Contact printing of compositionally graded CdS_xSe_1−x nanowire parallel arrays for tunable photodetectors

Takahashi, Toshitake,Nichols, Patricia,Takei, Kuniharu,Ford, Alexandra C,Jamshidi, Arash,Wu, Ming C,Ning, C Z,Javey, Ali IOP Pub 2012 Nanotechnology Vol.23 No.4

<P>Spatially composition-graded CdS<SUB>x</SUB>Se<SUB>1−x</SUB> (x = 0–1) nanowires are grown and transferred as parallel arrays onto Si/SiO<SUB>2</SUB> substrates by a one-step, directional contact printing process. Upon subsequent device fabrication, an array of tunable-wavelength photodetectors is demonstrated. From the spectral photoconductivity measurements, the cutoff wavelength for the device array, as determined by the bandgap, is shown to cover a significant portion of the visible spectrum. The ability to transfer a collection of crystalline semiconductor nanowires while preserving the spatially graded composition may enable a wide range of applications, such as tunable lasers and photodetectors, efficient photovoltaics, and multiplexed chemical sensors.</P>

Carbon nanotube active-matrix backplanes for conformal electronics and sensors.

Takahashi, Toshitake,Takei, Kuniharu,Gillies, Andrew G,Fearing, Ronald S,Javey, Ali American Chemical Society 2011 Nano letters Vol.11 No.12

<P>In this paper, we report a promising approach for fabricating large-scale flexible and stretchable electronics using a semiconductor-enriched carbon nanotube solution. Uniform semiconducting nanotube networks with superb electrical properties (mobility of 20 cm2 V(-1) s(-1) and ION/IOFF of 10(4)) are obtained on polyimide substrates. The substrate is made stretchable by laser cutting a honeycomb mesh structure, which combined with nanotube-network transistors enables highly robust conformal electronic devices with minimal device-to-device stochastic variations. The utility of this device concept is demonstrated by fabricating an active-matrix backplane (128 pixels, physical size of 64 cm2) for pressure mapping using a pressure sensitive rubber as the sensor element.</P>

Parallel Array InAs Nanowire Transistors for Mechanically Bendable, Ultrahigh Frequency Electronics

Takahashi, Toshitake,Takei, Kuniharu,Adabi, Ehsan,Fan, Zhiyong,Niknejad, Ali M.,Javey, Ali American Chemical Society 2010 ACS NANO Vol.4 No.10

<P>The radio frequency response of InAs nanowire array transistors on mechanically flexible substrates is characterized. For the first time, GHz device operation of nanowire arrays is demonstrated, despite the relatively long channel lengths of ∼1.5 μm used in this work. Specifically, the transistors exhibit an impressive maximum frequency of oscillation, <I>f</I><SUB>max</SUB> ∼ 1.8 GHz, and a cutoff frequency, <I>f</I><SUB>t</SUB> ∼ 1 GHz. The high-frequency response of the devices is due to the high saturation velocity of electrons in high-mobility InAs nanowires. The work presents a new platform for flexible, ultrahigh frequency devices with potential applications in high-performance digital and analog circuitry.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2010/ancac3.2010.4.issue-10/nn1018329/production/images/medium/nn-2010-018329_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn1018329'>ACS Electronic Supporting Info</A></P>

Nanowire active-matrix circuitry for low-voltage macroscale artificial skin

Takei, Kuniharu,Takahashi, Toshitake,Ho, Johnny C.,Ko, Hyunhyub,Gillies, Andrew G.,Leu, Paul W.,Fearing, Ronald S.,Javey, Ali Nature Publishing Group, a division of Macmillan P 2010 NATURE MATERIALS Vol.9 No.10

Large-scale integration of high-performance electronic components on mechanically flexible substrates may enable new applications in electronics, sensing and energy. Over the past several years, tremendous progress in the printing and transfer of single-crystalline, inorganic micro- and nanostructures on plastic substrates has been achieved through various process schemes. For instance, contact printing of parallel arrays of semiconductor nanowires (NWs) has been explored as a versatile route to enable fabrication of high-performance, bendable transistors and sensors. However, truly macroscale integration of ordered NW circuitry has not yet been demonstrated, with the largest-scale active systems being of the order of 1??cm<SUP>2</SUP> (refs?11,15). This limitation is in part due to assembly- and processing-related obstacles, although larger-scale integration has been demonstrated for randomly oriented NWs (ref.?16). Driven by this challenge, here we demonstrate macroscale (7?7??cm<SUP>2</SUP>) integration of parallel NW arrays as the active-matrix backplane of a flexible pressure-sensor array (18?19?pixels). The integrated sensor array effectively functions as an artificial electronic skin, capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5??V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5??mm) for over 2,000 bending cycles. This work presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.

