David Braun

Teaching Sustainability Analysis in Electronics Lecture Courses

David Braun — Fri, 27 Jan 2012 15:03:29 PST

Based on positive prior experiences teaching sustainability analysis in electronics laboratory courses, this work explores techniques for teaching sustainability analysis in lecture courses. As difficult as it may seem to incorporate sustainability into integrated circuit courses or other engineering courses, it may prove as easy as asking students to consider how the coursework relates to sustainability issues.

The need to educate students “to design a system, component, or process to meet desired needs within realistic constraints such as economic, environmental, social, political, ethical, health and safety, manufacturability, and sustainability” has gained sufficient value to deserve its own ABET Program Outcome, Criterion 3(c). This work presents a strategy to introduce students to the relevant issues before senior design coursework, thereby providing practice and enabling them to achieve such a program outcome more skillfully in senior level classes. Key practical challenges arise when attempting to add learning content to a one-quarter electronics course already bursting at the seams with conceptually challenging learning outcomes:

1. No extra class time exists in which to insert additional in-class activities; and

2. Few instructors desire the increased workload associated with reading dozens of additional student essays on top of normal assignment grading.

To address the in-class time limitation, this work delivers the sustainability issues content online. To minimize excess faculty workload, this work presents a tool designed to assist faculty to use peer review of writing assignments, even in medium to large courses. Assessment data confirm the students assimilate new sustainability analysis skills.

Teaching Sustainability in Cal Poly Electrical and Computer Engineering Programs

David Braun et al. — Fri, 27 Jan 2012 15:03:26 PST

Teaching Sustainability Analysis in Electrical Engineering Lab Courses

David Braun — Thu, 06 May 2010 09:08:56 PDT

Laboratory courses represent an incompletely tapped opportunity to teach sustainability concepts. This work introduces and evaluates a simple strategy used to teach sustainability concepts in electrical engineering laboratory courses. The technique would readily adapt to other disciplines. The paper presents assessment data and a wiki containing student sustainability analyses.

Electroluminescent Display Device Including Active Polymer Layer

Aemilianus G. J. Staring et al. — Wed, 01 Apr 2009 16:51:29 PDT

Control device for an electroluminescent display device, comprising an active layer of a semiconducting polymer of, for example pixels arranged in the form of a matrix, reducing flicker and crosstalk. The control device may be based on voltage control at which voltages across the pixels are at least 1.6 V, but is preferably based on current control, at which the duration of the data pulses determines the grey level.

Electroluminescent Device Having Electroluminescent Compound and Liquid Crystalline Compound

Rifat A.M. Hikmet et al. — Wed, 01 Apr 2009 16:51:28 PDT

A description is given of an electroluminescent device (1) having an LED structure, which is composed of an active layer (7) of oriented liquid-crystalline and electroluminescent compounds and a transparent positive electrode layer (5) which is preferably made from an electroconductive polymer. By previously rubbing the electrode layer (5) in one direction with a velvet cloth, an orientation is induced in the molecules in the active layer (7), the orientation being frozen by cooling or polymerization. The electroluminescent device (1) emits polarized light whose direction of polarization is parallel to the direction of rubbing.

Electroluminescent Device Comprising a Transparent Structured Electrode Layer Made From a Conductive Polymer

Aemilianus G. J. Staring et al. — Wed, 01 Apr 2009 16:51:27 PDT

A description is given of an electroluminescent (EL) device (1) composed of polymeric LEDs comprising an active layer (7) of a conjugated polymer and a transparent polymeric electrode layer (5) having electroconductive areas (51) as electrodes. Like the active layer (7), the electrode layer (5) can be manufactured in a simple manner by spin coating. The electrode layer (5) is structured into conductive electrodes (51) by exposure to UV light. The electrodes (9) and (51) jointly form a matrix of LEDs for a display. When a flexible substrate (3) is used, a very bendable EL device is obtained.

Fabrication of Visible Light Emitting Diodes Soluble Semiconducting Polymers

Alan J. Heeger et al. — Wed, 01 Apr 2009 16:51:27 PDT

Visible light LEDs are produced having a layer of conjugated polymer which is cast directly from solution or formed as a gel-processed admixture with a carrier polymer. The LEDs can be formed so as to emit polarized light.

