Transparent conductive electrodes are an important part of LCD displays, solar cells, and lightemitting
diodes, but a replacement must be found for indium tin oxide (ITO), which has become
very expensive. One of the prime candidates is ZnO doped with Al, Ga, or In. Here we present a
convenient analytical mobility model that yields donor ND and acceptor NA concentrations from
Hall-effect measurements at a single temperature, including room temperature (RT). This model
includes scattering from phonons and boundary imperfections as well as from ionized impurities and
point defects. We apply it to films grown by pulsed laser deposition at 200 °C in 10 mTorr of pure
Ar. For a film of thickness 275 nm, the Hall-effect measurements yield a RT resistivity ρ = 1.9 x 10-4 Ω-cm, mobility μ = 28 cm2/V-s, and carrier concentration n = 1.1 x 1021 cm-3, and the mobility
model gives ND = 1.6 x 1021 cm-3 and NA = 4.9 x 1020 cm-3. Also, the transmittance is above 90% in
the visible range. Annealing in forming gas gives ρ = 1.5 x 10-4 Ω-cm, mobility μ = 42 cm2/V-s,
carrier concentration n = 1.0 x 1021 cm-3, ND = 1.1 x 1021 cm-3 and NA = 1.0 x 1020 cm-3. If the
compensation ratio K = NA/ND can be maintained at about 0.1, and ND increased to about 3 x 1021
cm-3, then the model predicts a RT resistivity of less than 7 x 10-5 Ω-cm, well below present ITO
values.
In this work, we show the use of single stranded DNA aptamers as selective biorecognition elements in a sensor based
on a field effect transistor (FET) platform. Aptamers are chemically attached to the semiconducting material in the FET
through the use of linker molecules and confirmed through atomic force microscopy and positive target detection.
Highly selective sensing of a small molecule, riboflavin is shown down to the nano-molar level in zinc oxide FET and
micro-molar level in a carbon nanotube FET. High selectivity is determined through the use of negative control target
molecules with similar molecular structures as the positive control targets with little to no sensor response. The goal of
this work is to develop a sensor platform where biorecognition elements can be used to functionalize an array of
transistors for simultaneous sensing of multiple targets in biological fluids.
Nanocrystalline ZnO films prepared by Pulsed Laser Deposition were used to fabricate the first thin film transistors that
operate at microwave frequencies. Unlike more conventional amorphous Si and organic thin film transistors, which are
only suitable for low speed applications, ZnO-based thin film transistors exhibit figure-of-merit device numbers that are
comparable to single crystal transistors. These include on/off ratio of 1012, current density of >400mA/mm and field
effect mobility of 110 cm2/V.s. Parameters, including film growth temperature, gate insulators, and device layout
designs were examined in detail to maximize performance. We have achieved current gain cut-off frequency, fT, and
power gain cut-off frequency, fmax, values of 2.9GHz and 10GHz, respectively with 1.2μm gate length devices
demonstrating that ZnO-based TFTs are suitable for microwave applications.
It is always inspiring to observe how nature effortlessly integrates a myriad of nanoparticles into very complex living and non-living structures. As we increase our engineering skills from making nanoparticles to integrating them into complex but more useful structures, we are tempted to mimic the approaches used in the nature. At first glance, the "natural way" appears to be particularly suited to handling of a very large number of nanoparticles whose local interaction with each other is dominated by their surface properties. Properly functionalized nanoparticles can therefore be expected to self-assemble into predetermined structures simply by providing the right environment. This approach has indeed been successfully employed to construct many interesting structures ranging from photonic bandgap crystals to solar cells. Can we continue to refine these approaches to make more complex structures? Or, is there an ultimate limitation?
In a diverse field such as nanotechnology with much upside potential, it is difficult to predict limitations. Yet, not all technological approaches are equal in terms of achieving sustainable integration techniques for higher value products. We attempt to compare various integration approaches currently used as to their viability for continued progress. Since many self-assembly techniques have counterparts in natural processes, we examine the limitations and the prospects of nanoassembly processes by attempting to learn from the nature. More specifically, the "top-down" and "bottom-up" assembly approaches are examined for their applicability for nanostructure fabrication.
Conference Committee Involvement (2)
Nanosensing: Materials, Devices, and Systems III
11 September 2007 | Boston, MA, United States
Nanomaterial Synthesis and Integration for Sensors, Electronics, Photonics, and Electro-Optics
1 October 2006 | Boston, Massachusetts, United States
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.