publications | Katherine Song

2026

CHI

Entangled Life and Code: A Computational Design Taxonomy for Synergistic Bio-Digital Systems

Zoë Breed, Elvin Karana, Alessandro Bozzon, and Katherine W Song

In Proceedings of the 2026 CHI Conference on Human Factors in Computing Systems, 2026

Abstract PDF

Bio-digital systems that merge microbial life with technology promise new modes of computation, combining biological adaptability with digital precision. Yet realizing this potential symbiotically – where biological and digital agents co-adapt and co-process – remains elusive, largely due to the absence of a shared vocabulary bridging biology and computing. Consequently, microbes are often constrained to uni-directional roles, functioning as sensors or actuators rather than as active, computational partners in bio-digital systems. In response, we propose a taxonomy and pathways that articulate and expand the roles of biological and digital entities for synergetic bio-digital computation. Using this taxonomy, we analysed 70 systems across HCI, design, and engineering, identifying how biological mechanisms can be mapped onto computational abstractions. We argue that such mappings enable computationally actionable directions that foster richer and reciprocal relationships in bio-digital systems, supporting regenerative ecologies across time and scale while inspiring new paradigms for computation in HCI.
Growing Bio-HCI at CHI: Exchanging Materials, Tools, Practices, and Artifacts

Fiona Bell, Jingwen Zhu, Nadia Campo Woytuk, Fernanda Costa, Lauren Thu, Qiuyu Lu, Katherine W Song, Phillip Gough, Cindy Hsin-Liu Kao, Marion Koelle, Valentina Nisi, and Ron Wakkary

In Proceedings of the Extended Abstracts of the 2026 CHI Conference on Human Factors in Computing Systems, 2026

Abstract

Biological Human-Computer Interaction (Bio-HCI) has recently emerged as a rapidly growing and evolving area of research that explores the intersections of biology and technology. While vast in scope, the integration of biological systems, processes, and organisms within HCI serves as fertile ground for developing new, sustainable perspectives and methods of design. Consequently, this workshop aims to grow the ecosystem of Bio-HCI works by facilitating a space for experienced researchers and practitioners to exchange biomaterial recipes, biofabrication tools, biomaking practices, and biodesigned artifacts. Participants will share these contributions in a show-and-tell format—providing physical samples to demonstrate and explain their work. The show-and-tell will further provide a scaffold for drawing connections between works and serve as a starting point to discuss challenges, tensions, and barriers, followed by future opportunities. All show-and-tell contributions will be compiled into a collective zine to highlight, disseminate, and cultivate the current ecosystem of Bio-HCI at CHI.

2025

Wearable Bio-HCI: Challenges & Opportunities

Jingwen Zhu, Fiona Bell, Katherine W Song, Katia Vega, Aditya Shekhar Nittala, Mirela Alistar, Leah Buechley, and Cindy Hsin-Liu Kao

In Proceedings of the Extended Abstracts of the CHI Conference on Human Factors in Computing Systems, 2025

Abstract PDF

Biological Human-Computer Interaction (Bio-HCI) investigates the dynamic relationship between humans, computers, and biological systems. There has been a growing interest in integrating biological components into wearable human-computer interactions to expand their functional capabilities, material options, and design processes. Researchers have explored novel systems such as biofluid sensing for personal health, sustainable fabrication practices using biomaterials for creating wearables, and integrating living matter into wearable forms. However, as a rapidly growing, multidisciplinary field, Wearable Bio-HCI faces unique challenges and opportunities that demand collective efforts from a diverse group of researchers and practitioners. In this special interest group, we aim to gather researchers who are in this field or interested in integrating Bio-HCI approaches for creating novel interactive wearables. Our goal is to identify, brainstorm, and discuss challenges and opportunities that are unique to wearable Bio-HCI explorations. We aim to generate ideas on community engagement and cross-disciplinary collaboration for future research.
TOCHI

Unmaking & HCI: Techniques, Technologies, Materials, and Philosophies Beyond Making

Katherine W. Song, Samar Sabie, Steven Jackson, Kristina Lindström, Eric Paulos, Åsa Ståhl, and Ron Wakkary

ACM Trans. Comput.-Hum. Interact., Jan 2025

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2024

CHI

Füpop: "Real Food" Flavor Delivery via Focused Ultrasound

Katherine W. Song, Szu Ting Tung, Alexis Kim, and Eric Paulos

In Proceedings of the CHI Conference on Human Factors in Computing Systems, Jan 2024

