HIGH PERFORMANCE PIEZOELECTRIC MATERIALS AND DEVICES FOR MULTILAYER LOW TEMPERATURE CO-FIRED CERAMIC BASED MICROFLUIDIC SYSTEMS

The incorporation of active piezoelectric elements and fluidic components into micro-electromechanical systems (MEMS) is of great interest for the development of sensors, actuators, and integrated systems used in microfluidics. Low temperature cofired ceramics (LTCC), widely used as electronic packaging materials, offer the possibility of manufacturing highly integrated microfluidic systems with complex 3-D features and various co-firable functional materials in a multilayer module. It would be desirable to integrate high performance lead zirconate titanate (PZT) based ceramics into LTCC-based MEMS using modern thick film and 3-D packaging technologies. The challenges for fabricating functional LTCC/PZT devices are: 1) formulating piezoelectric compositions which have similar sintering conditions to LTCC materials; 2) reducing elemental inter-diffusion between the LTCC package and PZT materials in co-firing process; and 3) developing active piezoelectric layers with desirable electric properties. The goal of present work was to develop low temperature fired PZT-based materials and compatible processing methods which enable integration of piezoelectric elements with LTCC materials and production of high performance integrated multilayer devices for microfluidics. First, the low temperature sintering behavior of piezoelectric ceramics in the solid solution of Pb(Zr0.53,Ti0.47)O3-Sr(K0.25, Nb0.75)O3 (PZT-SKN) with sintering aids has been investigated. 1 wt% LiBiO2 + 1 wt% CuO fluxed PZT-SKN ceramics sintered at 900oC for 1 h exhibited desirable piezoelectric and dielectric properties with a reduction of sintering temperature by 350oC. Next, the fluxed PZT-SKN tapes were successfully laminated and co-fired with LTCC materials to build the hybrid multilayer structures. HL2000/PZT-SKN multilayer ceramics co-fired at 900oC for 0.5 h exhibited the optimal properties with high field d33 piezoelectric coefficient of 356 pm/V. A potential application of the developed LTCC/PZT-SKN multilayer ceramics as a microbalance was demonstrated. The final research focus was the fabrication of an HL2000/PZT-SKN multilayer piezoelectric micropump and the characterization of pumping performance. The measured maximum flow rate and backpressure were 450 μl/min and 1.4 kPa respectively. Use of different microchannel geometries has been studied to improve the pumping performance. It is believed that the high performance multilayer piezoelectric devices implemented in this work will enable the development of highly integrated LTCC-based microfluidic systems for many future applications

Design of LTCC-based Ceramic Structure for Chemical Microreactor

The design of ceramic chemical microreactor for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. The microreactor was developed for the steam reforming of liquid fuels with water into hydrogen. The complex three-dimensional ceramic structure of the microreactor includes evaporator(s), mixer(s), reformer and combustor. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures with buried cavities and channels, and thick-film technology was used to make electrical heaters, temperature sensors and pressure sensors. The final 3D ceramic structure consists of 45 LTCC tapes. The dimensions of the structure are 75 × 41 × 9 mm3 and the weight is about 73 g

Optimization of fluidic microchannel manufacturing processes in low temperature co-fired ceramic substrates

The processing of starch powder and polymer based sacrificial layer for fabrication of microfluidic structures in low temperature co-fired ceramics (LTCC) is described in the paper. Sacrificial volume material (SVM) was placed into the channel of LTCC sheets to avoid sagging by supporting embedded, three-dimensional structures such as channels, cavities during firing. Sagging of laminated structures is a common problem in the processing of the LTCC. A series of experiments were carried out for different lamination schemes which affect the quality of LTCC sheets. Samples were tested by an acoustic microscope to reveal the internal inhomogeneities and delaminations. As a consequence of burnout, the increased fraction of evolving gases from SVM requires an adequate adaptation of the firing process to provide a residue-free burnout without damaging the structure. Using thermal analysis the intensity of the evaporating gases was determined during co-firing. Based on these results, the modification of the heating p rofile could be done. It is proposed that the fabrication of embedded structures in a multi-layer LTCC platform could be achieved by controlling SVM burnout with a modified heating profile. Using this approach, fabrication of embedded channels in LTCC substrate is demonstrated

