PLA conductive filament for 3D printed smart sensing applications

Purpose This paper aims to present a study on a commercial conductive polylactic acid (PLA) filament and its potential application in a three-dimensional (3D) printed smart cap embedding a resistive temperature sensor made of this material. The final aim of this study is to add a fundamental block to the electrical characterization of printed conductive polymers, which are promising to mimic the electrical performance of metals and semiconductors. The studied PLA filament demonstrates not only to be suitable for a simple 3D printed concept but also to show peculiar characteristics that can be exploited to fabricate freeform low-cost temperature sensors. Design/methodology/approach The first part is focused on the conductive properties of the PLA filament and its temperature dependency. After obtaining a resistance temperature characteristic of this material, the same was used to fabricate a part of a 3D printed smart cap. Findings An approach to the characterization of the 3D printed conductive polymer has been presented. The major results are related to the definition of resistance vs temperature characteristic of the material. This model was then exploited to design a temperature sensor embedded in a 3D printed smart cap. Practical implications This study demonstrates that commercial conductive PLA filaments can be suitable materials for 3D printed low-cost temperature sensors or constitutive parts of a 3D printed smart object. Originality/value The paper clearly demonstrates that a new generation of 3D printed smart objects can already be obtained using low-cost commercial materials. </jats:sec

Design and fabrication of a multipurpose compliant nanopositioning architecture

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 227-241).This research focused on generating the knowledge required to design and fabricate a high-speed application flexible, low average cost multipurpose compliant nanopositioner architecture with high performance integrated sensing. Customized nanopositioner designs can be created in ~~1 week, for 30x increase in sensing dynamic range over comparable state-of-the-art compliant nanopositioners. These improvements will remove one of the main hurdles to practical non-IC nanomanufacturing, which could enable advances in a range of fields including personalized medication, computing and data storage, and energy generation/storage through the manufacture of metamaterials. Advances were made in two avenues: flexibility and affordability. The fundamental advance in flexibility is the use of a new approach to modeling the nanopositioner and sensors as combined mechanical/electronic systems. This enabled the discovery of the operational regimes and design rules needed to maximize performance, making it possible to rapidly redesign nanopositioner architecture for varying functional requirements such as range, resolution and force. The fundamental advance to increase affordability is the invention of Non-Lithographically-Based Microfabrication (NLBM), a hybrid macro-/micro-fabrication process chain that can produce MEMS with integrated sensing in a flexible manner, at small volumes and with low per-device costs. This will allow for low-cost customizable nanopositioning architectures with integrated position sensing to be created for a range of micro-/nano- manufacturing and metrology applications. A Hexflex 6DOF nanopositioner with titanium flexures and integrated siliconpiezoresistive sensing was fabricated using NLBM. This device was designed with a metal mechanical structure in order to improve its robustness for general handling and operation. Single crystalline silicon piezoresistors were patterned from bulk silicon wafers and transferred to the mechanical structure via thin-film patterning and transfer. This work demonstrates that it is now feasible to design and create a customized positioner for each nanomanufacturing/metrology application. The Hexflex architecture can be significantly varied to adjust range, resolution, force scale, stiffness, and DOF all as needed. The NLBM process was shown to enable alignment of device components on the scale of 10's of microns. 150μm piezoresistor arm widths were demonstrated, with suggestions made for how to reach the expected lower bound of 25[mu]m. Flexures of 150[mu]m and 600[mu]m were demonstrated on 4 the mechanical structure, with a lower bound of ~~50[mu]m expected for the process. Electrical traces of 800[mu]m width were used to ensure low resistance, with a lower bound of ~~100[mu]m expected for the process. The integrated piezoresistive sensing was designed to have a gage factor of about 125, but was reduced to about 70 due to lower substrate temperatures during soldering, as predicted by design theory. The sensors were measured to have a full noise dynamic range of about 59dB over a 10kHz sensor bandwidth, limited by the Schottky barrier noise. Several simple methods are suggested for boosting the performance to ~~135dB over a 10kHz sensor bandwidth, about a <1Å resolution over the 200[mu]m range of the case study device. This sensor performance is generally in excess of presently available kHz-bandwidth analog-to-digital converters.by Robert M. Panas.Ph.D

Monolithically Integrated Diffused Silicon Two-Zone Heaters for Silicon-Pyrex Glass Microreactors for Production of Nanoparticles: Heat Exchange Aspects.

