Publication
This study adds a new dimension to lab-on-a-chip systems by employing three-dimensional (3D) integration technology for improved performance, higher functionality, and on-chip computational power. Despite the extensive amount of current research on 3D memory modules, microprocessors, and FPGAs, manufacturing and packaging challenges, as well as cost and reliability concerns have prevented the development of a 3D integrated lab-on-a-chip system. The aim of the present study was to demonstrate the feasibility of individual steps that could pave the way for the realization of smart, autonomous, low-cost, and compact biosensors for applications such as genome research, point-of-care diagnostics, drug discovery, and cell manipulation and sensing. Undoubtedly, such integration requires broad and multi-disciplinary research that combines microfabrication, biosensing, circuit design, and testing. This thesis addresses all of these aspects from manufacturing, reliability, and cost perspectives. Three major work packages are presented: (i) disposable biochip with flexible microcontacts; (ii) through-silicon-via (TSV) fabrication and chip-to-chip (C2C) integration; and (iii) microelectrode and circuit development for biosensing. Integrating the biosensing function and microfluidics on top of CMOS electronics has enabled a new generation of lab-on-a-chip systems that have addressing, sensing, and data elaboration functions on the same device. However, a key parameter for the widespread use of such system in the biosensing field is the disposability of the assay-substrate. In this context, the present study proposes a disposable biosensing layer that can be aligned and temporarily attached to the electronics through flexible interconnections and can be replaced after each measurement to eliminate the cleaning steps and cross-contamination of samples. This idea merges the advantages of passive- and active-electronic biosensors in one system and promises three key benefits: (i) high-density microelectrode array thanks to vertical interconnections; (ii) high-performance operation thanks to circuits in close proximity; and (iii) low-cost, disposable, and configurable biochips by fully decoupling the fabrication of the sensor and the electronics. The replaceable biosensing layer developed in this study is fabricated by employing four photolithography steps and by avoiding laborious and costly processes. Flexible microcontacts are realized by metal patterning and parylene deposition inside the trenches, etched on a silicon wafer by DRIE and KOH. Novel techniques are developed to pattern the frontside micro-electrode arrays and seal the wafer surface in order to prevent leakage during the measurements in liquid environment. Backside silicon DRIE is employed to form the openings for CMOS chip placement, where the alignment accuracy by manual chip placement was measured as 5 μm on average. During the preliminary tests, mechanical and electrical contact measurements we