Super Inkjet Printed Redistribution Layer for a MEMS Device

Printed electronics (PE) is a novel area of electronics manufacturing where functional inks and suitable ink deposition devices, such as inkjet or roll-to-roll equipment, are used to create electrically functional features. A lion’s share of current applications are in the field of low-cost, large-area electronics where the printing technologies have a significant advantage over the conventional methods due to faster processing speed and higher process flexibility. Since this has been seen as the holy grail of printed electronics, little research has been done on the field of small-area applications such as microelectronics packaging. However, with recent developments in high resolution printing, this application area should be within the reach of printing technologies as well. The main purpose of this study is to find out if the production methods developed for printed electronics could be used in the packaging of microelectromechanical systems (MEMS). Specifically, the aim is to print a high density redistribution layer (RDL) of a MEMS device package with a state of the art electrohydrodynamic (EHD) inkjet printer. By using inkjet technology instead of the current method, electrochemical plating, the costs and environmental impact of the fabrication process could be reduced significantly. This is based on the fact that inkjet printing is an additive and electrochemical plating a subtractive manufacturing method. Subtracting material leads to larger amount of wasted resources and additionally, the chemicals used to etch the copper plating are environmentally unfriendly. Additive nature of the inkjet technology increases the flexibility of production process by making the prototyping easier and enabling shorter exchange-of-die times. Applicability of EHD printing in RDL manufacturing is demonstrated by printing high density interdigital and meander structures. The secondary purpose of the thesis is to gain knowledge about operation of an EHD printer. Since this is a new development in the field of printed electronics, the existing literature is quite limited. Therefore, in addition to short literature study, statistical tools are used to look for significant parameters affecting the printing process. This analysis results in statistical models which relate the printing parameters to conductor width, thickness and sheet resistance

High-Precision Digital Printing Processes for Electronics Fabrication

This thesis investigates the capabilities of high-precision digital printing technologies in the fabrication of miniaturized components for electronics packaging, transistor intercon- nects and monolithically integrated lab-on-skin systems for biosignal monitoring. In gen- eral, the printing technologies suffer from poor resolution compared to conventional lith- ographic fabrication methods, which limits the level of miniaturization for printed elec- tronics components, devices, and circuits. This leads to their significantly lower perfor- mance compared to conventional electronics. However, certain application areas exist where pushing the envelope of printing technologies towards higher resolution and pre- cision would result in the addition of new functionalities. Replacing lithographic fabrication of high-density circuitries of electronics packages with high-resolution electrohydrodynamic inkjet (E-jet) printing could result in higher levels of customizability and reduced environmental impacts. In this thesis, the parameters affect- ing E-jet printing resolution were studied using statistical tools; the resulting regression model applied for droplet diameters of 3.5 µm to 20 µm and had a coefficient of determi- nation (R2) of 94 % with a residual of 1.1 µm. Finally, the combination of E-jet and inkjet printing is demonstrated in the fabrication of a high-density (5/5 µm width/spacing) mul- tilayer redistribution layer (RDL) for a silicon interposer. E-jet printing could be also used to enhance the interconnect density, and concomitant performance of application specific printed electronic circuits (ASPEC), which in them- selves are already an enhancement of the existing application specific integrated circuits (ASIC) in that they allow field configurability of the prefabricated logic circuits. In this thesis, E-jet printing was compared to aerosol jet (AJ), piezoelectric inkjet and litho- graphic fabrication methods for the fabrication of ASPECs. Two different interconnect structures were used and in both cases the E-jet printing compared favourably to AJ and piezoelectric inkjet printing technologies. Piezoelectric inkjet printing cannot be considered a true high-resolution technology sim- ilar to E-jet printing due to its large droplet volume (pL vs. fL), However, it may still be used to print small (i.e., high-precision) structures required for example in transistor fab- rication. The high-precision printing capability coupled with a large droplet volume ena- bles higher throughput when fabricating amplifiers with monolithically integrated active and passive components. In this thesis, a piezoelectric inkjet was used for the fabrication of source/drain (S/D) electrodes for transistors with ~10 µm channel length together with monolithically integrated large area parallel plate capacitors and resistors. The resulting charge amplifier optimized for pulse wave (PW) measurements had a gain of 1.6 V/nC with a pass band of 50 MHz to 32 Hz. Furthermore, the performance of the amplifier was evaluated for PW measurements by amplifying a PW signal recorded using piezoelectric poly(vinylidene-trifluoroethylene) (P(VDF-TrFE) pressure from the radial artery at the wrist and analyzing the amplified signal for clinically relevant PW features. As a support- ing study, the PW signal generated by a fully printed P(VDF-TrFE) pressure sensor was evaluated in a pre-clinical study with a statistically significant number of study subjects (22). Clinically relevant indices were calculated from the PW signal generated by the P(VDF-TrFE) sensor and these were compared to concurrent measurement with a ref- erence PW sensor. Good agreement between the PW sensors could be found in the case of the stiffness index (SI) and radial augmentation index (rAIx)

