Complementary Ring Oscillators Research Articles

Printed organic transistors and complementary ring oscillators operatable at 200 mV

Applications of organic thin-film transistors (OTFTs) include wearable health monitors and next-generation Internet-of-Things systems driven by a small energy-harvesting power supply. Such applications require low voltage and low power consumption organic ICs. In this paper, we demonstrate complementary ICs based on printed p-type and n-type OTFTs operatable at an ultralow supply voltage of 200 mV. For that purpose, threshold voltages were finely tuned by dual-gate structure and self-assembled monolayer. Complementary inverter-based ring oscillators operated at small supply voltages down to 200 mV and exhibited a power consumption as small as 6 pW per stage.

High-speed hybrid complementary ring oscillators based on solution-processed organic and amorphous metal oxide semiconductors

Solution-processed single-crystal organic semiconductors (OSCs) and amorphous metal oxide semiconductors (MOSs) are promising for high-mobility p- and n-channel thin-film transistors (TFTs), respectively. Organic−inorganic hybrid complementary circuits hence have great potential to satisfy practical requirements. However, some chemical incompatibilities between OSCs and MOSs, such as heat and chemical resistance, make it difficult to rationally integrate TFTs based on solution-processed OSC and MOS onto the same substrates. Here, we report a rational integration method based on the solution-processed semiconductors by carefully managing the device configuration and the deposition and patterning techniques from a materials point of view. The balanced high performances as well as the uniform fabrication of the TFTs led to densely integrated five-stage ring oscillators with a short propagation delay of 1.3 µs per stage.

Ultra Low Power Temperature Compensated Complementary Metal Oxide Semiconductor Ring Oscillator in Subthreshold

Low power consumption, low chip area and fabrication in the standard complementary metal oxide semiconductor (CMOS) process are vital requirements for oscillators used in low-cost bio-implantable and wearable devices. Conventional ring oscillators (ROs) are good candidates for using in biomedical applications. However, their oscillation frequency strongly depends on the temperature. In this study, a temperature compensated ring oscillator with low power consumption is proposed. The transistors of the proposed ring oscillator operate in the subthreshold region to achieve a low power and low voltage performance. Since, in the subthreshold region, the oscillation frequency of a conventional ring oscillator increases with increase in the temperature, two current sources are used to power the proposed subthreshold ring oscillator: a temperature independent current source and a complementary to absolute temperature (CTAT) current source. In the proposed circuit, the CTAT current forms a small part of the total supplied current and its duty is to compensate for the oscillation frequency deviation. Two prototypes of the subthreshold ring oscillator were designed and simulated for a target frequency of 1MHz using commercially available 0.18µm RF-CMOS technology. The thermal coefficient (TC) of the uncompensated ring oscillator was 2400 ppm/ºC from -40ºC to 85ºC, though applying the proposed technique reduces the TC of the ring oscillator to 80.4 ppm/ºC with total power consumption as low as 14.5µW.

Ambipolar Organic Field‐Effect Transistors and Complementary Circuits Based on Single Crystals with Alcohol Treatment

AbstractAmbipolar organic field‐effect transistors (OFETs) are promising candidates for compact organic complementary circuits. High and balanced ambipolar mobilities that facilitate high operation speed and simplifying layout designs, as well as symmetric electrodes that minimize fabrication complexity are critical integrities for state‐of‐art ambipolar OFETs. Organic single crystals with intrinsic ambipolar characteristics are ideal active layer materials because of the high molecular ordering and low density of defects, whereas the generally low electron mobility hindered their further implantation. In this work, the highly crystallized 6,13‐bis(triisopropylsilylethynyl) pentacene single crystals are employed and successfully unveiled the intrinsic high electron mobility by a facile alcohol treatment approach. The resulting ambipolar OFETs showed averaged hole and electron mobilities both higher than 1 cm2 V−1 s−1 by a single type of metal electrode. The presented ambipolar OFETs not only improved the static and dynamic performance of ambipolar OFET‐based complementary inverters and ring oscillators by showing a high voltage gain of 186 and a short stage delay time of 0.7 ms, but they also allowed one logic gate to show two logic functions and potentially benefit the design and functionalities of future OFET‐based complementary circuits as well.

