Maintainers for DoD and commercial industry are required to inspect and perform maintenance operations in confined spaces. Due to the tight volume and small ingress points into these spaces, hazardous environmental conditions including toxic gases, low oxygen levels, and high heat indices are common. Commercial off the shelf (COTS) solutions exist for testing these environmental conditions, but not in a small, wearable form factor with real-time reporting. In this presentation NextFlex will describe how it will fill this gap via a small wearable sensor Arduino®-like platform with integrated, real-time oxygen, VOC, temperature, and humidity monitoring. NextFlex utilizes additive techniques to print conductive traces and antennas while directly attaching silicon dies and components. This flexible hybrid electronic approach produces a high-performance sensor platform with low size weight and power to ease wear by maintainers.
Printed and flexible hybrid electronics is an emerging technology with potential applications in smart labels, wearable electronics, soft robotics, and prosthetics. Printed solution-based materials are compatible with plastic film substrates that are flexible, soft, and stretchable, thus enabling conformal integration with non-planar objects. In addition, manufacturing by printing is scalable to large areas and is amenable to low-cost sheet-fed and roll-to-roll processes. FHE includes display and sensory components to interface with users and environments. On the system level, devices also require electronic circuits for power, memory, signal conditioning, and communications. Those electronic components can be integrated onto a flexible substrate by either assembly or printing. PARC has developed systems and processes for realizing both approaches. This talk presents fabrication methods with an emphasis on techniques recently developed for the assembly of off-the-shelf chips. A few examples of systems fabricated with this approach are also described.
Wireless sensing has broad applications in a wide variety of fields such as infrastructure monitoring, chemistry, environmental engineering and cold supply chain management. Further development of sensing systems will focus on achieving light weight, flexibility, low power consumption and low cost. Fully printed electronics provide excellent flexibility and customizability, as well as the potential for low cost and large area applications, but lack solutions for high-density, high-performance circuitry. Conventional electronics mounted on flexible printed circuit boards provide high performance but are not digitally fabricated or readily customizable. Incorporation of small silicon dies or packaged chips into a printed platform enables high performance without compromising flexibility or cost.
At PARC, we combine high functionality c-Si CMOS and digitally printed components and interconnects to create an integrated platform that can read and process multiple discrete sensors. Our approach facilitates customization to a wide variety of sensors and user interfaces suitable for a broad range of applications including remote monitoring of health, structures and environment. This talk will describe several examples of printed wireless sensing systems. The technologies required for these sensor systems are a mix of novel sensors, printing processes, conventional microchips, flexible substrates and energy harvesting power solutions.
In electronic systems, components often require different supply voltage for operation. In order to meet this requirement and to optimize power consumption for flexible electronics, we demonstrate a pulsed voltage multiplier that boosts the voltage at specific circuit nodes above the supply voltage. A five-stage pulsed voltage multiplier is shown to provide an output voltage up to 18 V from a supply voltage of 10 V, with minimum 10 ms pulse rise time for a 70 pF load.
A key requirement for the pulsed voltage multiplier circuit is low device leakage to boost the output voltage level. To minimize leakage, the composition of the organic semiconducting layer is modified by blending an insulating polymer with the small molecule semiconductor. This modification allows control over the transistor turn-on voltage, which enables low leakage current required for operation of the circuits. The printed multiplier allows a single power source to deliver multiple voltage levels and enables integration of lower voltage logic with components that require higher operating voltage, for example, in the case of recording data into memory cells in sensor tags.
With the recent improvements in printed devices, it is now possible to build integrated circuit systems out of printed devices. The combination of sensor, logic, and rewritable memory will greatly enhance the functionalities of printed electronics. We have demonstrated integrated sensor tags based on organic complementary circuits patterned by inkjet printing. One example is a temperature threshold sensor tag, wherein if the thermistor temperature exceeds a pre-set threshold, the control circuit generates a pulse to write into a nonvolatile ferroelectric memory cell. The trigger temperature is set by adjusting the bias voltage across the thermistor bridge to match the trigger voltage of the printed threshold circuit, and the threshold temperatures has been tuned between 8 °C and 45 °C with a bias voltage below 30V.
Two types of printable conductor and a bilayer gate dielectric are evaluated for use in all-additive, inkjetprinted
complementary OTFTs. The Ag nanoparticle ink based on nonpolar alkyl amine surfactant or stabilizer enables
good charge injection into p-channel devices, but this ink also leaves residual stabilizer that modifies the transistor backchannel
and shifts the turn-on voltage to negative values. The Ag ink based on polar solvent requires dopant
modification to improve charge injection to p-channel devices, but this ink allows the OTFT turn-on voltage to be close
to 0 V. The reverse trend is observed for n-channel OTFTs. For gate insulator, a bilayer dielectric is demonstrated that
combines the advantages of two types of insulator materials, in which a fluoropolymer reduces dipolar disorder at the
semiconductor-dielectric interface, while a high-k PVDF terpolymer dielectric facilitates high gate capacitance. The
dielectric is incorporated into an inverter and a three-stage ring oscillator, and the resulting circuits were demonstrated to
operate at a supply voltage as low as 2 V, with bias stress levels comparable to circuits with other types of dielectrics.
New findings are presented relating to the optimal choice of gate insulators in organic field effect transistors (OFET). It was recently found that some organic semiconductors operate better when low-k materials are used in the gate. This is quite contrary to the conventional trend to use high permittivity dielectrics for low voltage operation. Interaction between the insulator and the semiconductor materials plays an important role in carrier transport. On one hand, the insulator is often responsible for the morphology of the semiconductor layer, but on the other hand it can also change the distribution of states by local polarisation effects. Carrier localisation is enhanced by insulators with large permittivities, due to the random dipole field present at the interface. We have investigated this effect on a number of disordered organic semiconductor materials and show here that the use of low-k materials may lead to improvements in mobility, reduced temperature activation and hysteresis. In particular, the behaviour of the threshold voltage is interesting. The differences in the underlying physics compared to the case of FETs based on band-like semiconductors, is also discussed.