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This paper describes the demonstration of a 4-layer wafer stack using a combination of face-to-face and back-to-back, wafer-to-wafer hybrid bonding process. Details of process flow, process characterization and challenges in multi-layer wafer stacking are included in this paper. Wafer warpage of different pattern density is simulated with 3D finite element analysis (FEA) model. Wafer bow results match with low warpage results of simulation. 4-layer wafer was stacked together without separation. The process development and improvement carries out.

Recently, there has been an increasing use of 3D stack integration for high-performance computing applications. Wafer-to-wafer (W2W) hybrid bonding is a key technology in 3D stacking integration process. However, high-density Cu-Cu hybrid bonding interconnections between W2W can give rise to structural defects, such as misalignment and delamination during the bonding process. The testing and characterization of such defects can also be difficult and challenging. This article investigates the W2W alignment accuracy of hybrid bonding process, and studies the defects in the unbonded zone around the Cu pad bonding area.

This paper presents a 3D advanced numerical modelling methodology to simulate the bonding process for fine pitch TSV wafers using wafer to wafer hybrid bonding (W2W-HB) technology from thermo-mechanical viewpoint. Two critical results affecting bonding integrity, i.e. Cu to Cu bonding area and peeling stresses on both Cu to Cu and dielectric material bonding interfaces, are investigated in details. Bonding integrity could be enhanced by reducing the peeling stresses and achieving more Cu to Cu bonding area concurrently. This paper discusses some of common design and process parameters such as dishing value, annealing temperature and dwell duration, TSV pitch and depth with regard to bonding performance. The purpose of this study is to promote a better understanding on W2W-HB so that shorter development time and better bonding integrity could be achieved.

For Wafer to Wafer Hybrid Bonding (W2W-HB) technology, warpage mitigation and precise Cu to Cu bonding are required to ensure a robust bonding integrity. This paper documents a numerical methodology using the Finite Element Analysis (FEA) tool to investigate the impact of various design and process parameters on two-layer wafer to wafer bonding. The risk of poor bonding integrity associated with inappropriate design and process parameters selected are discussed. The attempt of this paper is to promote a better understanding on the design and process parameters which could be used to establish guidelines for W2W-HB processes.

This paper reports on the comparison analysis of four main types of silicon-based microfilter for isolation of white blood cells (WBCs) from red blood cells (RBCs) in a given whole blood. The microfilter designs, namely, weir, pillar, crossflow, and membrane, all impose the same cut-off size of 3.5 mum to selectively trap WBCs. Using human whole blood, the microfilters have been characterized and compared for their blood handling capacity, WBCs trapping efficiency and RBCs passing efficiency. Based on the experimental results, the crossflow microfilter is superior and can be integrated with downstream components for on-chip genomic analysis.

A silicon microchip has been developed for purification of deoxyribonucleic acid (DNA) from human blood based on the known affinity of DNA to silica under high chaotropic salt conditions. The chip comprises several components which include a micromixer, microfilter, microbinder and two microvalves to perform the functions of the mixing, filtering, purification and fluidic control; and yet it can be accomplished by a simple mask process flow process. Original human blood sample which is a mixture of many components, including white blood cells (WBC), red blood cells (RBC), platelets, plasma, etc., can be used directly as the input sample. After cell sorting, cell lysing, DNA binding, eluting and cleaning processes, pure DNA has been extracted for the white blood cells. An average of 10 ng DNA/μl blood was able to be extracted from this fully integrated DNA extraction chip. The purity of the eluted DNA was evaluated by optical density at wavelengths of 260 nm and 280 nm. Tests results showed that the most DNA solution eluted was free from RNA and protein contamination.