We present the design, simulation, fabrication and characterization of monolithically integrated high resistivity p-type boron-di used silicon two-zone heaters in a model high temperature microreactor intended for nanoparticle fabrication. We used a finite element method for simulations of the heaters’ operation and performance. Our experimental model reactor structure consisted of a silicon wafer anodically bonded to a Pyrex glass wafer with an isotropically etched serpentine microchannels network. We fabricated two separate spiral heaters with di erent temperatures, mutually thermally isolated by barrier apertures etched throughout the silicon wafer. The heaters were characterized by electric measurements and by infrared thermal vision. The obtained results show that our proposed procedure for the heater fabrication is robust, stable and controllable, with a decreased sensitivity to random variations of fabrication process parameters. Compared to metallic or polysilicon heaters typically integrated into microreactors, our approach o ers improved control over heater characteristics through adjustment of the Boron doping level and profile. Our microreactor is intended to produce titanium dioxide nanoparticles, but it could be also used to fabricate nanoparticles in di erent materials as well, with various parameters and geometries. Our method can be generally applied to other high-temperature microsystems

Micro-hotplate based CMOS sensor for smart gas and odour detection

Low cost, highly sensitive, miniature CMOS micro-hotplate based gas sensors have received great attention recently. The global sensor market is expanding rapidly with an expected increase of 5 ~ 8% grow thin the next five years. The application areas for a gas sensor include but are not limited to, air quality monitoring, industrial and laboratory conditions, military, and biomedical sectors. It is the key hardware component of an electronic nose, as well as the signal processing on the software side. In this thesis, both aspects of such a system were studied with new sensor technologies and improved signal processing algorithms. In addition, this thesis also described different applications and research projects using these sensor technologies and algorithms. A novel plasmonic structure was employed as an infrared source for anon- dispersive infrared gas sensor. This structure was based on a CMOS micro hot plate with three metal layers and periodic cylindrical dots to induce plasmon resonance, that allowed a tunable narrow band infrared radiation with high sensitivity and selectivity. Five gases were studied as target gases, namely, carbon monoxide, carbon dioxide, acetone, ammonia and hydrogen sulfide. These emitter sources were fabricated and characterised with a gascell, optical filters and commercial detectors under different gas concentrations and humidity levels. The results were promising with the lowest detection limit for ammonia at 10 ppm with 5 ppm resolution. On the data processing side, various signal processing methods were explored both on-board and on-board. Temperature modulation was the on-board method by switching the operating temperatures of a micro hotplate. This technique was proven to over come and reduce some typical sensor issues, such as drift, slow re-sponse/recovery speed (from tens of seconds to a few seconds) and even cross sensitivities. Off-board post processing methods were also studied, including principal component analysis, k-nearest neighbours, self-organising maps and shallow/deep neural networks. The results from these algorithms were compared and overall an 85% or higher classification accuracy could be achieved. This work showed the potential to discriminate gases/odours, which could lead to the development of a real-time discrimination algorithm for low cost wearable devices

Selective Resistive Sintering: A Novel Additive Manufacturing Process

Selective laser sintering (SLS) is one of the most popular 3D printing methods that uses a laser to pattern energy and selectively sinter powder particles to build 3D geometries. However, this printing method is plagued by slow printing speeds, high power consumption, difficulty to scale, and high overhead expense. In this research, a new 3D printing method is proposed to overcome these limitations of SLS. Instead of using a laser to pattern energy, this new method, termed selective resistive sintering (SRS), uses an array of microheaters to pattern heat for selectively sintering materials. Using microheaters offers significant power savings, significantly reduced overhead cost, and increased printing speed scalability. The objective of this thesis is to obtain a proof of concept of this new method. To achieve this objective, we first designed a microheater to operate at temperatures of 600⁰C, with a thermal response time of ~1 ms, and even heat distribution. A packaging device with electrical interconnects was also designed, fabricated, and assembled with necessary electrical components. Finally, a z-stage was designed to control the airgap between the printhead and the powder particles. The whole system was tested using two different scenarios. Simulations were also conducted to determine the feasibility of the printing method. We were able to successfully operate the fabricated microheater array at a power consumption of 1.1W providing significant power savings over lasers. Experimental proof of concept was unsuccessful due to the lack of precise control of the experimental conditions, but simulation results suggested that selectivity sintering nanoparticles with the microheater array was a viable process. Based on our current results that the microheater can be operated at ~1ms timescale to sinter powder particles, it is believed this new process can potentially be significantly quicker than selective laser sintering by increasing the number of microheater elements in the array. The low cost of a microheater array printhead will also make this new process affordable. This thesis presented a pioneering study on the feasibility of the proposed SRS process, which could potentially enable the development of a much more affordable and efficient alternative to SLS