Abstract PDF

Food and flavors are integral to our existence in the world. Nonetheless, taste remains an under-explored sense in interaction design. We present Füpop, a technical platform for delivering in-mouth flavors that leverages advances in electronics and molecular gastronomy. Füpop comprises a fully edible pouch placed inside the mouth against a cheek that programmatically releases different flavors when wirelessly triggered by a focused ultrasound transducer from outside the cheek. Füpop does not interfere with activities such as chewing and drinking, and its electronics may be integrated into devices already used near the cheek, such as mobile phones, audio headphones, and head-mounted displays. Füpop’s flavors are from "real foods,"" not ones imitated with synthetic reagents, providing authentic, nutritive flavors. We envision that with Füpop, flavors may be synced to music, a phone call, or events in virtual reality to enhance a user’s experience of their food and the world.
CHI

Sustainable Unmaking: Designing for Biodegradation, Decay, and Disassembly

Katherine W. Song, Fiona Bell, Himani Deshpande, Ilan Mandel, Tiffany Wun, Mirela Alistar, Leah Buechley, Wendy Ju, Jeeeun Kim, Eric Paulos, Samar Sabie, and Ron Wakkary

In CHI Conference on Human Factors in Computing Systems Extended Abstracts (Workshop), Jan 2024

Abstract PDF

Unmaking is a counterpart to making and creating new things that has emerged as a concept of interest in diverse parts of the HCI community. Unmaking has been posed as an ally to sustainability, encouraging designers to foreground issues relating to reuse, repair, obsolescence, degradation, and decay early in their design process. As a follow-up to the 2022 Unmaking@CHI workshop, this workshop will bring together researchers and practitioners interested in unmaking as it relates to sustainability and will focus primarily on exploring the role of unmaking in material practices, drawing upon the growing body of unmaking theory to explore future research opportunities for designing physical things with sustainable materials that are transient, degradable, and intentionally unmake-able. In addition to considering the pragmatics of what and how to unmake, we seek to articulate the relationships among unmaking and other related emerging themes and sustainable material practices – including biodegradation, designing with more-than-human agencies, reuse, and repair – and propose guidelines for designing for the unmaking of physical artifacts that are sustainable, equitable, and respectful of all entities involved.

2023

UIST

Decomposable Interactive Systems

Katherine W. Song

In Adjunct Proceedings of the 36th Annual ACM Symposium on User Interface Software and Technology, Jan 2023

Abstract PDF

As sustainability becomes an increasingly pressing concern across disciplines, the design and fabrication communities within HCI are rapidly discovering and sharing a wealth of novel materials, tools, and workflows, allowing us to make physical artifacts that are more eco-friendly than ever before. Still, sustainability and functionality are often at odds with one another when it comes to the design of interactive systems, with most systems still relying on conventional electronic components that must be extracted and individually handled at end of life. My work offers approaches for designing decomposable interactive systems that are made with materials that are widely available, safe, and even edible, empowering the “everyday designer” to make sustainable systems for applications that do not demand long operation times or high power. Enabled by the growing ecosystem of decomposable materials and systems, I also propose new opportunities for designing for unmaking, a counterpart to making that opens the opaque, industrial processes of recycling and composting as rich design spaces to encourage further engagement and critical reflection around themes of sustainability, materiality, and consumption.
CHI

Lotio: Lotion-Mediated Interaction with an Electronic Skin-Worn Display

Katherine W. Song*, Christine Dierk*, Szu Ting Tung, and Eric Paulos

In Proceedings of the 2023 CHI Conference on Human Factors in Computing Systems, Jan 2023

Abstract PDF

Skin-based electronics are an emerging genre of interactive technologies. In this paper, we leverage the natural uses of lotions and propose them as mediators for driving novel, low-power, quasi-bistable, and bio-degradable electrochromic displays on the skin and other surfaces. We detail the design, fabrication, and evaluation of one such “Lotion Interface,” including how it can be customized using low-cost everyday materials and technologies to trigger various visual and temporal effects – some lasting up to fifteen minutes when unpowered. We characterize different fabrication techniques and lotions to demonstrate various visual effects on a variety of skin types and tones. We highlight the safety of our design for humans and the environment. Finally, we report findings from an exploratory user study and present a range of compelling applications for Lotion Interfaces that expand the on-skin and surface interaction landscapes to include the familiar and often habitual practice of applying lotion.
CHI

