IC–MEMS Co-Fabrication: Enabling smart–seamless microsystem integration for emerging biomedical technologies

The development of personalized healthcare solutions is a complex and multifaceted challenge that requires synergistic collaboration and cross-fertilization between multiple disciplines, including microelectronics, nanotechnology, materials science, and biotechnology. As numerous biomedical applications necessitate the precise regulation and observation of various biological systems at the microscale, developing integrated microsystems with functionalities that span diverse domains, such as electrical, mechanical, and optical, has become imperative in paving the way for next-generation biomedical devices. Nevertheless, as the number of microsystems within a biomedical device escalates, a pressing need emerges to interconnect these independent microsystems using an approach that meets the constraints imposed per each particular context. Wire bonding, for instance, is one of the most widely known and used methods to establish electrical connections between chips and packages. However, wire-bonded microsystems may be inadequate to fit in applications confined by the available physical space and whereby aspects such as reliability and biocompatibility are paramount. Specifically deserving attention is the increased footprint and the introduction of protrusions that may jeopardize an effective interface of biomedical devices with biological systems. Therefore, it becomes essential to devise seamless connections between these microsystems for enhanced robustness, electrical performance, compactness, and improved physical conformability to biological structures.This doctoral research was driven by the increasing demand for microsystem integration alternatives in the biomedical field and the need to develop advanced biomedical devices with improved functionality and performance. Monolithic fabrication was the principal method of establishing a seamless integration between distinct microsystems: integrated circuits—essential for the signal conditioning of transducers—and micro-electromechanical systems—excellent for implementing functionalities at the microscale via precise micromachining delicate structures on high-quality materials. Two novel biomedical devices were devised to achieve this objective: an organ-on- a-chip system for cell-culture experimentation equipped with an analog-compatible, cost-effective, BiCMOS-based temperature sensor and a stretchable polydimethyl-siloxane membrane; and an artifact-resilient optrode optimized for ultralow-noise measurements of infraslow brain activity. The latter benefited from dual-gate, low-noise, p-channel JFETs based on a BiFET technology and deep reactive ion etching on a silicon-on-insulator wafer for micromachining nonrectilinear features on the probe— essential for creating application-oriented solutions that interface better with biological structures. Both devices were designed based on a unique awareness-oriented co-design methodology that aids the device architect in undertaking design decisions of various process-related hurdles entailing co-fabrication. This methodology, namely “holistic iterative co-design thinking”, offers an iterative co-design process that facilitates the early identification of integration obstacles related to the manufacturing process. One of the key procedures in this methodology refers to functionally decomposing a multidimensional complex design problem into a set of individual one-dimensional problems that are less complex to solve. As a result, the (co)-design is iteratively readjusted, significantly saving time and resources.This dissertation also takes a new standpoint into the existing monolithic fabrication modalities, proposes a new taxonomy, clarifies terminologies, and addresses a novel co-fabrication technique: IC-interlaced-MEMS, employed for cost- effectively co-fabricating the organ-on-a-chip system described in Chapter 4. The IC-interlaced-MEMS is similar to its “sibling” IC-interleaved-MEMS. The distinction lies primarily in their degree of process orthogonality. While the IC-interleaved-MEMS benefits from fully orthogonalizing process steps between the IC and MEMS domains, the IC-interlaced-MEMS trades orthogonality for process simplification and enhanced lithographic pipeline workflow. These benefits promise to leverage the construction of next-generation biomedical devices that interact with biological systems via specialized, large-area transducers.Bio-Electronic

Design and Custom Fabrication of a Smart Temperature Sensor for an Organ-on-a-chip Platform

This paper reports on the design and fabrication of a time-mode signal-processing in situ temperature sensor customized for an organ-on-a-chip (OOC) application. The circuit was fabricated using an in-house integrated circuit (IC) technology that requires only seven lithographic steps and is compatible with MEMS fabrication process. The proposed circuit is developed to provide the first out-of-incubator temperature monitoring of cell cultures on an OOC platform in a monolithic fabrication. Measurement results on wafer reveal a temperature measurement resolution of less than ±0.2 °C (3σ) and a maximum nonlinearity error of less than 0.3% across a temperature range from 25 °C to 100 °C.Accepted author manuscriptBio-Electronic

MEMS-Electronics Integration: A Smart Temperature Sensor for an Organ-on-a-chip Platform

Bio-Electronic

Design and Custom Fabrication of a Smart Temperature Sensor for an Organ-on-a-chip Platform

