la grille avant pour les dispositifs FDSOI, la modification du potentiel de surface sur la grille avant est détectée par la grille arrière et amplifiée du facteur de couplage (γ), donnant lieu à un capteur chimique à l'état solide à sensibilité ultra-élevée. L'intégration de la fonctionnalité de détection a été réalisée en back end of line (BEOL), ce qui offre les avantages d'une fiabilité et d'une durée de vie accrues du capteur, d'une compatibilité avec le processus CMOS standard et d'une possibilité d'intégration d'un circuit diviseur capacitif. Le fonctionnement des MOSFETs, sans une polarisation appropriée de la grille avant, les rend vulnérables aux effets de grilles flottantes indésirables. Le circuit diviseur capacitif résout ce problème en polarisant la grille avant tout enmaintenant la fonctionnalité de détection sur la même grille par un couplage capacitif au métal commun du BEOL. Par conséquent, le potentiel au niveau du métal BEOL est une somme pondérée du potentiel de surface au niveau de la grille de détection et de la polarisation appliquée au niveau de la grille de contrôle. Le capteur proposé est modélisé et simulé à l'aide de TCAD-Sentaurus. Un modèle mathématique complet a été développé. Il fournit la réponse du capteur en fonction du pH de la solution (entrée du capteur) et des paramètres de conception du circuit diviseur capacitif et du transistor UTBB FDSOI. Dans ce cas, des résultats cohérents ont été obtenus des travaux de modélisation et de simulation, avec une sensibilité attendue de 780 mV / pH correspondant à un film de détection ayant une réponse de Nernst. La modélisation et la simulation du capteur proposé ont également été validées par une fabrication et une caractérisation du capteur de pH à grille étendue avec validation de son concept. Ces capteurs ont été développés par un traitement séparé du composant de détection de pH, qui est connecté électriquement au transistor uniquement lors de la caractérisation du capteur. Ceci permet une réalisation plus rapide et plus simple du capteur sans avoir besoin de masques et de motifs par lithographie. Les capteurs à grille étendue ont présenté une sensibilité de 475 mV/pH, ce qui est supérieur aux ISFET de faible puissance de l'état de l’art. Enfin, l’intégration de la fonctionnalité de détection directement dans le BEOL des dispositifs FDSOI UTBB a été poursuivie. Une sensibilité expérimentale de 730 mV/pH a été obtenue, ce qui confirme le modèle mathématique et la réponse simulée. Cette valeur est 12 fois supérieure à la limite de Nernst et supérieure aux capteurs de l'état de l’art. Les capteurs sont également évalués pour la stabilité, la résolution, l'hystérésis et la dérive dans lesquels d'excellentes performances sont démontrées. Une nouvelle architecture de détection du pH est également démontrée avec succès, dans laquelle la détection est fonctionnalisée au niveau de la diode de protection de la grille plutôt que de la grille avant des dispositifs UTBB FDSOI. La commutation de courant abrupte, aussi basse que 9 mV/decade, pourrait potentiellement augmenter la sensibilité de polarisation fixée à 6,6 decade/pH. Nous avons démontré expérimentalement une sensibilité de 1,25 decade/pH supérieure à la sensibilité reportée à l’état de l’art.Abstract: The sensor market has recently seen a dramatic growth fueled by the remarkable application of sensors in the consumer electronics, automation industry, wearable devices, the automotive sector, and in the increasingly adopted internet of things (IoT). The advanced complementary metal oxide semiconductor (CMOS) technology, the nano and micro fabrication technologies, and the innovative material synthesis platforms are also driving forces for the incredible development of the sensor industry. These technological advancements have enabled realization of sensors with characteristic features of increased accuracy, miniaturized dimension, integrability, volume production, highly reduced cost, and fast response time. Ion-sensitive field-effect transistors (ISFETs) are solid state (bio)chemical sensors, for pH (H+), Na+, K+ ion detection, that are equipped with the promise of the highly aspired features of CMOS devices. Despite this, the commercialization of ISFETs is still at the stage of infancy after nearly five decades of research and development. This is due mainly to the limited sensitivity, the controversy over the use of the reference electrode for ISFET operation, and because of stability issues. In this thesis, ultrasensitive and CMOS compatible ISFETs are integrated in the back end of line (BEOL) of standard UTBB FDSOI transistors. A capacitive divider circuit is employed for biasing the front gate for stable performance of the sensor. Exploiting the intrinsic amplification feature provided by UTBB FDSOI transistors, we demonstrated ultrahigh sensitive ISFETs. The amplification arises from the strong