Vim: Customizable, Decomposable Electrical Energy Storage

Katherine W. Song and Eric Paulos

In Proceedings of the 2023 CHI Conference on Human Factors in Computing Systems, Jan 2023

Abstract PDF

Providing electrical power is essential for nearly all interactive technologies, yet it often remains an afterthought. Some designs handwave power altogether as an “exercise for later.” Others hastily string together batteries to meet the system’s electrical requirements, enclosing them in whatever box fits. Vim is a new approach – it elevates power as a first-class design element; it frees power from being a series of discrete elements, instead catering to exact requirements; it enables power to take on new, flexible forms; it is fabricated using low-cost, accessible materials and technologies; finally, it advances sustainability by being rechargeable, non-toxic, edible, and compostable. Vims are decomposable battery alternatives that rapidly charge and can power small applications for hours. We present Vims, detail their characteristics, offer design guidelines for their fabrication, and explore their use in applications spanning prototyping, fashion, and food, including novel systems that are entirely decomposable and edible.
Biodegradable packaging with integrated heating system

Aditi Maheshwari, Katherine Wei Song, and Eric Michael Gallo

US Patent App 17/505,705, Feb 2023

2022

CHI

Towards Decomposable Interactive Systems: Design of a Backyard-Degradable Wireless Heating Interface

Katherine W. Song, Aditi Maheshwari, Eric M. Gallo, Andreea Danielescu, and Eric Paulos

In Proceedings of the 2022 CHI Conference on Human Factors in Computing Systems, Feb 2022

🏅 Best Paper Honorable Mention (top 5%)
Abstract PDF

Sustainability is critical to our planet and thus our designs. Within HCI, there is a tension between the desire to create interactive electronic systems and sustainability. In this paper, we present the design of an interactive system comprising components that are entirely decomposable. We leverage the inherent material properties of natural materials, such as paper, leaf skeletons, and chitosan, along with silver nanowires to create a new system capable of being electrically controlled as a portable heater. This new decomposable system, capable of wirelessly heating to >70°C, is flexible, lightweight, low-cost, and reusable, and it maintains its functionality over long periods of heating and multiple power cycles. We detail its design and present a series of use cases, from enabling a novel resealable packaging system to acting as a catalyst for shape-changing designs and beyond. Finally, we highlight the important decomposable property of the interactive system when it meets end-of-life.
CHI

Unmaking@CHI: Concretizing the Material and Epistemological Practices of Unmaking in HCI

Samar Sabie, Katherine W. Song, Tapan Parikh, Steven J. Jackson, Eric Paulos, Kristina Lindström, Åsa Ståhl, Dina Sabie, Kristina Andersen, and Ron Wakkary

In CHI Conference on Human Factors in Computing Systems Extended Abstracts (Workshop), Feb 2022

Abstract PDF

Design is conventionally considered to be about making and creating new things. But what about the converse of that process – unmaking that which already exists? Researchers and designers have recently started to explore the concept of “unmaking” to actively think about important design issues like reuse, repair, and unintended socio-ecological impacts. They have also observed the importance of unmaking as a ubiquitous process in the world, and its relation to making in an ongoing dialectic that continually recreates our material and technological realms. Despite the increasing attention to unmaking, it remains largely under-investigated and under-theorized in HCI. The objectives of this workshop are therefore to (a) bring together a community of researchers and practitioners who are interested in exploring or showcasing the affordances of unmaking, (b) articulate the material and epistemological scopes of unmaking within HCI, and (c) reflect on frameworks, research approaches, and technical infrastructure for unmaking in HCI that can support its wider application in the field.

2021

CHI

Unmaking: Enabling and Celebrating the Creative Material of Failure, Destruction, Decay, and Deformation

Katherine W. Song and Eric Paulos

In Proceedings of the 2021 CHI Conference on Human Factors in Computing Systems, Feb 2021

Abstract PDF

The access and growing ubiquity of digital fabrication has ushered in a celebration of creativity and "making." However, the focus is often on the resulting static artifact or the creative process and tools to design it. We envision a post-making process that extends past these final static objects – not just in their making but in their “unmaking.” By drawing from artistic movements such as Auto-Destructive Art, intentionally inverting well-established engineering principles of structurally sound designs, and safely misusing unstable materials, we demonstrate an important extension to making – unmaking. In this paper, we provide designers with a new vocabulary of unmaking operations within standard 3D modeling tools. We demonstrate how such designs can be realized using a novel multi-material 3D printing process. Finally, we detail how unmaking allows designs to change over time, is an ally to sustainability and re-usability, and captures themes of "aura," emotionality, and personalization.
CHI