Effect of Electrode Structure on the Performance of Fully Printed Piezoelectric Energy Harvesters

Flexible piezoelectric energy harvesters have the potential to be used as power sources for wearable electronics. This study presents a simple printing-based fabrication process for a flexible piezoelectric energy harvesting module with an integrated and optimized SMD-based full-wave diode bridge rectifier. We investigate the effect of the electrode configuration on the energy harvesting performance of the piezoelectric elements. Two types of piezoelectric elements are fabricated (a metal-insulator-metal (MIM) structure and an interdigitated electrode (IDE) structure) for comparison. The electrodes are inkjet printed using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and the piezoelectric layer is bar coated using poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE). The results show that a higher output power density can be obtained with the MIM-based energy harvester (7.8 μW/cm3) when compared to the IDE-based harvester (20.8 nW/cm3). Simulation results show that this is explained by the higher current output (i.e., charge generation ability) of the MIM-based structure.publishedVersionPeer reviewe

A combination of experimental and numerical method for optimizing the sensitivity of ultra-thin piezoelectric sensor with interdigitated electrodes

We report the development of a finite element model (FE-model) for ultra-thin piezoelectric poly(vinylidene-trifluoroethylene) sensor with interdigitated electrodes (IDE) which includes the effect of a non-homogenous poling field determined via the combination of experimental and numerical methods. The non-homogenous poling magnitude is estimated by comparing the remanent polarization (P r) of IDE based device to the P r of the same material in metal-insulator-metal electrode configuration. The non-homogenous poling orientation is estimated by comparing the experimentally determined normal mode sensitivity (S n) values to FE-modelled sensitivity values with different poling orientation distributions. The poling orientation distribution is modelled using two approaches: (a) 33-direction parallel and perpendicular to the electrode plane and (b) 33-direction defined by an average angle. The first approach yields the best correspondence with the experimental results (R 2 = 94.70% and σ = 0.10Peer reviewe

Thermal Stability of a Fully Printed Ultra-Thin Organic Pre-Amplifier Circuit Meant for on-Skin applications

acceptedVersionPeer reviewe

Impedance plethysmography-based method in the assessment of subclinical atherosclerosis

Background and aimsThe aim of this study was to examine an association of individual and combined pulse waveform parameters derived from bioimpedance measurements, that is pulse waves from a distal impedance plethysmographic (IPG), a whole-body impedance cardiographic (ICG) and transformed distal impedance plethysmographic (tIPG) signals, with markers of subclinical atherosclerosis, i.e. carotid intima-media thickness (cIMT), brachial artery flow-mediated dilation (FMD) and carotid artery distensibility (Cdist). The level of the association was also compared for arterial pulse wave velocity (PWV) and cIMT, FMD, and Cdist.MethodsIPG, ICG, tIPG signals were measured from 1741 Finnish adults aged 30-45 years. The association between pulse wave parameters and cIMT, FMD and Cdist was studied using bootstrapped stepwise Akaike's Information Criterion method resulting in selection of parameters other than PWV, i.e. parameters having stronger association with cIMT, FMD and Cdist than PWV, in the model. Then risk scores were calculated from the selected pulse wave parameters and their association between cIMT, FMD and Cdist was studied with multivariable linear regression analysis.Results The risk score was found to be the third strongest predictor of subclinical atherosclerosis as indicated by cIMT measurement, the second strongest predictor of FMD and the strongest predictor of Cdist. These findings show that several individual pulse wave parameters were associated more strongly with cIMT, FMD, and Cdist than PWV when adjusted with clinical risk factors.ConclusionsImpedance based pulse waveform analysis provides a useful tool for assessing cardiovascular risk and estimating presence of structural changes in the vasculature.</div

Vascular adhesion protein-1 defines a unique subpopulation of human hematopoietic stem cells and regulates their proliferation