Cell loss during sample transporting from macro-components to micro-components in integrated microfluidic devices can considerably deteriorate cell detection sensitivity. This intrinsic cell loss was studied and effectively minimized through (a) increasing the tubing diameter connecting the sample storage and the micro-device, (b) applying a hydrodynamic focusing approach for sample delivering to reduce cells contacting and adhesion on the walls of micro-channel and chip inlet; (c) optimizing the filter design with a zigzag arrangement of pillars (13 microm in chamber depth and 0.8 microm in gap) to prolong the effective filter length, and iv) the use of diamond shaped pillar instead of normally used rectangular shape to reduce the gap length between any two given pillar (i.e. pressure drop) at the filter region. Cell trapping and immunofluorescent detection of 12 Giardia lamblia and 12 Cryptosporidium parvum cells in 150 microl solution and 50 MCF-7 breast cancer cells in 150 microl solution was completed within 15 min with trapping efficiencies improved from 79+/-11%, 50.8+/-5.5% and 41.3+/-3.6% without hydrodynamic focusing, respectively, to 90.8+/-5.8%, 89.8+/-16.6% and 77.0+/-9.2% with hydrodynamic focusing.

This paper presents a microelectrothermofluidic packaging of integrated microdevice for viral ribonucleic acid (RNA) extraction from blood samples and its amplification through a reverse transcription (RT)-polymerase chain reaction (PCR) method for application to the point-of-care (POC) infectious disease diagnostics. Integrated microdevice consists of solid phase extraction microchannel structure, microfluidic mixer, and meander-shaped microchamber for RT-PCR. Metallic microheater and resistive temperature detection (RTD) microsenosr is monolithically integrated with fluidic components. In order to secure both electrical and fluidic interconnections, spring-loaded electrical pin and drilled microchannel structure has been design in polycarbonate micropackaging structure. In the biotesting, we have demonstrated to detect dengue serotype III virus from the 80µl of blood sample with 80pfu virus concentration.

To meet the requirements of infectious diseases identification, a sealed and fully enclosed cartridge with self-contained reagents was developed. The inlet and outlet ports of the cartridge are self-sealing. The waste produced during the diagnostic process was collected in a waste bag, which is enclosed in the cartridge. Two different types of waste bags were designed to reduce the overall thickness of the cartridge. A silicon chip with filter, binder and mixer components was integrated into the microfluidic cartridge for the extraction of the nucleic acid sample from the infectious virus sample. By using a switch valve the nucleic acid sample and waste were split and collected in a PCR tube and a waste bag respectively. The PCR tube, modified with self-sealing elastomer cap, was used for collecting the nucleic acid. The whole extraction process was carried out automatically in a small table-top actuator system. With the dengue virus as the input sample, RNA (ribonucleic acid) is extracted and subjected to RT-PCR (reverse transcription polymerase chain reaction) which detected the diagnostic size of the target amplicon.

Ultra-fine (1 microm) microfilters are required to effectively trap microbial cells. We designed microfilters featuring a rain drop bypass architecture, which significantly reduces the likelihood of clogging at the cost of limited cell loss. The new rain drop bypass architecture configuration has a substantially lower pressure drop and allows a better efficiency in trapping protozoan cells (Cryptosporidium parvum and Giardia lamblia) in comparison to our previous generation of a microfilter device. A modified version displaying sub-micron filter gaps was adapted to trap and detect bacterial cells (Escherichia coli), through a method of cells labeling, which aims to amplify the fluorescence signal emission and therefore the sensitivity of detection.

A disposable polydimethylsioxane package is developed for ‘Bio-Microfluidic System’. Disposable Bio-Microfluidic system avoids the contamination of the system after each use and this requires the use of low cost materials. Polydimethylsioxane (PDMS) is an attractive low cost material for making substrates of the micro-fluidic package. The disposable PDMS Package consists of PDMS substrates, which are fabricated by soft-lithography. The PDMS substrates are bonded together to form the disposable package with the use of a thin-film, coated both side with adhesive material. The adhesive material is selected by chemical soaking test, peel test and bio-analysis. The tests reveal that the adhesive material can handle all chemical reagents without causing blockage or discoloration to the package. The disposable PDMS package uses a plug-in concept as the macro-micro fluidic interconnects that allows easy detachment of package from the external fluidic system. The developed disposable PDMS package has demonstrated a fluidic leak-proof package that handles up to 100kPa pressure with flow-rate of 200µl/min. The package has also demonstrated that it can filter out Viral Ribonucleic Acids (RNA) from spiked blood sample. This micro fluidic package forms an integral part of the bio micro fluidic system.