Crank That Feed: A Physical Intervention for Active Twitter Users

Katherine W. Song*, Janaki Vivrekar*, Lynn Yeom*, Eric Paulos, and Niloufar Salehi

In CHI Conference on Human Factors in Computing Systems Extended Abstracts, Feb 2021

Abstract PDF

Passively consuming digital social media content often precludes users from mindfully considering the value they derive from such experiences as they engage in them. We present a system for using Twitter that requires users to continuously turn a hand crank to power their social media screen. We evaluate the device and its effects on how users value Twitter with 3 participants over 3 weeks, with the middle week of Twitter usage directed exclusively through our system. Using our device caused a dramatic decrease in Twitter usage for all participants, which either persisted or rebounded in the post-intervention week. Our analysis of diary studies and qualitative interviews surfaced three themes indicating shifting focus on content, shifting awareness about the role of social media, and new social dynamics around content-sharing.

2020

Adaptive Pixel Uniformity Compensation for Display Panels

Shengkui Gao, Hung Sheng Lin, Hyunsoo Kim, Hyunwoo Nho, Katherine W. Song, Mohammad Hajirostam, Myung-Je Cho, Rui Zhang, Sang Y. Youn, Wei H. Yao, and Yafei Bi

US Patent US 10,529,053 B2, Jan 2020

Abstract PDF

A display device may include a display having a pixels and a processor. The processor may receive image data, determine a digital offset value for a pixel based on a location of the pixel, such that the digital offset value compensates for one or more non-uniformity properties of the pixel. The processor may determine a scale factor associated with the pixel based on at least two of a luminance setting for the display, a driving mode of the display, and a gray level value for the pixel. The processor may then generate correction image data by applying the scale factor to the digital offset value, generate compensated image data based on the correction image data and the image data, and provide the compensated image data to the display.

2018

Near-Infrared Light Emitting Device using Semiconductor Nanocrystals

Geoffrey J. S. Supran, Katherine W. Song, Gyuweon Hwang, Raoul Emile Correa, Yasuhiro Shirasaki, Moungi G. Bawendi, Vladimir Bulovic, and Jennifer Scherer

US Patent US 9,935,240 B2, Apr 2018

Abstract PDF

A near-infrared light emitting device can include semiconductor nanocrystals that emit at wavelengths beyond 1 μm. The semiconductor nanocrystals can include a core and an overcoating on a surface of the core.

2016

Assessment of Nerve Regeneration through a Novel Microchannel Array

Benjamin Maimon, Anthony N. Zorzos, Katherine Song, Rhyse Bendell, Ron Riso, and Hugh Herr

International Journal of Physical Medicine & Rehabilitation, Apr 2016

Abstract PDF

Advancements in robotic technologies have enabled a significant improvement in the clinical efficacy of prosthetic limbs for persons with upper and lower-extremity amputations. However, significant challenges still remain in establishing a biomimetic bidirectional neural communication between amputees and their external powered prostheses. Regenerative peripheral nerve interfaces may offer a high-resolution alternative to conventional nerve interface technologies for their unique potential to provide increased biospatial resolution for both the control of and feedback from an external powered prosthesis. Here, we present three separate design for 3-D microchannel arrays, each having 16-20 channels measuring 200 μm by 200 μm: one passive (without integrated electrodes), one active (with integrated electrodes), and one active with a porous collagen scaffold. With the array positioned between proximal and distal nerve sendings, we evaluate their effectiveness in tibial n. regeneration in vivo in both rats (N=4) and ferrets (N=4). Using immunofluorescence, we report robust mixed sensory and motor nerve regeneration through the microchannels in all rats, and weak regeneration in 2 of 4 ferrets, suggesting both interspecies regeneration variability and the lack of benefit of axially oriented collagen in improving ferret nerve regeneration through microchannels.
Deposition of Semiconductor Nanocrystals for Light Emitting Devices

Vladimir Bulović, Katherine Wei Song, and Ronny Costi

US Patent US 9,472,723 B2, Oct 2016

Abstract PDF

A method of depositing semiconductor nanocrystals on a surface can include applying a voltage to the nanocrystals.
Peripheral Neural Interface via Nerve Regeneration to Distal Tissues

