The optical method to determine oxygen saturation in blood is limited to only tissues that can be transilluminated. With COVID-19 conventional finger pulse oximeters have surged in popularity; however, most studies of patient in-home oxygenation monitoring are conducted using only a few discrete measurement points per day. The status quo provides a single-point measurement and lacks 2D oxygenation mapping capability. We have demonstrated a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.
Over the past several decades, conventional electronic circuits have been used for both analytical and digital logic circuits. Printed electronics has the potential to reduce fabrication complexity of electronic circuits and using lower-cost and large area manufacturing techniques. The performance of film transistors (OTFTS) has also improved and these devices could be applied to circuit applications where the high performance, high speed, and high energy consumption offered by conventional electronics is not needed. Amongst many factors that govern circuit design, the scale factor (W/L) serves as a crucial variable for tuning a circuit performance. Here we present printing techniques developed in order to adjust aspect ratios of printed transistors using solution processed electronic materials on to flexible substrates. By combining high-speed doctor blade and surface energy patterning we can demonstrate arrays of OTFTs that are later integrated to form circuits. In the surface energy patterning process, a hydrophobic self-assembled monolayer is deposited on a plastic substrate, and plasma etching is used to create hydrophilic regions. The desirable ink is deposited on the hydrophilic regions using doctor blading and only hydrophilic regions are patterned with the ink. Device aspect ratios are increased and controlled by patterning intermitted SD electrodes and controlling the size of the semiconductor island. We utilize screen printing method to interconnect devices to demonstrate several circuit designs such as enhancement-load Inverter, NAND and NOR on the same printing batch. We will discuss how machine learning is used to train this circuits and applied to sensing applications.
Here we demonstrate blade coated polymer light-emitting diodes (PLEDs) with different colors on a flexible substrate for optoelectronic sensor applications. Flexible electronics conform well to human body, which makes them favorable for wearable application. Blade coating is an attractive printing scheme to fabricate electronic devices, in that it is simple to configure and has high throughput. Here, surface energy patterning (SEP) is used to blade coat solution at desired areas. This technique reduces the amount of solution wasted through the sides of the blade, as compared to bladecoating without SEP, which leads to highly homogeneous active layer film and relatively consistent device performance. Using this technique, PLEDs with individual colors, red, green and near infrared (NIR) which are known colors that can be used to detect the condition of haemoglobin, are separately fabricated with blade coating. Luminous Efficacy and EQE of the PLEDs at 1Wsr-1m-2 were 42.7mW/W, 10% for Red, 31.2mW/W, 6.3% for Green, and 8.6mW/W, 3.1% for NIR. Also, SEP is further utilized to bladecoat two PLEDs with different colors on one substrate with no significant changes in the performance of the PLEDs. Before fabricating PLEDs for optoelectronic sensors we assessed design parameters such as minimum required flux and ideal distance between the light source and the detector using solid-state components. Based on the experiment, the PLEDs are fabricated to be used in conjunction with a photodiode to perform pulsating photoplethysmogram (PPG) measurements. Furthermore, with the multicolor PLEDs we successfully demonstrate oxygenation measurement.
An empirically based, open source, optoelectronic model is constructed to accurately simulate organic photovoltaic (OPV) devices. Bulk heterojunction OPV devices based on a new low band gap dithienothiophene- diketopyrrolopyrrole donor polymer (P(TBT-DPP)) are blended with PC70BM and processed under various conditions, with efficiencies up to 4.7%. The mobilities of electrons and holes, bimolecular recombination coefficients, exciton quenching efficiencies in donor and acceptor domains and optical constants of these devices are measured and input into the simulator to yield photocurrent with less than 7% error. The results from this model not only show carrier activity in the active layer but also elucidate new routes of device optimization by varying donor-acceptor composition as a function of position. Sets of high and low performance devices are investigated and compared side-by-side.