Integrated complementary inverters and ring oscillators based on vertical-channel dual-base organic thin-film transistors

Lateral-channel dual-gate organic thin-film transistors have been used in pseudo complementary metal–oxide–semiconductor (CMOS) inverters to control switching voltage. However, their relatively long channel lengths, combined with the low charge carrier mobility of organic semiconductors, typically leads to slow inverter operation. Vertical-channel dual-gate organic thin-film transistors are a promising alternative because of their short channel lengths, but the lack of appropriate p- and n-type devices has limited the development of complementary inverter circuits. Here, we show that organic vertical n-channel permeable single- and dual-base transistors, and vertical p-channel permeable base transistors can be used to create integrated complementary inverters and ring oscillators. The vertical dual-base transistors enable switching voltage shift and gain enhancement. The inverters exhibit small switching time constants at 10 MHz, and the seven-stage complementary ring oscillators exhibit short signal propagation delays of 11 ns per stage at a supply voltage of 4 V.

Flexible Photodetectors: Flexible Light‐to‐Frequency Conversion Circuits Built with Si‐Based Frequency‐to‐Digital Converters via Complementary Photosensitive Ring Oscillators with p‐Type SWNT and n‐Type a‐IGZO Thin Film Transistors (Small 26/2021)

As a system-level photodetector, flexible light-to-frequency conversion circuits (LFCs) are implemented using a-IGZO and SWNT thin-film transistors. Combined with LFC, CMOS-based frequency-to-digital converter is integrated for digitization of analog signal from LFCs. With the better noise immunity on LFCs, the proposed system by Junyoung Song, Sung Hun Jin, and co-workers (article number 2008131) will significantly contribute to the newly conceived Internet-of-Things (IoT) or smart flexible sensor systems.

High-Speed Complementary Integrated Circuit with a Stacked Structure Using Fine Electrodes Formed by Reverse Offset Printing

A reverse offset-printed stacked-structure complementary ring oscillator and operational amplifier (OPA) circuits were constructed on a large-area substrate. Uniform and fine electrodes were fabric...

Compact modelling and SPICE simulation for three-dimensional, inkjet-printed organic transistors, inverters and ring oscillators

We report an in-depth study of three-dimensional (3D) inkjet-printed flexible organic field-effect transistors (FETs) and integrated circuits (ICs), and demonstrate the necessity, the feasibility and the key aspects of modelling-driven design and analysis. In particular, we performed compact modelling of the flexible printed organic FETs to determine transistor parameters from measured electrical characteristics, and to optimize the design of transistors for a balanced inverter. We also conducted a SPICE simulation of both static and dynamic behaviours of flexible printed organic complementary inverters and ring oscillators. This study revealed design rules to guide fabrication of the 3D structure of the inverter. The study also showed that the parasitic capacitances are dominant factors that determine the transient behaviour of the ring oscillator. Our work provides insights that can guide further improvement of flexible printed organic FETs and ICs towards the realisation of increasingly complex organic ICs and unconventional electronic applications.

Low‐Voltage, High‐Frequency Organic Transistors and Unipolar and Complementary Ring Oscillators on Paper

AbstractPaper substrates for flexible, mobile, and disposable electronic applications draw academic and commercial attention due to their many advantages, such as cost efficiency, low weight, mechanical flexibility, and environmental compatibility. For portable electronic applications, it is important that the electronic devices and circuits can be operated with voltages of a few volts, due to the limitations of mobile power supplies, such as solar cells or energy harvesting devices. Here, low‐voltage organic p‐channel and n‐channel transistors as well as unipolar and complementary ring oscillators are fabricated directly on the surface of a banknote. It is demonstrated that low‐power organic integrated circuits on paper substrates can be operated with supply voltages of less than 3 V and with frequencies of several hundred kilohertz. These results emphasize the prospects of organic transistors for smart paper applications.