LTCC packaging for Lab-on-a-chip application

LTCC -pakkaus Lab-on-a-chip -sovellukseen. Tiivistelmä. Tässä työssä suunniteltiin, valmistettiin ja testattiin uusi pakkaustekniikka ”Lab-on-a-chip” (LOC) -sovellukseen. Pakkaus tehtiin pii-mikrosirulle, jolla voidaan mitata solujen kiinnittymistä sirun pintaan solujen elinkelpoisuuden indikaattorina. Luotettavuustestaukset tehtiin daisy-chain -resistanssimittauksilla solunkasvatusolosuhteissa. Lisäksi työssä selvitettiin LTCC- ja ”Lab-on-a-chip” -teknologioiden perusteet teoreettiselta pohjalta. Mikrosirun pakkauksessa käytettiin joustavaa LTCC-teknologiaa. Sähköisiin kontakteihin ja niiden suojauksiin käytettiin sekä johtavia että eristäviä epoksi-liimoja. LOC-sovelluksiin on tärkeää kehittää uusia pakkausmenetelmiä jotta näiden laitteiden kaikki ominaisuudet saadaan toimimaan luotettavasti. Pakkaus testattiin samoissa olosuhteissa missä sitä tullaan käyttämään ja pakkaus kesti kaikki nämä haasteet. Lisäksi esitetty valmistusprosessi on sellainen, että sitä voidaan käyttää myös muihin ”Lab-on-a-chip” -sovelluksiin.Abstract. This work presents design, manufacturing and testing of new packaging method for Lab-on-a-chip (LOC) application. Packaging was made for silicon microchip which can measure cell adhesion on chips surface as indication of cell viability. Reliability testing was done with daisy-chain resistance measurement in real conditions. Moreover basic theory of LTCC and Lab-on-a-chip technology is presented. Resilient LTCC technology was used for packaging material and conductive/insulating epoxies were applied for electrical contacts and barriers against the environment. It is fundamentally important to develop new packaging methods for LOC applications, so all the properties can be utilized reliably. Packaging was tested under the cell growth conditions and the package showed to withstand all these challenges. Moreover the presented packaging method is possible to use also in other Lab-on-a-chip applications

Diode laser modules based on laser-machined, multi-layer ceramic substrates with integrated water cooling and micro-optics

This thesis presents a study on the use of low temperature co-fired ceramic (LTCC) material as a new platform for the packaging of multiple broad area single emitter diode lasers. This will address the recent trend in the laser industry of combining multiple laser diodes in a common package to reach the beam brightness and power required for pumping fibre lasers and for direct-diode industrial applications, such as welding, cutting, and etching. Packages based on multiple single emitters offer advantages over those derived from monolithic diode bars such as higher brightness, negligible thermal crosstalk between neighbouring emitters and protection against cascading failed emitters. In addition, insulated sub-mounted laser diodes based on telecommunication standards are preferred to diode bars and stacks because of the degree of assembly automation, and improved lifetime. At present, lasers are packaged on Cu or CuW platforms, whose high thermal conductivities allow an efficient passive cooling. However, as the number of emitters per package increases and improvements in the laser technology enable higher output power, the passive cooling will become insufficient. To overcome this problem, a LTCC platform capable of actively removing the heat generated by the lasers through impingement jet cooling was developed. It was provided with an internal water manifold capable to impinge water at 0.15 lmin-1 flow rate on the back surface of each laser with a variation of less than 2 °C in the temperature between the diodes. The thermal impedance of 2.7°C/W obtained allows the LTCC structure to cool the latest commercial broad area single emitter diode lasers which deliver up to 13 W of optical power. Commonly, the emitters are placed in a “staircase” formation to stack the emitters in the fast-axis, maintaining the brightness of the diode lasers. However, due to technical difficulties of machining the LTCC structure with a staircase-shaped face, a novel out-plane beam shaping method was proposed to obtain an elegant and compact free space combination of the laser beam on board using inexpensive optics. A compact arrangement was obtained using aligned folding mirrors, which stacked the beams on top of each other in the fast direction with the minimum dead space

Hybridization of additive manufacturing processes for fabrication of functional ceramics with embedded microchannels

This thesis presents the results of a work concerning a novel technology based on the combination of two different additive manufacturing techniques applied to ceramics materials, namely Layerwise slurry deposition and Robocasting, aimed to obtain functional ceramics with embedded microchannel

Electrochemical Immunosensing of Cortisol in an Automated Microfluidic System Towards Point-of-Care Applications