Hugh M. Herr, Ronald R. Riso, Katherine W. Song, Richard J. Casler, and Matthew J. Carty

US Patent US 9,474,634 B2, Oct 2016

Abstract PDF

At least partial function of a human limb is restored by surgically removing at least a portion of an injured or diseased human limb from a surgical site of an individual and transplanting a selected muscle into the remaining biological body of the individual, followed by contacting the transplanted selected muscle, or an associated nerve, with an electrode, to thereby control a device, such as a prosthetic limb, linked to the electrode. Simulating proprioceptive sensory feedback from a device includes mechanically linking at least one pair of agonist and antagonist muscles, wherein a nerve innervates each muscle, and supporting each pair with a support, whereby contraction of the agonist muscle of each pair will cause extension of the paired antagonist muscle. An electrode is implanted in a muscle of each pair and electrically connected to a motor controller of the device, thereby simulating proprioceptive sensory feedback from the device.

2015

Adv Mater

High-Performance Shortwave-Infrared Light-Emitting Devices Using Core-Shell (PbS-CdS) Colloidal Quantum Dots

Geoffrey J. Supran, Katherine W. Song, Gyu Weon Hwang, Raoul E. Correa, Jennifer Scherer, Eric A. Dauler, Yasuhiro Shirasaki, Moungi G. Bawendi, and Vladimir Bulović

Advanced Materials, Feb 2015

Abstract PDF

Core–shell PbS–CdS quantum dots enhance the peak external quantum efficiency of shortwave‐infrared light‐emitting devices by up to 50–100‐fold (compared with core‐only PbS devices). This is more than double the efficiency of previous quantum‐dot light‐emitting devices operating at wavelengths beyond 1 μm, and results from the passivation of the PbS cores by the CdS shells against in situ photoluminescence quenching.

2013

Fabrication and Optimization of Light Emitting Devices with Core-Shell Quantum Dots

Katherine Wei Song

Master's Thesis (MIT), Feb 2013

Abstract PDF

Quantum dot light emitting devices (QD-LEDs) are promising options for the next generation of solid state lighting, color displays, and other optoelectronic applications. Overcoating quantum dots (QDs) – semiconducting nanocrystals of CdSe, PbS, or another similar compound – with a wide band-gap "shell" has recently been shown to significantly boost QD-LED performance and yield the most efficient QD-LEDs to date. This thesis studies fabrication techniques to make bright, efficient QD-LEDs with these "core-shell" QDs. The first part studies the electrophoretic deposition (EPD) of CdSe/ZnS QDs. QD-LEDs conventionally utilize a QD film that is deposited via spin-casting, a reliable but highly unscalable technique for the deposition of thin, smooth films of QDs for QD-LED applications. Potential advantages of EPD include the ability for deposition onto a variety of substrate shapes and more energetically favorable QD packing. Devices made with EPD QD films exhibit peak efficiencies comparable to those of devices with a spun-cast QD layer and turn-on voltages surprisingly lower than the optical band-gap of the QDs. These results suggest that EPD is a viable alternative to spin-casting for the processing of QD-LEDs. The second part of this thesis explores the role of core-shell QDs in creating bright, efficient LEDs in the near-infrared (λ > 1 µm) regime. Infrared QD-LEDs with record brightness and efficiencies are obtained by using QDs in which lead sulfide (PbS) cores are overcoated with a cadmium sulfide (CdS) shell. In situ photoluminescence quantum yield measurements confirm that the QD shell plays a significant role in shielding the emissive QD core from external quenching mechanisms.
MRS Bull

QLEDs for displays and solid-state lighting

Geoffrey J. Supran, Yasuhiro Shirasaki, Katherine W. Song, Jean-Michel Caruge, Peter T. Kazlas, Seth Coe-Sullivan, Trisha L. Andrew, Moungi G. Bawendi, and Vladimir Bulović