Below-one-volt organic thin-film transistors with large on/off current ratios

Abstract In many of the applications envisioned for organic thin-film transistors (TFTs), the electrical power will be supplied by small batteries or energy harvesters, which implies that it will be beneficial if the TFTs can be operated with voltages of 1 V or even below 1 V. At the same time, the TFTs should have large on/off current ratios, especially for applications in digital circuits and active matrices. Here we demonstrate p-channel and n-channel organic TFTs fabricated on a flexible plastic substrate that have a turn-on voltage of exactly 0 V, a subthreshold slope of 100 mV/decade, and an on/off current ratio of 2 × 10 5 when operated with gate-source voltages between 0 and 0.7 V. Complementary inverters fabricated using these TFTs have a small-signal gain of 90 and a minimum noise margin of 79% at a supply voltage of 0.7 V. Complementary ring oscillators can be operated with supply voltages as small as 0.4 V.

(Invited) Radiation-Hard Semiconducting Carbon Nanotube Thin-Film Complementary Circuits

Carbon nanotubes (CNTs) have emerged as promising solution-processed semiconductors for a variety of thin-film electronic devices [1-5] and circuits [6-12]. In particular, the development of stable n-type enhancement-mode doping strategies [13] have enabled the fabrication of complementary integrated circuits [14] with sophisticated functionality such as static random access memory (SRAM) [15]. Since carbon nanomaterials are expected to have low interaction cross-sections with high-energy radiation, CNT thin-film circuits may be especially well-suited for satellite and space applications. To assess this potential, this talk will explore the radiation hardness of complementary circuits based on CNT thin-film transistors. Specifically, CNT-based inverter circuits are studied as a function of total ionizing dose (TID) by a Co-60 gamma ray source. In addition to the response of the individual p-type and n-type transistors, overall inverter circuit metrics (e.g., noise margins, gain, and static dissipated power) are monitored as a function of TID. Under realistic dynamic bias conditions, these CNT-based complementary circuits are found to be radiation-hard with deviations from pre-radiation operation by less than 2%. This work thus establishes CNT thin-film circuits as a promising candidate for next-generation satellite and space electronics. [1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing,” Chem. Soc. Rev., 42, 2824 (2013). [2] V. K. Sangwan, R. P. Ortiz, J. M. P. Alaboson, J. D. Emery, M. J. Bedzyk, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Fundamental performance limits of carbon nanotube thin-film transistors achieved using hybrid molecular dielectrics,” ACS Nano, 6, 7480 (2012). [3] M. Engel, M. Steiner, J.-W. T. Seo, M. C. Hersam, and P. Avouris, “Hot spot dynamics in carbon nanotube array devices,” Nano Lett., 15, 2127 (2015). [4] S. Jang, B. Kim, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Short channel field-effect-transistors with inkjet-printed semiconducting carbon nanotubes,” Small, 11, 5505 (2015). [5] B. Kim, K. Liang, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Enhancement of minority carrier injection in ambipolar carbon nanotube transistors using double-gate structures,” Appl. Phys. Lett., 109, 023515 (2016). [6] M. Ha, J.-W. T. Seo, P. L. Prabhumirashi, W. Zhang, M. L. Geier, M. J. Renn, C. H. Kim, M. C. Hersam, and C. D. Frisbie, “Aerosol jet printed, low voltage, electrolyte-gated carbon nanotube ring oscillators with sub-5 µs stage delays,” Nano Lett., 13, 954 (2013). [7] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “High-speed, inkjet-printed carbon nanotube/zinc tin oxide hybrid complementary ring oscillators,” Nano Lett., 14, 3683 (2014). [8] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “Inkjet printed ambipolar transistors and inverters based on carbon nanotube/zinc tin oxide heterostructures,” Appl. Phys. Lett., 104, 062101 (2014). [9] B. Kim, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Complementary D flip-flops based on inkjet printed single-walled carbon nanotubes and zinc tin oxide,” IEEE Electron Device Lett., 35, 1245 (2014). [10] D. Jariwala, V. K. Sangwan, J.-W. T. Seo, W. Xu, J. Smith, C. H. Kim, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Large-area, low-voltage, antiambipolar heterojunctions from solution-processed semiconductors,” Nano Lett., 15, 416 (2015). [11] B. Kim, J. Park, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Voltage-controlled ring oscillators based on inkjet printed carbon nanotubes and zinc tin oxide,” ACS Appl. Mater. Interfaces, 7, 12009 (2015). [12] B. Kim, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Inkjet printed circuits on flexible and rigid substrates based on ambipolar carbon nanotubes with high operational stability,” ACS Appl. Mater. Interfaces, 7, 27654 (2015). [13] M. L. Geier, K. Moudgil, S. Barlow, S. R. Marder, and M. C. Hersam, “Controlled n-type doping of carbon nanotube transistors by an organorhodium dimer,” Nano Lett., 16, 4329 (2016). [14] M. L. Geier, P. L. Prabhumirashi, J. J. McMorrow, W. Xu, J.-W. T. Seo, K. Everaerts, C. H. Kim, T. J. Marks, and M. C. Hersam, “Subnanowatt carbon nanotube complementary logic enabled by threshold voltage control,” Nano Lett., 13, 4810 (2013). [15] M. L. Geier, J. J. McMorrow, W. Xu, J. Zhu, C. H. Kim, T. J. Marks, and M. C. Hersam, “Solution-processed carbon nanotube thin-film complementary static random access memory,” Nature Nanotechnology, 10, 944 (2015).