Electroluminescent Illumination System

Dirk J. Broer et al. — Wed, 01 Apr 2009 16:51:15 PDT

An illumination system has an active layer which includes an electroluminescent material, the active layer being located between an optically transparent electrode layer and a reflective electrode layer. A reflective polarizer is present at a side of the transparent electrode layer facing away from the active layer. A sub-beam incident on the polarizer and having an unwanted polarization is reflected back to the active layer, where it is again partially depolarized to recover a component having the desired state of polarization. The invention also relates to a flat-panel picture display device which includes such an illumination system.

Visible Light Emitting Diodes Fabricated From Soluble Semiconducting Polymers

Alan J. Heeger et al. — Wed, 01 Apr 2009 16:50:59 PDT

Crosstalk in Passive Matrix Polymer LED Displays

David Braun — Fri, 20 Mar 2009 10:05:00 PDT

Passive matrix displays based on polymer and organic light-emitting diodes (LEDs) suffer from crosstalk, the emission of light from pixels other than those selected. This article explores the topic of crosstalk both with an approximate but analytic model and by means of more exact circuit simulation in order to explain the causes of crosstalk and to quantify the consequences. We conclude that crosstalk has implications for display power consumption.

Nanosecond Transient Electroluminescene from Polymer Light-Emitting Diodes

David Braun et al. — Fri, 20 Mar 2009 10:04:59 PDT

The transient electroluminescence from polymer light-emitting diodes is reported. When the devices are mounted on a microstrip transmission line, the temporal response is limited by the electrode geometry, with rise and fall times below 50 ns. With low duty-cycle pulses (0.5%) the electroluminescence intensity remains proportional to the current at values up to 10 A/cm², two orders of magnitude greater than possible under direct current operation. Since the spectral blue-shift observed at high current levels (with power dissipation above 1 W/cm²) indicates significant sample heating, still higher levels should be possible with proper thermal management.

Schottky Effect at a Metal-Polymer Interface

G. Rikken et al. — Fri, 20 Mar 2009 10:04:58 PDT

We report the observation of the Schottky effect at the interface between a metal and a semiconducting polymer by means of internal photoemission spectroscopy. The bias dependence of the barrier provides information on the electrical properties of the polymer.

Visible Light Emission from Semiconducting Polymer Diodes

David Braun et al. — Fri, 20 Mar 2009 10:04:58 PDT

We report visible light emission from Shottky diodes made from semiconducting polymers, confirming the discovery by the Cambridge group [Nature 347, 539 (1990)]. Our results demonstrate that light-emitting diodes can be fabricated by casting the polymer film from solution with no subsequent processing or heat treatment required. Electrical characterization reveals diode behavior with rectification ratios greater than 104. We propose that tunneling of electrons from the recitifying metal contact into the gap states of the positive polaron majority carriers dominates current flow and provides the mechanism for light emission.

Electroluminescence and Photoluminescene Efficiency of Poly(p-phenylenevinylene) Deriatives

E. Staring et al. — Fri, 20 Mar 2009 10:04:57 PDT

Alkoxy, alkyl, and cyano derivatives of poly(p-phenylenevinylene) [PPV] are used as the emissive layers in light-emitting diodes [LEDs] to obtain luminescence from red to blue. We present the luminescence efficiency for these soluble PPV derivatives. comparing the photoluminescence [PL] yields with the electroluminescence [EL] yields. PL efficiency increases with the fraction of non-conjugated units. EL efficiency depends not only on the radiative recombination efficiency of the emitting material but also on carrier transport to and within the material. Efforts to improve the efficiency and long term stability of these polymer LEDs are challenged by efficient and balanced carrier injection.

