A method of making a structure having a patterned a base layer and useful in the fabrication of optical and electronic devices including bioelectronic devices includes, in one embodiment, the steps of: a) providing a layer of a radiation-sensitive resin; b) exposing the layer of radiation-sensitive resin to patterned radiation to form a base layer precursor having a first pattern of exposed radiation-sensitive resin and a second pattern of unexposed radiation-sensitive resin; c) providing a layer of fluoropolymer in a third pattern over the base layer precursor to form a first intermediate structure; d) treating the first intermediate structure to form a second intermediate structure; and e) selectively removing either the first or second pattern of resin by contacting the second intermediate structure with a resin developing agent, thereby forming the patterned base layer. The method is capable of providing multilayer articles having almost any shape at high resolution without the need for expensive or damaging mechanical or laser cutting.

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Organic electrochemical transistor

The conductivity of an $n$-type semiconductor has been calculated in the region of low-temperature $T$ and low impurity concentration ${n}_{D}$. The model is that of phonon-induced electron hopping from donor site to donor site where a fraction $K$ of the sites is vacant due to compensation. To first order in the electric field, the solution to the steady-state and current equations is shown to be equivalent to the solution of a linear resistance network. The network resistance is evaluated and the result shows that the $T$ dependence of the resistivity is $\ensuremath{\rho}\ensuremath{\propto}\mathrm{exp}(\frac{{\ensuremath{\epsilon}}_{3}}{\mathrm{kT}})$. For small $K$, ${\ensuremath{\epsilon}}_{3}=(\frac{{e}^{2}}{{\ensuremath{\kappa}}_{0}}){(\frac{4\ensuremath{\pi}{n}_{D}}{3})}^{\frac{1}{3}}(1\ensuremath{-}1.35{K}^{\frac{1}{3}})$, where ${\ensuremath{\kappa}}_{0}$ is the dielectric constant. At higher $K$, ${\ensuremath{\epsilon}}_{3}$ and $\ensuremath{\rho}$ attain a minimum near $K=0.5$. The dependence on ${n}_{D}$ is extracted; the agreement of the latter and of ${\ensuremath{\epsilon}}_{3}$ with experiment is satisfactory. The magnitude of $\ensuremath{\rho}$ is in fair agreement with experiment. The influence of excited donor states on $\ensuremath{\rho}$ is discussed.

Impurity Conduction at Low Concentrations.

Low resistivity n-type e-Ga2O3 epilayers were obtained for the first time either by adding silane to the gas phase during the metal organic vapour phase epitaxy deposition or by diffusing Sn in nominally undoped layers after the growth. The highest doping concentrations were few 1018 cm−3 and about 1017 cm−3 for Si and Sn doping, with corresponding resistivity below 1 and 10 Ω cm, respectively. Temperature dependent transport investigation in the range of 10-600 K shows a resistivity behavior consistent with the Mott law, suggesting that conduction through localized states dominates the electrical properties of Si- and Sn-doped samples. For both types of dopants, two different mechanisms of conduction through impurity band states seem to be present, each of them determining the transport behavior at the lower and higher temperatures of the measurement range.

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Si and Sn doping of ε-Ga2O3 layers

Defects related to electrical doping of 4H-SiC by ion implantation

The electrical activation of 1×1020 cm-3 implanted Al in 4H-SiC has been studied in the temperature range 1500 - 1950 °C by the analysis of the sheet resistance of the Al implanted layers, as measured at room temperature. The minimum annealing time for reaching stationary electrical at fixed annealing temperature has been found. The samples with stationary electrical activation have been used to estimate the thermal activation energy for the electrical activation of the implanted Al.