MRS Bulletin, Sep 2013

Abstract PDF

The mainstream commercialization of colloidal quantum dots (QDs) for light-emitting applications has begun: Sony televisions emitting QD-enhanced colors are now on sale. The bright and uniquely size-tunable colors of solution-processable semiconducting QDs highlight the potential of electroluminescent QD light-emitting devices (QLEDs) for use in energy-efficient, high-color-quality thin-film display and solid-state lighting applications. Indeed, this year’s report of record-efficiency electrically driven QLEDs rivaling the most efficient molecular organic LEDs, together with the emergence of full-color QLED displays, foreshadow QD technologies that will transcend the optically excited QD-enhanced products already available. In this article, we discuss the key advantages of using QDs as luminophores in LEDs and outline the 19-year evolution of four types of QLEDs that have seen efficiencies rise from less than 0.01% to 18%. With an emphasis on the latest advances, we identify the key scientific and technological challenges facing the commercialization of QLEDs. A quantitative analysis, based on published small-scale synthetic procedures, allows us to estimate the material costs of QDs typical in light-emitting applications when produced in large quantities and to assess their commercial viability.
Adv Mater

Electrophoretic Deposition of CdSe/ZnS Quantum Dots for Light-Emitting Devices

Katherine W. Song, Ronny Costi, and Vladimir Bulović

Advanced Materials, Mar 2013

Abstract PDF

The electrophoretic deposition of thin films of colloidal quantum dots is an alternative to spin-casting and printing for large-area, high-throughput processing of quantum-dot (QD) optoelectronics. In this study, QD light-emitting diodes (QD-LEDs) fabricated with electrophoretically deposited films of CdSe/ZnS core/shell QDs are demonstrated for the first time.

2012

VLSIC

High-resolution sensing sheet for structural-health monitoring via scalable interfacing of flexible electronics with high-performance ICs

Yingzhe Hu, Warren Rieutort-Louis, Josue Sanz-Robinson, Katherine Song, James C. Sturm, Sigurd Wagner, and Naveen Verma

In 2012 Symposium on VLSI Circuits (VLSIC), Jun 2012

Abstract PDF

Early-stage damage detection for buildings and bridges re quires continuously sensing and assessing strain over large sur faces, yet with centimeter-scale resolution. To achieve this, we present a sensing sheet that combines high-performance ICs with flexible electronics, allowing bonding to such surfaces. The flexi ble electronics integrates thin-film strain gauges and amorphous silicon control circuits, patterned on a polyimide sheet that can potentially span large areas. Non-contact links couple digital and analog signals to the ICs, allowing many ICs to be intro duced via low-cost sheet lamination for energy-efficient readout and computation over a large number of sensors. Communi cation between distributed ICs is achieved by transceivers that exploit low-loss interconnects patterned on the polyimide sheet; the transceivers self-calibrate to the interconnect impedance to maximize transmit SNR. The system achieves multi-channel strain readout with sensitivity of 18J1’strainRMs at an energy per measurement of 270nJ, while the communication energy is 12.8pJ/3.3pJ per bit (Tx/Rx) over 7.5m.

2011

Measurements of the localized state electronic structure of organic solar cells

R. A. Street and K. W Song

In 2011 37th IEEE Photovoltaic Specialists Conference, Jun 2011

Abstract PDF

Experimental measurements of the band tail density of states distribution in bulk heterojunction solar cells, are described, with measurements made on P3HT:PCBM and PCDTBT:PCBM. The transient photoconductivity experiment measures the electron and hole drift mobility in the solar cells. The dispersive nature of the electronic transport is directly related to the band tail density of states distribution. The technique is extended to measure the band tail DOS over a range of energies. In each type of cell we observe an approximately exponential band tail, but also find an additional broad distribution of deep states. Measurements of the photocurrent spectral response to low energy provide an alternative measure of the optical absorption spectrum for excitations from the polymer HOMO to the PCBM LUMO. These data also reveal an exponential distribution of band tail states with a slope that is the same as the electron transport measurements.
The homemaker’s hydrogen generator: A report for IAHE student hydrogen design competition 2010

Yin Liang, Katherine Song, Leo Shaw, Michael Zhu, Alex Tait, Nicole Businelli, Jane Yang, Ryan Soussan, Haonan Zhou, Jimmy Lu, and Thomas Mbise

International Journal of Hydrogen Energy, Oct 2011

Abstract PDF

As a highly reactive gas, hydrogen presents significant challenges for its acquisition and safe storage. Consequently, the viability of a sustainable hydrogen economy greatly depends on the development of an efficient, cost-effective method of hydrogen production. One model for addressing this challenge is to deploy portable hydrogen generators for the home. The Princeton University Chapter of the International Association for Hydrogen Energy (IAHE-PU) has designed and created a generator that produces hydrogen through water electrolysis and optimizes cost effectiveness and portability while maximizing hydrogen output.
Org Electron