electrostatic coupling between the front gate and the back gate of the FDSOI, and the asymmetric capacitances of the two gates. A change in voltage at the front gate appears at the back gate as an amplified shift in voltage. The amplification, referred to as the coupling factor (γ), is equal to the ratio of the gate oxide capacitance and the buried oxide (BOX) capacitance. Therefore, functionalizing the pH sensing at the front gate of FDSOI devices, the change in surface potential at the front gate is detected at the back gate amplified by the coupling factor (γ), giving rise to an ultrahigh-sensitive solid state chemical sensor. Integration of the sensing functionality was made in the BEOL which gives the benefits of increased reliability and life time of the sensor, compatibility with the standard CMOS process, and possibility for embedding a capacitive divider circuit. Operation of the MOSFETs without a proper front gate bias makes them vulnerable for undesired floating body effects. The capacitive divider circuit addresses these issues by biasing the front gate simultaneously with the sensing functionality at the same gate through capacitive coupling to a common BEOL metal. Therefore, the potential at the BEOL metal would be a weighted sum of the surface potential at the sensing gate and the applied bias at the control gate. The proposed sensor is modeled and simulated using TCAD-Sentaurus. A complete mathematical model is developed which provides the output of the sensor as a function of the solution pH (input to the sensor), and the design parameters of the capacitive divider circuit and the UTBB FDSOI transistor. In that case, consistent results have been obtained from the modeling and simulation works, with an expected sensitivity of 780 mV/pH corresponding to a sensing film having Nernst response. The modeling and simulation of the proposed sensor was further validated by a proof of concept extended gate pH sensor fabrication and characterization. These sensors were developed by a separated processing of just the pH sensing component, which is electrically connected to the transistor only during characterization of the sensor. This provides faster and simpler realization of the sensor without the need for masks and patterning by lithography. The extended gate sensors showed 475 mV/pH sensitivity which is superior to state of the art low power ISFETs. Finally, integration of the sensing functionality directly in the BEOL of the UTBB FDSOI devices was pursued. An experimental sensitivity of 730 mV/pH is obtained which is consistent with the mathematical model and the simulated response. This is more than 12-times higher than the Nernst limit, and superior to state of the art sensors. Sensors are also evaluated for stability, resolution, hysteresis, and drift in which excellent performances are demonstrated. A novel pH sensing architecture is also successfully demonstrated in which the detection is functionalized at the gate protection diode rather than the front gate of UTBB FDSOI devices. The abrupt current switching, as low as 9 mV/decade, has the potential to increase the fixed bias sensitivity to 6.6 decade/pH. We experimentally demonstrated a sensitivity of 1.25 decade/pH which is superior to the state of the art sensitivity

A 64×64 1200fps CMOS ion-image sensor with suppressed fixed-pattern-noise for accurate high-throughput DNA sequencing

A 64×64 CMOS ion-image sensor is demonstrated towards accurate high-throughput DNA sequencing. Dual-mode (pH/image) sensing is performed with ion-sensitive field-effect transistor (ISFET) fabricated in standard CMOS image sensor (CIS) process. After addressing physical locations of DNA slices by optical contact imaging, local pH for one DNA slice can be mapped to its physical address with accurate correlation. Moreover, pixel-to-pixel ISFET threshold voltage mismatch is reduced by correlated double sampling (CDS) readout. Measurements show a sensitivity of 103.8mV/pH and fixed-pattern-noise (FPN) reduction from 4% to 0.3% with speed of 1200fps. .Accepted versio

CMOS multimodal sensor based lab-on-a-chip system for personalized bio-imaging diagnosis

The world population is rapidly ageing with proportion of people aged 60-year-old and over, growing faster than any other age groups. Considering the current aging society, there is an emerging need to develop the future diagnosis with portable biomedical devices by bio-instrument miniaturization. The recent development of lab-on-a-chip (LOC) technology has provided a promising integration platform of microfluidic channels, microelectromechanical systems (MEMS), and sensors, which allow non-invasive and near-field sensing functions. The standard complimentary metal-oxide semiconductor (CMOS) process allows a low-cost system-on-chip solution to integrate sensors from multiple domains, which has raised many new design challenges. In this