Lift-off assisted patterning of few layers graphene

Graphene and 2D materials have been exploited in a growing number of applications and the quality of the deposited layer has been found to be a critical issue for the functionality of the developed devices. Particularly, Chemical Vapor Deposition (CVD) of high quality graphene should be preserved without defects also in the subsequent processes of transferring and patterning. In this work, a lift-off assisted patterning process of Few Layer Graphene (FLG) has been developed to obtain a significant simplification of the whole transferring method and a conformal growth on micrometre size features. The process is based on the lift-off of the catalyst seed layer prior to the FLG deposition. Starting from a SiO2 finished Silicon substrate, a photolithographic step has been carried out to define the micro patterns, then an evaporation of Pt thin film on Al2O3 adhesion layer has been performed. Subsequently, the Pt/Al2O3 lift-off step has been attained using a dimethyl sulfoxide (DMSO) bath. The FLG was grown directly on the patterned Pt seed layer by Chemical Vapor Deposition (CVD). Raman spectroscopy was applied on the patterned area in order to investigate the quality of the obtained graphene. Following the novel lift-off assisted patterning technique a minimization of the de-wetting phenomenon for temperatures up to 1000 °C was achieved and micropatterns, down to 10 µm, were easily covered with a high quality FL

A vector light sensor for 3D proximity applications: Designs, materials, and applications

In this thesis, a three-dimensional design of a vector light sensor for angular proximity detection applications is realized. 3D printed mesa pyramid designs, along with commercial photodiodes, were used as a prototype for the experimental verification of single-pixel and two-pixel systems. The operation principles, microfabrication details, and experimental verification of micro-sized mesa and CMOS-compatible inverse vector light pixels in silicon are presented, where p-n junctions are created on pyramid’s facets as photodiodes. The one-pixel system allows for angular estimations, providing spatial proximity of incident light in 2D and 3D. A two-pixel system was further demonstrated to have a wider-angle detection. Multilayered carbon nanotubes, graphene, and vanadium oxide thin films as well as carbon nanoparticles-based composites were studied along with cost effective deposition processes to incorporate these films onto 3D mesa structures. Combining such design and materials optimizations produces sensors with a unique design, simple fabrication process, and readout integrated circuits’ compatibility. Finally, an approach to utilize such sensors in smart energy system applications as solar trackers, for automated power generation optimizations, is explored. However, integration optimizations in complementary-Si PV solar modules were first required. In this multi-step approach, custom composite materials are utilized to significantly enhance the reliability in bifacial silicon PV solar modules. Thermal measurements and process optimizations in the development of imec’s novel interconnection technology in solar applications are discussed. The interconnection technology is used to improve solar modules’ performance and enhance the connectivity between modules’ cells and components. This essential precursor allows for the effective powering and consistent operations of standalone module-associated components, such as the solar tracker and Internet of Things sensing devices, typically used in remote monitoring of modules’ performance or smart energy systems. Such integrations and optimizations in the interconnection technology improve solar modules’ performance and reliability, while further reducing materials and production costs. Such advantages further promote solar (Si) PV as a continuously evolving renewable energy source that is compatible with new waves of smart city technology and systems

UV-LED Lithography system using programmable light and tilt-rotational stage for 2D/3D microfabrication for micromachined RF devices