About the Electrical Activation of 1×1020 cm-3 Ion Implanted Al in 4H-SiC at Annealing Temperatures in the Range 1500 - 1950°C

The hole transport properties of heavily doped 4H-SiC (Al) layers with Al implanted concentrations of 3  ×  1020 and 5  ×  1020 cm-3 and annealed in the temperature range 1950-2100 °C, have been analyzed to determine the main transport mechanisms. This study shows that the temperature dependence of the resistivity (conductivity) may be accounted for by a variable range hopping (VRH) transport into an impurity band. Depending on the concentration of the implanted impurities and the post-implantation annealing treatment, this VRH mechanism persists over different temperature ranges that may extend up to room temperature. In this framework, two different transport regimes are identified, having the characteristic of an isotropic 3D VRH and an anisotropic nearly 2D VRH. The latter conduction mechanism appears to take place in a rather thick layer (about 400 nm) that is too large to induce a confinement effect of the carrier hops. The possibility that an anisotropic transport may be induced by a structural modification of the implanted layer because of a high density of basal plane stacking faults (SF) in the implanted layers is considered. The interpretation of the conduction in the heaviest doped samples in terms of nearly 2D VRH is supported by the results of the transmission electron microscopy (TEM) investigation on one of the 5  ×  1020 cm-3 Al implanted samples of this study. In this context, the average separation between basal plane SFs, measured along the c-axis, which is orthogonal to the carrier transport during electrical characterization, appears to be in keeping with the estimated value of the optimal hopping length of the VRH theory. Conversely, no SFs are detected by TEM in a sample with an Al concentration of 1  ×  1019 cm-3 where a 3D nearest neighbor hopping (NNH) transport is observed.

Size effect on high temperature variable range hopping in Al+ implanted 4H-SiC.

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1950°C Post Implantation Annealing of Al+ Implanted 4H-SiC: Relevance of the Annealing Time

A new architecture of organic memristive device is proposed with a double-layered polyelectrolyte, one of which is a biological system that alone drives the memristive behavior. In the device the Physarum polycephalum was used as living organism, the polyaniline as conducting polymer for the source-drain channel. The key choice for the device functioning was the interposition of a biocompatible solid layer between polyaniline and living organism, that must result both electrochemically inert and able to preserve a good electrical conductivity of the polyaniline, notwithstanding the alkaline pH environment required for the surviving of living being, by avoiding strong acids. Pectin with a high degree of methylation and chitosan were tested as interlayer, but only the first one satisfied the essential requirements. It was demonstrated that only when the living organism was integrated in the device, the current-voltage characteristics showed the hysteretic rectifying trends typical of the memristive devices, which however disappeared if the Physarum polycephalum switched to its sclerotic state. The mould resulted to survive a series of at least three cycles of voltage-current measurements carried out in sequence.

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Polysaccarides-based gels and solid-state electronic devices with memresistive properties: Synergy between polyaniline electrochemistry and biology

In this work, we confirm and extend the results of a previous study where a variable range hopping transport through localized impurity states has been found to dominate the electrical transport properties of 3×1020 cm-3 and 5×1020 cm-3 Al+ implanted 4H-SiC layers after 1950-2000 °C post implantation annealing. In this study, samples with longer annealing times have been taken into account. The temperature dependence of these sample conductivity follows a variable range hopping law, consistent with a nearly two-dimensional hopping transport of non-interacting carriers that in the highest doped samples, persists up to around room temperature. This result indicates that the hole transport becomes strongly anisotropic on increasing the doping level. At the origin of this unusual electrical behavior, may be the presence of basal plane stacking faults, actually observed by transmission electron microscopy in one of the 5×1020 cm-3 samples

High Temperature Variable Range Hopping in Heavy Al Implanted 4H-SiC

This study shows that, after annealing at 1950°C, a 1×1020 cm-3 Al+ implanted 4H-SiC material shows a decreasing resistivity with increasing annealing time in the range 5-25 min. After this, the resistivity remains constant up to an annealing time of 40 min. The estimated minimum time to gain the thermal equilibrium in this implanted material at 1950°C is 12 min. Electrical characterization has been performed in the 20-680 K temperature range.

Antonella Parisini

Papers

Size effect on high temperature variable range hopping in Al+ implanted 4H-SiC.

1950°C Post Implantation Annealing of Al+ Implanted 4H-SiC: Relevance of the Annealing Time

Polysaccarides-based gels and solid-state electronic devices with memresistive properties: Synergy between polyaniline electrochemistry and biology

High Temperature Variable Range Hopping in Heavy Al Implanted 4H-SiC

1950°C annealing of Al+ implanted 4H-SiC: Sheet resistance dependence on the annealing time