Extremely Bendable, High-PerformanceIntegrated CircuitsUsing Semiconducting Carbon Nanotube Networks for Digital, Analog,and Radio-Frequency Applications

Wang, Chuan,Chien, Jun-Chau,Takei, Kuniharu,Takahashi, Toshitake,Nah, Junghyo,Niknejad, Ali M.,Javey, Ali American ChemicalSociety 2012 Nano letters Vol.12 No.3

<P>Solution-processed thin-films of semiconducting carbonnanotubesas the channel material for flexible electronics simultaneously offershigh performance, low cost, and ambient stability, which significantlyoutruns the organic semiconductor materials. In this work, we reportthe use of semiconductor-enriched carbon nanotubes for high-performanceintegrated circuits on mechanically flexible substrates for digital,analog and radio frequency applications. The as-obtained thin-filmtransistors (TFTs) exhibit highly uniform device performance withon-current and transconductance up to 15 μA/μm and 4 μS/μm.By performing capacitance–voltage measurements, the gate capacitanceof the nanotube TFT is precisely extracted and the corresponding peakeffective device mobility is evaluated to be around 50 cm<SUP>2</SUP>V<SUP>–1</SUP>s<SUP>–1</SUP>. Using such devices, digitallogic gates including inverters, NAND, and NOR gates with superiorbending stability have been demonstrated. Moreover, radio frequencymeasurements show that cutoff frequency of 170 MHz can be achievedin devices with a relatively long channel length of 4 μm, whichis sufficient for certain wireless communication applications. Thisproof-of-concept demonstration indicates that our platform can serveas a foundation for scalable, low-cost, high-performance flexibleelectronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-3/nl2043375/production/images/medium/nl-2011-043375_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl2043375'>ACS Electronic Supporting Info</A></P>

Nanoscale Semiconductor “X” on Substrate “Y” – Processes, Devices, and Applications

Madsen, Morten,Takei, Kuniharu,Kapadia, Rehan,Fang, Hui,Ko, Hyunhyub,Takahashi, Toshitake,Ford, Alexandra C.,Lee, Min Hyung,Javey, Ali WILEY‐VCH Verlag 2011 ADVANCED MATERIALS Vol.23 No.28

<P><B>Abstract</B></P><P>Recent advancements in the integration of nanoscale, single‐crystalline semiconductor ‘X’ on substrate ‘Y’ (XoY) for use in transistor and sensor applications are presented. XoY is a generic materials framework for enabling the fabrication of various novel devices, without the constraints of the original growth substrates. Two specific XoY process schemes, along with their associated materials, device and applications are presented. In one example, the layer transfer of ultrathin III–V semiconductors with thicknesses of just a few nanometers on Si substrates is explored for use as energy‐efficient electronics, with the fabricated devices exhibiting excellent electrical properties. In the second example, contact printing of nanowire‐arrays on thin, bendable substrates for use as artificial electronic‐skin is presented. Here, the devices are capable of conformably covering any surface, and providing a real‐time, two‐dimensional mapping of external stimuli for the realization of smart functional surfaces. This work is an example of the emerging field of “<I>translational nanotechnology</I>” as it bridges basic science of nanomaterials with practical applications.</P>

High-Performance Single Layered WSe₂ p-FETs with Chemically Doped Contacts

Fang, Hui,Chuang, Steven,Chang, Ting Chia,Takei, Kuniharu,Takahashi, Toshitake,Javey, Ali American Chemical Society 2012 Nano letters Vol.12 No.7

<P>We report high performance p-type field-effect transistors based on single layered (thickness, ∼0.7 nm) WSe<SUB>2</SUB> as the active channel with chemically doped source/drain contacts and high-κ gate dielectrics. The top-gated monolayer transistors exhibit a high effective hole mobility of ∼250 cm<SUP>2</SUP>/(V s), perfect subthreshold swing of ∼60 mV/dec, and <I>I</I><SUB>ON</SUB>/<I>I</I><SUB>OFF</SUB> of >10<SUP>6</SUP> at room temperature. Special attention is given to lowering the contact resistance for hole injection by using high work function Pd contacts along with degenerate surface doping of the contacts by patterned NO<SUB>2</SUB> chemisorption on WSe<SUB>2</SUB>. The results here present a promising material system and device architecture for p-type monolayer transistors with excellent characteristics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-7/nl301702r/production/images/medium/nl-2012-01702r_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl301702r'>ACS Electronic Supporting Info</A></P>