Doctor of PhilosophyDepartment of Electrical and Computer EngineeringJungkwun KimIn this dissertation, computer-controlled multidirectional UV-LED (Ultra-Violet Light Emitting Diode) lithography has been investigated for microscale three-dimensional (3-D) fabrication processes. The scalability, changeable light intensity, and multidirectional exposure capabilities of an array of UV-LEDs as a UV light source were described and investigated for the fabrication of both conventional semiconductor devices and advanced MEMS (Micro-Electro-Mechanical-Systems) devices. The UV-LED beam is diverging in nature and fades within a short distance. Therefore, commercial collimating equipment, like Fly’s eye integrator is not suitable for the UV-LEDs. The primary contribution of this research is the development of a single lens collimation scheme for making a collimated UV-LED light source. A significant advantage of this scheme is that a high enough intensity is preserved even after collimation, facilitating millimeter-tall microfabrication. In the process of collimating the UV-LEDs individually, high contrast is observed, which is later compensated using a continuous rotation of the light source. Utilizing the independent control and the behavior of LED with the change of current and distance, additional features like regional control and adjustable intensities were added to the system. The integration of a tilt-rotational sample holder introduces the opportunity to create 3D traces of the light on the target sample, which is unique among lithography systems. In addition, the adjustable intensities remunerate the non-uniformity of the intensity caused by the inclination of the sample. The light source combines 365 nm (i-line) and 405 nm (h-line), where the i-line spectrum is targeted for several hundred-micrometer tall microfabrication, and the h-line is targeted for millimeter tall microfabrication. With the functional scalability, a large-scale (8 inch2) light source has been demonstrated with two different optical designs, one using commercial Cabochons (Pandahall) as lenses and the other with customized hexagonal lenses. The lithography system achieved collimation with a deviation of 4.13˚ with the commercial lens and a deviation of 3˚ with the hexagonal lens. An intensity of 472 mW/cm2 and 258 mW/cm2 were obtained from the H-line and I-line UV-LEDs respectively which is the highest so far. The high contrast of around 34% caused by the UV-LED matrix was minimized to around 2.5% by utilizing an orbital rotation of the LED arrays. The light source has been characterized for 8.5% uniformity. The 2D structures with a resolution of 1.4 µm and the 3D vertical structures with a height of 3.14 mm have been demonstrated using different light profiles. Complex 3D microstructures like a flat bowtie, horn, bipod, tripod, open bowtie, double arrow, three-petalled flowers, and wind vanes were fabricated utilizing the programmable multidirectional functions. A future direction of the research has been demonstrated where a self-tiltable UV-LED light source was built with an inclination range of +70˚ to -70˚. This design helps eliminate the non-uniform exposure over an inclined sample and introduces a time-efficient complex 3D microfabrication method for liquid photoresists. An array of ultra-tall microstructure fabricated using the UV-LED lithography system showed the successful application as RF frequency-selective device in the 5G frequency range. Since the RF devices are strictly responsive to their parameters, a height of around several millimeters is needed for 5G device fabrication. The high intensity of the system was able to fabricate around 2.7 mm vertical pillars resonating to 27.8 GHz. This lithography system can replace conventional UV lamps with higher and adjustable intensity ranges, larger exposure areas, multidirectional exposure, and user-friendly automatic lithography operations. In addition to tall and versatile 3D microfabrication, this system gives superior surface quality and higher production yield compared to similar technologies. With the versatile functionalities and demonstrated capabilities, this lithography tool has potential uses in bioMEMS, RF MEMS, sensors, and many other major semiconductor and MEMS applications

Valve Regulated Implantable Intrathecal Drug Deliver for Chronic Pain Management.

Chronic pain afflicts an estimated 100 million people in the United States with annual costs exceeding $100 billion. Treatment modalities for severe chronic pain include implantation of an intrathecal drug delivery device (IDDD). Conventionally, these devices are of two types: passive, permitting the delivery of a single analgesic mixture at a fixed rate; or active, permitting variable delivery by virtue of a peristaltic pump. This thesis presents an implantable system for medication delivery from multiple reservoirs with micromachined components. These components permit the use of an architecture that can provide superior volume efficiency and permit complex multi-drug delivery protocols. The system comprises three main components: regulatory valves, pressurized reservoirs, and control electronics. Important design considerations for each of these components are emphasized. Piezoelectric microvalves were designed and tested for use with aqueous flows. Two types of spring pressurized reservoirs were also designed and tested for feasibility in an IDDD. Reservoirs were pressurized using springs fabricated from silicon and generated up to 80kPa of pressure. Alternative reservoirs were pressurized using compressive metal springs and generated up to 18kPa of pressure. A first-generation system was developed that demonstrated controlled diffusion into agar gel. Water flow was regulated from 0.2-5mL/day, and bolus delivery was demonstrated. A second-generation system utilizing a two-valve manifold with embedded sensors was used to independently regulate isopropyl alcohol flow at set rates between 0.05-1mL/hr. Both systems demonstrated liquid delivery at intrathecal flow rates using continuous and duty-cycle flow regulation. Outlet pressure sensors were used to detect acute catheter occlusions and disconnects. A smart refill port was developed to allow for power transfer rates necessary to recharge batteries during a reservoir refill session. Recharging at current rates up to 500mA was demonstrated. The proposed valve-regulated architecture and two preliminary prototypes allowed evaluation of potential solutions to challenges for application of the architecture in an IDDD. Recommendations for future systems and plans for bench-top and in vitro testing are detailed. The proposed work may lead to a system that provides the functionality of commercially available implantable drug delivery devices with high volume efficiency, and the ability to independently regulate multiple medications.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75815/1/evansall_1.pd