Incubators in cell cultures are used to grow and maintain cells under optimal temperature alongside other key variables, such as pH, humidity, atmospheric conditions etc. As enzymatic activity and protein synthesis proceed optimally at 37.5 oC, a temperature rise can cause protein denaturation, whereas a drop in temperature can slow down catalysis and polypeptide initiation [1]. Inside the incubator, the measurements are gauged according to the temperature of the heating element, which is not exactly the same as that of the cells. Time spent outside the incubator can greatly impact cell health. In fact, out-of-incubator temperature and its change over time are unknown variables to clinicians and researchers, while a considerable number of cell culture losses are attributed to this reason. To accurately monitor the temperature of the culture throughout cell growth, an in situ temperature sensor with at least ±0.5 oC of resolution is of paramount importance. This allows the growth of the cultured cells to be optimized. This work reports on the design and fabrication of a time-mode signal-processing in situ temperature sensor customized for an organ-on-a-chip (OOC) application. The circuit was fabricated using an in-house integrated circuit technology that requires only 7 lithographic steps and is compatible with MEMS fabrication process. The proposed circuit is developed to providethe first out-of-incubator temperature monitoring of cell cultures on an OOC platform in a monolithic fabrication. Measurement results on wafer reveal a temperature measurement resolution of less than ±0.2 oC (3σ) and a maximum nonlinearity error of less than 0.3% across a temperature range from 25 oC to 100 oC. To the authors’ best knowledge, no in situ temperature-sensing fully integrated on an OOC platform exists to date. This is the first time such integration is being performed using a custom designed circuit fabricated on the same silicon substrate as that of the OOC. The simple, robust, and custom IC technology used for the sensor fabrication grants a very cost-effective integratedsolution in virtue of the reduced cost per wafer along with the large silicon area available on the platform [2]. Moreover, no further complicated assembly and subsequent protection of the prefabricated components is required. This minimizes the extra processing steps, along with the related handling risks, leading to higher yields. Finally, the freedom enjoyed by the MEMSelectronicsco-design offers a large degree of versatility to accomodate electronics in a range of different OOC shapes and structures.Bio-Electronic

Monolithic Integration of an In-situ Smart Sensor in a Silicon-based Organ-on-a-chip Platform for Monitoring the Temperature of Stem Cell Culture

This research reports on the design and co-fabrication of a time-mode signal-processing in situ temperature sensor customized for the Cytostrech, an organ-on-a-chip (OOC) device. The circuit was fabricated using an in-house integrated circuit technology (BiCMOS7) that requires only seven lithographic steps to fabricate npn and MOS devices, and is compatible with MEMS fabrication process. The technology was optimized to find the best trade-off between the the currrent gain (βF) of the BJT and the current driving capacity of the MOS devices. The proposed circuit is developed to provide the first out-of-incubator real-time temperature monitoring of cell cultures on an OOC platform in a monolithic fabrication. The importance of this temperature monitorization stems from the fact that the temperature plays a pivotal role in the cell culture. As enzymatic activity and protein synthesis proceed optimally at 37.5 °C, a temperature rise can cause protein denaturation, whereas a drop in temperature can slow down catalysis and polypeptide initiation. The temperature setpoint of the incubator is controlled according to the temperature of its sensing element, which is not always the same what the cell culture is experiencing. On the other end, the cumulative effects of time spent outside the incubator can add up and greatly impact cell health. In fact, out-of-incubator temperature and its change over time are unknown variables to clinicians and researchers, while a considerable number of cell culture losses are attributed to this reason. The system consists of two main blocks: a proportional to absolute temperature (PTAT) current generator (comprising of npn bipolar transistors to sense the temperature information) and a currentcontrolled relaxation oscillator. Measurement results on wafer reveal a temperature measurement resolution of less than ±0.2 °C (3σ) and a maximum nonlinearity error of less than 0.3% across a temperature range from 25 °C to 100 °C.Bio-Electronic

Co-integration of flip-tip patch clamp and microelectrode arrays for in-vitro recording of electrical acvity of heart cells

The patch clamp has been widely considered the gold standard to measure intracellular ionic activity of single cells [1]. However, patch clamping is a laborious method and suffers from low throughput. To mitigate the disadvantages of patch clamping, planar patch clamp (PPC) chips with higher throughput have been recently introduced [2-3]. Yet those microfluidic chips do not allow to concurrently monitor the extracellular and the intracellular activity of the cells. Understanding of the complex cellular network activity and electrochemical processes, requires correlation between local field potentials (LFPs) of a population of cells and action potentials (APs) of single cells. This abstract presents a novel CMOS compatible microfluidic system that integrates flip-tip planar patch clamps (FTPPCs) and microelectrode arrays (MEAs) on the same wafer, for invitro extra- and intra-cellular recordings of electrical activity of cardiac cells. The device is fabricated using conventional wafer front- and back-side photolithography. The fabrication process leverages anisotropic wet etching selectivity of potassium hydroxide (KOH) and deep reactive ion etching (DRIE) to pattern FTPPCs. Before DRIE process, plasma-enhanced chemical vapor deposition (PECVD) of silicon dioxide (SiO2) is applied as passivation layer. After DRIE process, a metallization step is performed by sputtering titanium nitride (TiN) on patterned structures. As the final step, SiO2 is removed and backside DRIE is used to open apertures approximately with 2 µm diameter. The FTPPCs are intended to have a tip in 20 µm depth after KOH etching, and a spacing of 200 µm to ensure that mechanical stability of the device after DRIE. The planar MEAs are then patterned on the front side with 50 µm diameter and a pitch of 200 µm. A PDMS culture chamber is attached the front-side of the wafer, while a PDMS microfluidic channel is constructed on the back-side. By applying suction through the microfluidic channels, the cells are trapped in the FTPPC apertures. Potentiostatic measurements are used to record the ionic activity of the cells intracellularly, while low-noise instrumentation amplifiers are used in combination with the MEAs, to concurrently measure LPFs. Co-integration of PPC and MEAs on the same wafer can provide valuable insight in the correlation between singBio-Electronic