Influence of series resistance on the photocurrent analysis of organic solar cells

R.A. Street, K.W. Song, and S. Cowan

Organic Electronics, Feb 2011

Abstract PDF

The series resistance of a bulk heterojunction solar cell diode affects the measurement of the voltage dependence of the diode photocurrent, P(V). An empirical model for the effect is described and shows that P(V) can be significantly modified, particularly at high bias voltages. Experimental measurements on PCDTBT:PCBM solar cells with added series resistance demonstrate the effect and confirm the model. The model provides a method to correct the photoconductivity data using measured quantities.
Phys Rev B

Photoconductivity measurements of the electronic structure of organic solar cells

R. A. Street, K. W. Song, J. E. Northrup, and S. Cowan

Physical Review B, Apr 2011

Abstract PDF

Experimental and theoretical studies of the electronic structure of bulk heterojunction (BHJ) organic solar cells are reported. The photoconductivity spectral response of the solar cells has a weak absorption band extending from the band-gap energy down to <1 eV due to charge-transfer optical excitation at the interface between the polymer and the fullerene. The low-energy absorption indicates an exponential band tail of localized states and an absorption model based on the one-electron joint density of electronic states accounts for the data. Transient photoconductivity measurements of the carrier mobility exhibit a temperature-dependent carrier dispersion. Data analysis for the particular case of transport in the BHJ structure is developed. A multiple trapping model of the dispersive transport is consistent with localized band tail states having a comparable density-of-states distribution to those observed by optical absorption. Theoretical calculations of the density of states including disorder in the π-π spacing of the polymer chains also shows exponential band tailing. A density-of-states model is developed from the data and is discussed.
Large Area Circuits for a Hybrid Macroelectronics-Nanoelectronics Active Monitoring System

Katherine Wei Song

Undergraduate Thesis (Princeton University), Apr 2011

Abstract PDF

Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) are critical components for large area electronics, such as displays and sensors, but up until now, their applications in flexible electronics technology has been limited by their low degree of flexibility. Conventional a-Si:H TFTs are made with a stiff, brittle silicon nitride (SiNx) gate dielectric that restricts the overall flexibility of the devices. Recently, a new, compliant SiO2-silicone hybrid material was invented to replace the conventional SiNx in TFTs. This “hybrid” was found to possess the electrical impermeability characteristic of an inorganic SiO2 dielectric as well as the flexibility characteristic of the polymeric silicone. In the first part of this thesis, we describe studies on the flexibility of TFTs made with the new gate dielectric. We find that the replacement of the SiNx gate dielectric in a-Si:H TFTs with the SiO2-silicone hybrid material results in up to a ten fold increase in flexibility. The development of these ultra-flexible a-Si:H TFTs opens the path to new domains for electronics. In addition to being used in flexible displays, flexible a-Si:H TFTs have the potential to be implemented in new environments that are traditionally off limits to conventional electronics. Here, we describe one such application. The target application of our particular system is for structural health monitoring (SHM) of infrastructure, but it may ideally be applied to systems in other environments as well. a-Si:H TFT based large area circuits are combined with nanoscale integrated circuit (IC) chips to form a system that is both computationally efficient and scalable. The second part of this thesis focuses on a “scanning circuit” composed of a-Si:H TFTs that serves as the interface between a nanoscale IC chip and an array of large area sensors. It is designed to accommodate the low power requirements of the system and account for the imbalance between n-channel and p-channel performance in a-Si:H TFTs. The circuit is initially simulated using standard 90nm Generic Process Design Kit models, and once the functionality is confirmed, a TFT model for simulation is created by empirically fitting a SPICE Level 1 MOSFET model to measured TFT output characteristics. Circuit simulations run with this TFT model demonstrate that the scanning circuit is a feasible design in theory. Preliminary experiments on a single scanning block indicate that the circuit can operate at frequencies of 2.5 kHz, which is sufficient for the target frequency of ∼ 1 kHz.