The combination of organic semiconductors and emerging
solution-dispersible metal and metal oxide nanoparticles
and nanowires enables the fabrication of electronic devices that are fully built from solution. This establishes a new
device-processing platform that, in turn allows integration of functionality in systems not feasible in any
conventional semiconductor technology. Examples of novel applications and systems enabled by this include:
large-area, ultra light and flexible power harvesting,
logic-integrated sensing and memory technologies. In this
paper we discuss the use of organic Thin Film Transistors (TFTs) based on printed solution-processed materials for
displays and memory applications. Polarizable solution-processed dielectrics and polymer semiconductors were
integrated in the fabrication of non-volatile analog memory arrays. The stability of memory TFTs over 7 days was
studied and characterized, and a stable process to achieve all printed TFTs is presented.
In this paper we report on the use of two solution-processable polymeric and molecular n-channel semiconductors for the
fabrication of transistors and CMOS inverters by gravure printing and inkjet printing. Furthermore, the injket-printed
TFT/invertor stability characteristics are analyzed and discussed.
Methods used to deposit and integrate solution-processed materials to fabricate thin film
transistors by ink-jet printing are presented. We demonstrate successful integration of a complete
additive process with the fabrication of simple prototype TFT backplanes on glass and on flexible
plastic substrates, and we discuss the factors that make the process possible. Surface energy control
of the gate dielectric layer allows printing of the metal
source-drain contacts with gaps as small as
10 um as well as the polymer semiconductor whose electronic properties are very sensitive to
surface energy. Silver nanoparticles are used as gate and data metals, and a polythiophene
derivative (PQT-12) is used as the semiconducting layer, and the gate dielectric is a polymer. The
maximum processing temperature used is 150°C, making the process compatible with flexible
substrates. The ION/IOFF ratio is 105-106, and TFT mobilities of 0.05 cm2/Vs were obtained. The electrical stability of the
all-printed transistors was compared to conventional fabrication methods and it is shown to be acceptable for array operation. Here we discuss the yield of the printing process and show arrays that are integrated with E-ink media to form flexible paper-like displays.
A novel jet-printing approach to fabricate thin film transistor (TFT), active matrix backplanes for x-ray imagers is described. The technique eliminates the use of photolithography and has the potential to greatly reduce the array manufacturing cost. We show how jet-printing is used to pattern the layers of the active matrix array and also to deposit semiconductor material. The technique is applied to both amorphous silicon and polymer transistors, and small prototype arrays have been fabricated and tested, including arrays with a high fill factor amorphous silicon p-i-n photodiode layer for indirect detection x-ray imaging applications. The TFT characteristics are excellent, and acquired x-ray images will be presented and compared to those from conventional TFT arrays. The printing process has been extended to flexible substrates which are important for rugged x-ray imagers, using a low temperature amorphous silicon process to accommodate the plastic substrate. Polymer TFT arrays made with jet-printed polymer solutions have also been demonstrated and we present data from arrays, and discuss options for integrating organic photodiodes or direct detection sensors. The opportunities and challenges of using polymer semiconductors in x-ray imaging arrays, are discussed and we show that the TFT performance meets the needs of radiographic imaging, although the radiation hardness and long term degradation are not sufficiently studied.
Well-characterized F8T2 polyfluorene (Dow Chemical) has been prepared with weight average molecular weights (Mw) ranging from about 20,000 to 120,000. This semiconducting polymer has been used by Plastic Logic to fabricate arrays of 4,800 thin film transistors (TFTs) with 50 dpi, to be used as backplanes for active matrix displays. In this paper, the effects that molecular weight and thermal treatment have on the electrical characteristics of F8T2-based TFTs are
reported. First, transistor performance improves with increasing molecular weight, with maximum values of TFT mobility approaching 1x 10-2 cm2 /V-s. Consistently higher mobilities are obtained when the F8T2 semiconductor makes contact with PEDOT/PSS versus gold electrodes. Alignment of F8T2 on a rubbed polyimide substrate is maintained after quenching, as determined by measurement of the dichroic ratios. Early-stage results on the development of inks
based on F8T2 polyfluorene are also reported.