Although the development of hematopoietic stem cells (HSC) has been studied in great detail, their heterogeneity and relationships to different cell lineages remain incompletely understood. Moreover, the role of Vascular Adhesion Protein-1 in bone marrow hematopoiesis has remained unknown. Here we show that VAP-1, an adhesin and a primary amine oxidase producing hydrogen peroxide, is expressed on a subset of human HSC and bone marrow vasculature forming a hematogenic niche. Bulk and single-cell RNAseq analyses reveal that VAP-1+ HSC represent a transcriptionally unique small subset of differentiated and proliferating HSC, while VAP-1− HSC are the most primitive HSC. VAP-1 generated hydrogen peroxide acts via the p53 signaling pathway to regulate HSC proliferation. HSC expansion and differentiation into colony-forming units are enhanced by inhibition of VAP-1. Contribution of VAP-1 to HSC proliferation was confirmed with mice deficient of VAP-1, mice expressing mutated VAP-1 and using an enzyme inhibitor. In conclusion, VAP-1 expression allows the characterization and prospective isolation of a new subset of human HSC. Since VAP-1 serves as a check point-like inhibitor in HSC differentiation, the use of VAP-1 inhibitors enables the expansion of HSC.Peer reviewe

The effect of rainfall amount and timing on annual transpiration in a grazed savanna grassland

The role of precipitation (P) variability with respect to evapotranspiration (ET) and its two components, transpiration (T) and evaporation (E), from savannas continues to draw significant research interest given its relevance to a number of ecohydrological applications. Our study reports on 6 years of measured ET and estimated T and E from a grazed savanna grassland at Welgegund, South Africa. Annual P varied significantly with respect to amount (508 to 672 mm yr(-1)), with dry years characterized by infrequent early-season rainfall. T was determined using annual water-use efficiency and gross primary production estimates derived from eddy-covariance measurements of latent heat flux and net ecosystem CO2 exchange rates. The computed annual T for the 4 wet years with frequent early wet-season rainfall was nearly constant, 326 +/- 19 mm yr(-1) (T/ET=0.51), but was lower and more variable between the 2 dry years (255 and 154 mm yr(-1), respectively). Annual T and T/ET were linearly related to the early wet-season storm frequency. The constancy of annual T during wet years is explained by the moderate water stress of C4 grasses as well as trees' ability to use water from deeper layers. During extreme drought, grasses respond to water availability with a dieback-regrowth pattern, reducing leaf area and transpiration and, thus, increasing the proportion of transpiration contributed by trees. The works suggest that the early-season P distribution explains the interannual variability in T, which should be considered when managing grazing and fodder production in these grasslands.Peer reviewe

Additively fabricated on-skin sensors for mechanical and thermal biosignal monitoring

Continuous biosignal monitoring with on-skin worn sensor devices enables out-of-hospital patient monitoring (i.e. ubiquitous healthcare), which has high potential to reduce various disease-related societal costs through large-scale screening of disease risk groups. However, novel fabrication methods need to be adopted to enable the required large-scale deployment of such devices. Additive fabrication technologies have emerged as potential candidates to meet this challenge due to their low material consumption, scalability, and compatibility with skin-conformable low Tg polymeric substrates. This review article discusses recent advances in additively fabricated on-skin biosignal sensors and focuses on the following topics: (1) available additive fabrication technologies; (2) on-skin measurable mechanical and thermal biosignals and related additively fabricated biosignal sensors; and (3) the emerging field of printed electronic tattoo (e-tattoo)-type mechanical and thermal biosignal sensors.Peer reviewe

Combination of E-jet and inkjet printing for additive fabrication of multilayer high-density RDL of silicon interposer

The additive nature and high resolution of electrohydrodynamic inkjet (E-jet) printing can be utilized for manufacturing micrometer scale conductive tracks such as those required in the high-density redistribution layers (RDLs) of silicon interposers used in electronics packaging for 3-D integration. Compared to the current lithographic fabrication method, this approach promises to increase the customizability of the process and reduce the amount of waste materials, thereby lowering the costs and the environmental impact of the manufacturing process. In this paper, multilayer interdigitated capacitor and meander resistor structures with 5/5 μm conductor width/spacing are used to demonstrate the feasibility of E-jet printing of high-density multilayer RDLs. A sheet resistance of 28.5 Ω/square was achieved for the first metallization layer (MET1) conductors and 313.2 7Ω/square for the MET2 conductors. The thickness of the conductors was 6.9 μm for MET1 and 5.4 μm for MET2.acceptedVersionPeer reviewe