Organic complementary ring oscillators using a functional polymer interfacial layer for highly improved oscillation frequency

We report the improved oscillation frequency of the organic complementary ring oscillators by balancing mobilities of p- and n-type organic field-effect transistors (OFETs) with a functional polymer interfacial layer. By employing poly (methyl methacrylate) (PMMA) as the interfacial layer, the balanced performance of the p- and n-type OFETs was achieved, which resulted in the improved performance of the complementary inverters. With the PMMA interfacial layer, the noise margin was increased from 35 % to 80 % of 1/2 supply voltage, and the maximum gain was 1.5 times higher than the one of the complementary inverter without the interfacial layer. The oscillation frequency of the organic complementary ring oscillators was remarkably improved from 106.7 Hz to 1.4 kHz. The polymer interfacial layer to balance the performance of p- and n-type OFETs is found to be a simple and efficient way to facilitate the operation of the organic complementary ring oscillators.

(Invited) Stability and Reliability of Carbon Nanotube Thin-Film Circuits

The isolation and scale-up of electronically monodisperse carbon nanotubes (CNTs) have heightened expectations for CNT-based thin-film electronic devices [1-4] and circuits [5-10]. Indeed, significant progress has been reported for individual CNT thin-film transistors (TFTs), ultimately leading to the demonstration of highly integrated CMOS circuits [11] including static random access memory (SRAM) [12]. While the latter demonstration was realized through careful development of encapsulation schemes that suppress oxygen diffusion, the underlying n-type dopants (i.e., benzyl viologen) possess intrinsic limitations that ultimately degrade electronic performance and limit circuit architecture design. This talk will address this stability and reliability issue by introducing alternative organorhodium n-type dopants for CNT TFTs. In addition to providing controlled n-type doping as determined by TFT and Hall effect measurements, this doping scheme is compatible with top-gated CNT TFT designs. The implications of this work for very-large-scale integration (VLSI) will be discussed. [1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing,” Chem. Soc. Rev., 42, 2824 (2013). [2] V. K. Sangwan, R. P. Ortiz, J. M. P. Alaboson, J. D. Emery, M. J. Bedzyk, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Fundamental performance limits of carbon nanotube thin-film transistors achieved using hybrid molecular dielectrics,” ACS Nano, 6, 7480 (2012). [3] M. Engel, M. Steiner, J.-W. T. Seo, M. C. Hersam, and P. Avouris, “Hot spot dynamics in carbon nanotube array devices,” Nano Lett., 15, 2127 (2015). [4] S. Jang, B. Kim, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Short channel field-effect-transistors with inkjet-printed semiconducting carbon nanotubes,” Small, 11, 5505 (2015). [5] M. Ha, J.