thesis, we have particularly studied the CMOS multimodal sensor for LOC integrated bio-imaging diagnosis system, including: 1) CMOS (capacitive-micromachined-ultrasonic-transducer) CMUT sensor for non-invasive ultrasound imaging towards the glaucoma diagnosis; 2) CMOS (ion-sensitive-field-effect-transistor) ISFET sensor for ion imaging towards the DNA sequencing application; and 3) CMOS optical sensor for microfluidic contact imaging towards the cell detection, recognition, and counting application. We will illustrate the need and application of the three corresponding bio-imaging diagnosis methods as well as design problems addressed when being miniaturized, which can be summarized as follows. Firstly, we illustrate one device-level design work using the example of ultrasound imaging. A two-channel analog front-end (AFE) IC for interfacing multi-channel high frequency CMUT array is developed with three-dimensional high resolution imaging capability for glaucoma diagnosis. The main challenge is the process integration between MEMS array and CMOS readout circuit, where flip-chip bonding is deployed. With the use of 30V high-voltage 0.18μm Bipolar-CMOS-DMOS (BCD) technology, the proposed AFE IC cell is designed to consist of two high-voltage (HV) pulsers in the transmit path, and a shared single low-noise pre-amplifier in the receiver path for area reduction. The electrical functionality of the proposed AFE IC is characterized in which the HV pulser generates a delay of 16.2ns between the 33ns input trigger pulse and the HV output pulse while driving the load capacitance of 43pF from 0 to 30V. And the low-noise preamplifier achieves over 60dBΩ transimpedance gain with 27.5pA/sqrt(Hz) input refereed noise current at 35MHz. A successful pulse-echo acoustic testing is also demonstrated with the developed AFE IC that integrates the CMUT sample in an oil-immersed environment. Secondly, we discuss one circuit-level design work using the example of ion imaging. A 64×64 1200fps dual-mode CMOS ion-image sensor is demonstrated with suppressed fixed-pattern-noise (FPN) for accurate high-throughput DNA sequencing. The main challenge of the traditional ISFET-based ion imaging is lack of faulty pH value detection. In this work, we show the solution by pruning sensed data with reference from multi-domain. A dual-mode ISFET sensor is developed, including pH sensing from chemical domain as well as image sensing from optical domain. An ISFET with standard 4T-CMOS image sensor (CIS) pixel structure is proposed and fabricated in standard 0.18μm 1P6M CIS process. After addressing physical locations of DNA slices determined by the optical contact imaging, local pH value of one DNA slice can be mapped to its physical address with the accurate correlation, which can significantly improve the DNA sequencing accuracy. Moreover, pixel-to-pixel ISFET threshold voltage mismatch or FPN is reduced by a correlated double sampling (CDS) readout circuit structure that supports both image and pH modes for large-array and high-throughput application. Measurement results show a sensitivity of 103.8mV/pH and FPN reduction from 4% to 0.3% with a readout speed of 1200fps. Lastly, we present one system-level design work using the example of microfluidic contact imaging. A microfluidic contact imaging system has been developed with poly-dimethylsiloxane (PDMS) microfluidic channel integrated on top of CMOS image sensor for flowing cell detection, recognition and counting. The main challenge of such a lensless microfluidic system is how to improve spatial resolution because of no optical lens. To resolve the raw spatial resolution limitation from pixel size, an extreme-learning-machine based single-frame super-resolution processing (ELM-SR) is proposed that can recover high-frequency loss in detected cell contacting images such that flowing cells can be still distinguished for counting. The prototyped lensless microfluidic system obtains less than 8% counting error for absolute number of microbeads; and 0.10 coefficient of variation for cell-ratio measurement of mixed RBC and HepG2 cells in solution. In this thesis, we have shown a thorough study to explore multimodal CMOS sensors in LOC towards the portable personalized bio-imaging diagnosis system, which could pave the way towards a variety of personalized diagnosis applications such as: 1) CMOS ultrasound sensor for non-invasive human body scanning; 2) CMOS dual-mode ion sensor for portable DNA sequencing; and 3) CMOS contact imaging sensor for point-of-care blood cell tests. Note that the primary novelty of this thesis is the design of CMOS ISFET ion-image sensor (published in IEEE Symposium on VLSI Circuits 2014). As a conclusion, the CMOS multimodal sensor based LOC system has been shown with the great potential to provide the future personalized e-healthcare solution for the coming aging society.DOCTOR OF PHILOSOPHY (EEE