Improved Efficiency in Semiconducting Polymer Light-Emitting Diodes

David Braun et al. — Fri, 20 Mar 2009 10:04:57 PDT

We report visible light emission from metal-polymer diodes made from semiconducting polymers, with indium-tin oxide as the “ohmic” contact, and a variety of metals as the barrier metal. Our results, which confirm the discovery by the Cambridge group [Nature347, 539 (1990)], demonstrate that light-emitting diodes can be fabricated by casting the polymer film on indium-tin oxide from solution with no subsequent polymer processing or heat treatment required. Electrical characterization reveals diode behavior with rectification ratios greater than 105 at sufficiently high voltages. Use of an electrode material with low work function leads to more than an order of magnitude improvement in the room-temperature efficiency of the devices. For example, the most efficient devices made with calcium as the rectifying contact display efficiencies of 0.01 photons per electron.

State-of-the-art: in Polymer Light-Emitting Diodes NEOME Polymer LED Mini Symposium (15–17 September 1993, Eindhoven, The Netherlands)

David Braun et al. — Fri, 20 Mar 2009 10:04:56 PDT

A symposium focused on recent progress in the field of polymer light-emitting diodes was held in Eindhoven during the period 15–17 September 1993. The following is a brief summary of highlights of the symposium. There will be no published proceedings.

Semiconducting Polymer-Buckminsterfullerene Heterojunctions: Diodes, Photodiodes, and Photovoltaic Cells

N. S. Sariciftci et al. — Fri, 20 Mar 2009 10:04:54 PDT

The characterization of rectifying heterojunctions (diodes) fabricated from a semiconducting polymer, a soluble derivative of poly(phenylene-vinylene), and buckminsterfullerene, C₆₀, are reported. Rectification ratios in the current versus voltage characteristics exceed 10⁴. When illuminated, the devices exhibit a large photoresponse as a result of photoinduced electron transfer across the heterojunction interface from the semiconducting polymer (donor) onto C₆₀ (acceptor). The photodiode and photovoltaic responses are characterized. Photoinduced electron transfer across the donor-accepted rectifying heterojunction offers potential for photodetector and for solar cell applications.

Electroluminescence and Electrical Transport in Poly(3-Octylthiophene) Diodes

David Braun et al. — Fri, 20 Mar 2009 10:04:54 PDT

We report visible light emission from diodes made from poly(3-octylthiophene). Use of a soluble derivative of polythiophene allows fabrication of the light emitting diodes by casting the polymer film from solution with no subsequent processing or heat treatment required. The devices emit dim red-orange light with relatively low external quantum efficiencies, below 2.5×10⁻⁵ photons per electron at room temperature. Electrical characterization reveals diode behavior with rectification ratios greater than 10². The temperature dependence indicates that tunneling phenomena dominate the charge injection.

Light-Emitting Diodes from Partially Conjugated Poly(p-phenylene vinylene)

C. Zhang et al. — Fri, 20 Mar 2009 10:04:53 PDT

We report the effect of conversion conditions on the device characteristics of poly(p-phenylene vinylene) (PPV) light-emitting diodes. Both electroluminescence and photoluminescence intensities decrease with increasing degree of conversion. Partial conjugation enhances the electroluminescence intensity and gives an efficiency (with Ca as electron-injecting contact) as high as 0.75% photons per electron, about two orders of magnitude more efficient than from similar devices prepared from fully converted PPV. The results of constant current stress measurements suggest that the partially conjugated PPV diode is relatively stable at room temperature.

Method to Optimize Polymer Film Spin Coating for Polymer LED Displays

M. Cecchi et al. — Tue, 17 Mar 2009 10:16:54 PDT

Research and development of displays and image sensors based on semiconducting polymers require design of new polymer materials and evaluation of film properties. Application of statistical methods can expedite process development. Optimizing device performance entails determining the effect of several process parameters, necessitates numerous samples, and may consume more scarce new material than desired. Uniform film thickness, with no voids, pinholes, inhomogeneities, or particulate contamination across the substrate can improve display efficiency and uniformity. After performing and analyzing a two-cubed full-factorial experiment with three replicated center points, this paper concludes that spin velocity and polymer concentration have statistically significant effects on film thickness, film uniformity, and device efficiency. Ramp acceleration does not. Analysis of variance methodology determines the effect of the three spin coating factors and their two-way interactions.