-W. T. Seo, P. L. Prabhumirashi, W. Zhang, M. L. Geier, M. J. Renn, C. H. Kim, M. C. Hersam, and C. D. Frisbie, “Aerosol jet printed, low voltage, electrolyte-gated carbon nanotube ring oscillators with sub-5 µs stage delays,” Nano Lett., 13, 954 (2013). [6] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “High-speed, inkjet-printed carbon nanotube/zinc tin oxide hybrid complementary ring oscillators,” Nano Lett., 14, 3683 (2014). [7] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “Inkjet printed ambipolar transistors and inverters based on carbon nanotube/zinc tin oxide heterostructures,” Appl. Phys. Lett., 104, 062101 (2014). [8] B. Kim, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Complementary D flip-flops based on inkjet printed single-walled carbon nanotubes and zinc tin oxide,” IEEE Electron Device Lett., 35, 1245 (2014). [9] D. Jariwala, V. K. Sangwan, J.-W. T. Seo, W. Xu, J. Smith, C. H. Kim, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Large-area, low-voltage, antiambipolar heterojunctions from solution-processed semiconductors,” Nano Lett., 15, 416 (2015). [10] B. Kim, J. Park, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Voltage-controlled ring oscillators based on inkjet printed carbon nanotubes and zinc tin oxide,” ACS Appl. Mater. Interfaces, 7, 12009 (2015). [11] M. L. Geier, P. L. Prabhumirashi, J. J. McMorrow, W. Xu, J.-W. T. Seo, K. Everaerts, C. H. Kim, T. J. Marks, and M. C. Hersam, “Subnanowatt carbon nanotube complementary logic enabled by threshold voltage control,” Nano Lett., 13, 4810 (2013). [12] M. L. Geier, J. J. McMorrow, W. Xu, J. Zhu, C. H. Kim, T. J. Marks, and M. C. Hersam, “Solution-processed carbon nanotube thin-film complementary static random access memory,” Nature Nanotechnology, 10, 944 (2015).

Inkjet Printed Single Walled Carbon Nanotubes As Active Semiconductors in Thin-Film Transistors and Circuits

Inkjet printed single walled carbon nanotubes (SWCNTs) can be incorporated as active layers in thin-film transistors with promising performance. When the channel length is much larger than the average nanotube length (~ 1 mm), charge transport takes place through a network of nanotubes and the SWCNT film behaves like an effective medium with a mobility in excess of 25 cm2/V-s, which makes them suitable for a number of applications. In such devices, the on/off current ratio can be very high (> 105). In devices with channel length less than individual nanotube dimensions, we can get high transconductance devices which can be either p- channel or ambipolar depending on the details of the device structure. We will describe in detail characteristics of both types of SWCNT Transistors. The materials combination of inkjet-printed single-walled carbon nanotubes (SWCNTs) and zinc tin oxide (ZTO) is very promising for large-area thin-film electronics. We compare the characteristics of conventional complementary inverters and ring oscillators measured in air (with SWCNT p-channel Thin-film transistors (TFTs) and ZTO n-channel TFTs) with those of ambipolar inverters and ring oscillators comprised of bilayer SWCNT/ZTO TFTs. This is the first such comparison between the performance characteristics of ambipolar and conventional inverters and ring oscillators. The measured signal delay per stage of 140 ns for complementary ring oscillators is the fastest for any ring oscillator circuit with printed semiconductors to date. We also demonstrate novel voltage controlled ring oscillators which are promising for analog to digital conversion circuits.