This dissertation describes the development of a label-free, electrochemical immunosensing platform integrated into a low-cost microfluidic system for the sensitive, selective and accurate detection of cortisol, a steroid hormone co-related with many physiological disorders. Abnormal levels of cortisol is indicative of conditions such as Cushing’s syndrome, Addison’s disease, adrenal insufficiencies and more recently post-traumatic stress disorder (PTSD). Electrochemical detection of immuno-complex formation is utilized for the sensitive detection of Cortisol using Anti-Cortisol antibodies immobilized on sensing electrodes. Electrochemical detection techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) have been utilized for the characterization and sensing of the label-free detection of Cortisol. The utilization of nanomaterial’s as the immobilizing matrix for Anti-cortisol antibodies that leads to improved sensor response has been explored. A hybrid nano-composite of Polyanaline-Ag/AgO film has been fabricated onto Au substrate using electrophoretic deposition for the preparation of electrochemical immunosening of cortisol. Using a conventional 3-electrode electrochemical cell, a linear sensing range of 1pM to 1µM at a sensitivity of 66µA/M and detection limit of 0.64pg/mL has been demonstrated for detection of cortisol. Alternately, a self-assembled monolayer (SAM) of dithiobis(succinimidylpropionte) (DTSP) has been fabricated for the modification of sensing electrode to immobilize with Anti-Cortisol antibodies. To increase the sensitivity at lower detection limit and to develop a point-of-care sensing platform, the DTSP-SAM has been fabricated on micromachined interdigitated microelectrodes (µIDE). Detection of cortisol is demonstrated at a sensitivity of 20.7µA/M and detection limit of 10pg/mL for a linear sensing range of 10pM to 200nM using the µIDE’s. A simple, low-cost microfluidic system is designed using low-temperature co-fired ceramics (LTCC) technology for the integration of the electrochemical cortisol immunosensor and automation of the immunoassay. For the first time, the non-specific adsorption of analyte on LTCC has been characterized for microfluidic applications. The design, fabrication technique and fluidic characterization of the immunoassay are presented. The DTSP-SAM based electrochemical immunosensor on µIDE is integrated into the LTCC microfluidic system and cortisol detection is achieved in the microfluidic system in a fully automated assay. The fully automated microfluidic immunosensor hold great promise for accurate, sensitive detection of cortisol in point-of-care applications

Fabrication and Characterization of Miniaturized Components Based on Extruded Ceramic-Filled Polymer Blends

The objective of this work is to develop an improved manufacturing process for microstructured ceramic components that is based on co-extrusion. Co-extrusion of structured feedrods holds promise for development of multi-layered, functionally graded and/or textured structures. However, it requires a polymer binder that is difficult to remove before structures can be sintered to full density. A two-step debinding is introduced to eliminate debinding defects that are commonly observed in thermal debinding (TD). Cracking is a major issue due to a lack of pore spaces for outgassing of pyrolysis products in traditional TD. In two-step debinding, a soluble binder is removed partially by solvent extraction (SE) which creates a porous network and allows gases to escape in subsequent TD of remaining binder components. The feasibility of solvent extraction (SE) is documented for the extrusion of solid ceramic rods and co-extrusion of tubes, where alumina powder was batched with polyethylene butyl acrylate (PEBA) as backbone polymer and polyethylene glycol (PEG) as water soluble binder. SE for specimens with varying PEBA:PEG ratios were tested in water at three different temperatures for various times. Experiments were also performed with different grades of PEBA and EVA to investigate the effect of thermoplastics on SE. The 1:1 mixture showed a PEG removal up to 80wt.% of the original PEG content after 6h extraction. After subsequent thermal debinding, rods and tubes were sintered successfully without defects, demonstrating the viability of the process. Scanning electron microscopy and optical analysis were performed to characterize the process. In order to illustrate potential applications, microfluidic devices were manufactured using extrusion followed by hot embossing. Ceramic microfabricated components have advantages over silicon, glass or polymer devices in terms of their ability to sustain high temperatures without compromising their functional capabilities. Flat tapes were extruded to create substrates, which were subsequently embossing micro patterns using a brass metal mold. To seal the microchanneled feature, a glass slide was attached to the chip by thermal bonding. Though a good bond was obtained, small portions were found where poor bonding was observed. To check leakage, colored water was forced to flow through the channel,and no leakage of water was found. A low temperature sintered ceramic material was fabricated as a potential alternative to the commercial low temperature co-fired ceramic (LTCC) tape. Overall, the study describes new possibilities for microstructure fabrication on ceramic based substrate and established the embossing process as a promising technique for fabrication