2010

61.3: Amorphous Silicon TFT Technology for Rollable OLED Displays

Sigurd Wagner, Lin Han, Bahman Hekmatshoar, Katherine Song, Prashant Mandlik, Kunigunde H. Cherenack, and James C. Sturm

SID Symposium Digest of Technical Papers, Apr 2010

Abstract PDF

Amorphous silicon thin-film transistors were designed for roll-out OLED screens in hand-held devices. Separate TFTs reached a saturation current of 6 μA/square, an output current half-life extrapolating to 1,000 years, and were rolled to 1 mm diameter. All three parameters set new world records.
17.3: a-Si:H Thin-film Transistors with a New Hybrid Dielectric Highly Stable under Mechanical and Electrical Stress

Lin Han, Katherine Song, Sigurd Wagner, and Prashant Mandlik

SID Symposium Digest of Technical Papers, Apr 2010

Abstract PDF

A resilient, homogeneous, hybrid of silicon dioxide and silicone polymer deposited at room-temperature replaces the conventional, brittle, silicon nitride barrier layer and gate insulator in amorphous silicon thin-film transistors(a-Si:H TFTs) on flexible polyimide foil. The electron field-effect mobility is high at 1.6 cm2/V⋅s, and the threshold voltage shift under high gate bias is comparable to that in conventional a-Si:H/SiNx TFTs fabricated at 300oC. The substhreshold slope is 290 mV/decade. The new transistors are highly flexible, as they can be bent down to 0.5 mm radius (5% strain) in tension and down to 1mm radius (2.5% strain) in compression. These TFTs qualify for roll-out screens of hand-held devices.
(Invited) A New Insulator for Thin-Film Transistor Backplanes and for Flexible Passivation Layers

Lin Han, Katherine Song, Sigurd Wagner, and Prashant Mandlik

In ECS Transactions, Apr 2010

Abstract PDF

We describe a new flexible material that functions as a gate dielectric of amorphous-silicon thin-film transistors, as a passivation layer for plastic substrates, and as an environmental barrier for organic light-emitting diodes. The material is SiO2 with some silicone polymer character. It is deposited, typically at room temperature, from a glow discharge in which a silicone precursor molecule, hexamethyl disiloxane, is oxidized. Films of the material can be made with a broad range of properties, which vary from those of SiO2 to those of plasma-polymerized silicone. Many macroscopic properties of these films suggest that they are homogeneous. We call the films "hybrid."
Appl Phys Lett

Ultraflexible amorphous silicon transistors made with a resilient insulator

Lin Han, Katherine Song, Prashant Mandlik, and Sigurd Wagner

Applied Physics Letters, Jan 2010

Abstract PDF

The conventional, brittle, silicon nitride barrier layer and gate insulator in amorphous silicon thin-film transistors (a-Si:H TFTs) on 50μm thick polyimide foil was replaced by a resilient, homogeneous, hybrid of silicon dioxide and silicone polymer. The transistor structures can be bent down to 0.5 mm radius (5% strain) in tension and down to 1 mm radius (2.5% strain) in compression. This pronounced flexibility shifts the criterion for reversible bending away from a-Si:H TFT backplanes and toward the materials for substrate and encapsulation. It qualifies a-Si:H TFTs for pull-out display screens in handheld devices.

2009

Effects of Mechanical Strain on the Electrical Performance of Amorphous Silicon Thin-Film Transistors with a New Gate Dielectric

Katherine Wei Song, Lin Han, Sigurd Wagner, and Prashant Mandlik

MRS Proceedings, Jan 2009

Abstract PDF

The stiff SiNx gate dielectric in conventional amorphous silicon thin film transistors (TFTs) limits their flexibility by brittle fracture when in tension. We report the effect on the overall flexibility of TFTs of replacing the brittle SiNx gate dielectric with a new, resilient SiO2-silicone hybrid material, which is deposited by plasma enhanced chemical vapor deposition. Individual TFTs on a 50µm-thick polyimide foil were bent to known radii, and measurement of transfer characteristics were made both during strain and after re-flattening. Compared with conventional TFTs made with SiNx, TFTs made with the new hybrid material demonstrated similar flexibility when strained in compression and significantly increased flexibility when strained in tension. Under bending to compressive strain, all TFTs tested delaminated from the substrate for compressive strains greater than 2%. Conventional a-Si:H/SiNx TFTs have been previously found to delaminate at a similar compressive strain. Under bending to tensile strain, the most flexible TFTs made with the new hybrid material that were tested after re-flattening did not exhibit significant changes in transfer characteristics up to strains of 2.5%. Conventional aSi:H/SiNx TFTs have been found to remain functional for strains of up to 0.5%, a value only one-fifth of that for TFTs made with the new hybrid material.