(Invited) Vlsi Carbon Nanotube Thin-Film Circuits

With the availability of large quantities of electronically monodisperse carbon nanotubes (CNTs) [1], homogeneous semiconducting CNT thin films can be produced through a variety of solution-based methods including vacuum filtration [2], dielectrophoresis [3], evaporation-driven self-assembly [4], aerosol jet printing [5], and inkjet printing [6,7]. Through careful integration of these thin films with high-k gate dielectrics [8], CNT thin-film transistors (TFTs) can achieve device metrics that are competitive with polycrystalline silicon and amorphous oxide semiconductors [9]. Furthermore, with appropriate device geometries, doping schemes, and gate electrode materials, threshold voltage can be tuned to enable enhancement-mode p-type and n-type TFTs, resulting in CNT CMOS logic gates with subnanowatt static power dissipation and full rail-to-rail voltage swing [10]. While these results suggest that very-large-scale integration (VLSI) should be possible for CNT thin-film circuits, further improvements are needed in CNT TFT large-area spatial homogeneity and long-term environmental stability. Towards these ends, this talk will introduce encapsulation schemes and automated measurement strategies that yield wafer-scale CNT TFT arrays with sufficiently tight control over on/off ratio, subthreshold swing, and threshold voltage for VLSI CNT thin-film circuits. Using this methodology, large-area arrays of fully functional CNT TFT static random access memory (SRAM) cells are demonstrated with desirable static noise and write margins. [1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing,” Chem. Soc. Rev., 42, 2824 (2013). [2] A. Behnam, V. K. Sangwan, X. Zhong, F. Lian, D. Estrada, D. Jariwala, A. J. Hoag, L. J. Lauhon, T. J. Marks, M. C. Hersam, and E. Pop, “High-field transport and thermal reliability of sorted carbon nanotube network devices,” ACS Nano, 7, 482 (2013). [3] M. Steiner, M. Engel, Y.-M. Lin, Y. Wu, K. Jenkins, D. B. Farmer, J. J. Humes, N. L. Yoder, J.-W. T. Seo, A. A. Green, M. C. Hersam, R. Krupke, and Ph. Avouris, “High-frequency performance of scaled carbon nanotube array field-effect transistors,” Appl. Phys. Lett., 101, 053123 (2012). [4] T. A. Shastry, J.-W. T. Seo, J. J. Lopez, H. N. Arnold, J. Z. Kelter, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Large-area, electronically monodisperse, aligned single-walled carbon nanotube thin films fabricated by evaporation-driven self-assembly,” Small, 9, 45 (2013). [5] M. Ha, J.-W. T. Seo, P. L. Prabhumirashi, W. Zhang, M. L. Geier, M. J. Renn, C. H. Kim, M. C. Hersam, and C. D. Frisbie, “Aerosol jet printed, low voltage, electrolyte-gated carbon nanotube ring oscillators with sub-5 µs stage delays,” Nano Lett., 13, 954 (2013). [6] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “High-speed, inkjet-printed carbon nanotube/zinc tin oxide hybrid complementary ring oscillators,” Nano Lett., 14, 3683 (2014). [7] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “Inkjet printed ambipolar transistors and inverters based on carbon nanotube/zinc tin oxide heterostructures,” Appl. Phys. Lett., 104, 062101 (2014). [8] Y.-G. Ha, K. Everaerts, M. C. Hersam, and T. J. Marks, “Hybrid gate dielectric materials for unconventional electronic circuitry,” Acc. Chem. Res., 47, 1019 (2014). [9] V. K. Sangwan, R. P. Ortiz, J. M. P. Alaboson, J. D. Emery, M. J. Bedzyk, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Fundamental performance limits of carbon nanotube thin-film transistors achieved using hybrid molecular dielectrics,” ACS Nano, 6, 7480 (2012). [10] M. L. Geier, P. L. Prabhumirashi, J. J. McMorrow, W. Xu, J.-W. T. Seo, K. Everaerts, C. H. Kim, T. J. Marks, and M. C. Hersam, “Subnanowatt carbon nanotube complementary logic enabled by threshold voltage control,” Nano Lett., 13, 4810 (2013).

Materials and fabrication sequences for water soluble silicon integrated circuits at the 90 nm node

Tungsten interconnects in silicon integrated circuits built at the 90 nm node with releasable configurations on silicon on insulator wafers serve as the basis for advanced forms of water-soluble electronics. These physically transient systems have potential uses in applications that range from temporary biomedical implants to zero-waste environmental sensors. Systematic experimental studies and modeling efforts reveal essential aspects of electrical performance in field effect transistors and complementary ring oscillators with as many as 499 stages. Accelerated tests reveal timescales for dissolution of the various constituent materials, including tungsten, silicon, and silicon dioxide. The results demonstrate that silicon complementary metal-oxide-semiconductor circuits formed with tungsten interconnects in foundry-compatible fabrication processes can serve as a path to high performance, mass-produced transient electronic systems.