Co-integration of flip-tip patch clamp and microelectrode arrays for in-vitro recording of electrical acvity of cardiac cells

Active implantable medical devices have been developed for diagnosis, monitoring and treatment of large variety of neural disorders. Since the mechanical properties of these devices need to be matched to the tissue, soft materials, such as polymers are often preferred as a substrate. 1 Parylene is a good candidate, as it is highly biocompatible and it can be deposited/etched using standard Integrated Circuit (IC) fabrication methods/processes. Further, the implantable devices should be smart, a goal that can be accomplished by including ICs. These ICs, often come in the form of additional pre-packaged components that are assembled on the implant in a heterogenous process. Such a hybrid integration, however, does not allow for size minimization, which is so critical in these applications, as otherwise the implants can cause severe damage to the tissue. On the other hand, it is essential that all components are properly packaged to prevent early failure due to moisture penetration. 2In this work we use a previously developed semi-flexible platform technology based on a Parylene substrate and Pt metallization, which allows integration of electronic components with a flexible substrate in a monolithic process. 3 We use an IC fabrication-based platform that allows for the fabrication of several rigid regions including Application-Specific Integrated Circuits (ASICs) and other components connected to each other by means of flexible interconnects. According to Fig. 1, we aim to add more functionality to this technology and thereby extend it to a platform for a variety of medical applications. An example of such functionality is integrating Light Emitting …Bio-Electronic

Design of a Multi-Functional Smart Optrode for Electrophysiology and Optogenetics

Optogenetics is a neuromodulation method that holds great potential for the realization of advanced neuroprostheses due to its precise spatial-temporal control of neuronal activity [1]. The development of novel optogenetic implants (optrodes) may open new doors to investigate complex brain circuitry and chronical brain disorders, such as epilepsy, migraine, autism, Parkinson's disease, etc [2]. Design challenges for the optrode include interference minimization between the µLED drivers and the recording electrodes, selection of proper materials, structures and dimensions to minimize tissue damage, biocompability, and batch production. In this work, we propose the construction of a multi-functional optrode to be used for physiological studies in group-housed, freely-moving rodents. It comprises commercial blue-light µLEDs for optical stimulation, an active electrode array for recording the local field potentials at different depths in the brain, and a time-domain temperature sensor. To accomplish this, silicon bulk micromachining is the essential technique used for the device manufacturation. Process steps include epitaxial growth, layers deposition, geometrical etching, ionic implantation, oxidation and diffusion. For the interconnection of the µLEDs, flip-chip bonding is used. Light intensity and frequency can be controlled via a microcontroller interface assembled on a flexible PCB mounted on the rodent head-stage. The active microelectrode array (MEA) is constructed from a Ti/TiN layer to both meet the biocompatibility requirements and to reduce the electrode-tissue interface impedance, and by this the associated thermal noise. Using a custom, simple, robust and cost-effective BiFET in-house IC technology, the recording amplifiers are monolithically integrated into the MEA to achieve a high signal-to-noise ratio (SNR) and to minimize potential crosstalk coming from the µLED drivers. Using the same BiFET IC technology, a time-domain temperature sensor is monolithically integrated into the optrode to anticipate possible brain tissue temperature changes of more than 1oC that may come from heat dissipation in the µLEDs or circuit power dissipation. Finally, the optrode is coated with a PDMS film to electrically protect the µLEDs from the tissue and avoid uncontrollable electrical stimulation of the brain tissue.Bio-ElectronicsQN/Zandbergen La

Monolithic integration of a smart temperature sensor on a modular silicon-based organ-on-a-chip device

One of the many applications of organ-on-a-chip (OOC) technology is the study of biological processes in human induced pluripotent stem cells (iPSCs) during pharmacological drug screening. It is of paramount importance to construct OOCs equipped with highly compact in situ sensors that can accurately monitor, in real time, the extracellular fluid environment and anticipate any vital physiological changes of the culture. In this paper, we report the co-fabrication of a CMOS smart sensor on the same substrate as our silicon-based OOC for real-time in situ temperature measurement of the cell culture. The proposed CMOS circuit is developed to provide the first monolithically integrated in situ smart temperature-sensing system on a micromachined silicon-based OOC device. Measurement results on wafer reveal a resolution of less than ±0.2 °C and a nonlinearity error of less than 0.05% across a temperature range from 30 to 40 °C. The sensor's time response is more than 10 times faster than the time constant of the convection-cooling mechanism found for a medium containing 0.4 ml of PBS solution. All in all, this work is the first step towards realizing OOCs with seamless integrated CMOS-based sensors capable to measure, in real time, multiple physical quantities found in cell culture experiments. It is expected that the use of commercial foundry CMOS processes may enable OOCs with very large scale of multi-sensing integration and actuation in a closed-loop system manner.Bio-ElectronicsElectronic Components, Technology and Material