Fluoropolymer coatings for improved carbon nanotube transistor device and circuit performance

We report on the marked improvements in key device characteristics of single walled carbon nanotube (SWCNT) field-effect transistors (FETs) by coating the active semiconductor with a fluoropolymer layer such as poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE). The observed improvements include: (i) A reduction in off-current by about an order of magnitude, (ii) a significant reduction in the variation of threshold voltage, and (iii) a reduction in bias stress-related instability and hysteresis present in device characteristics. These favorable changes in device characteristics also enhance circuit performance and the oscillation amplitude, oscillation frequency, and increase the yield of printed complementary 5-stage ring oscillators. The origins of these improvements are explored by exposing SWCNT FETs to a number of vapor phase polar molecules which produce similar effects on the FET characteristics as the PVDF-TrFE. Coating of the active SWCNT semiconductor layer with a fluoropolymer will be advantageous for the adoption of SWCNT FETs in a variety of printed electronics applications.

High-Speed, Inkjet-Printed Carbon Nanotube/Zinc Tin Oxide Hybrid Complementary Ring Oscillators

The materials combination of inkjet-printed single-walled carbon nanotubes (SWCNTs) and zinc tin oxide (ZTO) is very promising for large-area thin-film electronics. We compare the characteristics of conventional complementary inverters and ring oscillators measured in air (with SWCNT p-channel field effect transistors (FETs) and ZTO n-channel FETs) with those of ambipolar inverters and ring oscillators comprised of bilayer SWCNT/ZTO FETs. This is the first such comparison between the performance characteristics of ambipolar and conventional inverters and ring oscillators. The measured signal delay per stage of 140 ns for complementary ring oscillators is the fastest for any ring oscillator circuit with printed semiconductors to date.

Fabrication of Stretchable Single‐Walled Carbon Nanotube Logic Devices

The fabrication of a stretchable single-walled carbon nanotube (SWCNT) complementary metal oxide semiconductor (CMOS) inverter array and ring oscillators is reported. The SWCNT CMOS inverter exhibits static voltage transfer characteristics with a maximum gain of 8.9 at a supply voltage of 5 V. The fabricated devices show stable electrical performance under the maximum strain of 30% via forming wavy configurations. In addition, the 3-stage ring oscillator demonstrates a stable oscillator frequency of ∼3.5 kHz at a supply voltage of 10 V and the oscillating waveforms are maintained without any distortion under cycles of pre-strain and release. The strains applied to the device upon deformation are also analyzed by using the classical lamination theory, estimating the local strain of less than 0.6% in the SWCNT channel and Pd electrode regions which is small enough to keep the device performance stable under the pre-strain up to 30%. This work demonstrates the potential application of stretchable SWCNT logic circuit devices in future wearable electronics.

Inkjet-Printing-Based Soft-Etching Technique for High-Speed Polymer Ambipolar Integrated Circuits

Here, we report the so-called soft-etching process based on an inkjet-printing technique for realizing high-performance printed and flexible organic electronic circuits with conjugated polymer semiconductors. The soft-etching process consists of selective etching of the gate made of a dielectric polymer and deposition of another gate dielectric layer. The method enables the use of a more desirable polymer dielectric layer for the p-channel and n-channel organic field-effect transistors (OFETs) in complementary integrated circuits. We fabricated high-performance ambipolar complementary inverters and ring oscillators (ROs) using poly([N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as the active layer as well as poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) and polystyrene ((PS)/P(VDF-TrFE)) as dielectric materials for the p-channel (pull-up transistor) and n-channel (pull-down transistor) OFETs, respectively. The PS dielectric polymer was selectively etched by inkjetting of n-butyl acetate as an orthogonal solvent for P(NDI2OD-T2). Employing this methodology, the five-stage ambipolar ROs with P(NDI2OD-T2) exhibited an oscillation frequency of ∼16.7 kHz, which was much higher than that of non-soft-etched ROs with a single dielectric layer (P(VDF-TrFE); ∼3 kHz).