P-type thin-film transistors (TFTs) using room temperature sputtered tin and copper oxide as a transparent oxide
semiconductor have been produced on rigid and paper substrates. The SnOx films shows p-type conduction presenting a
polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnOx phases, after annealing at 200 °C.
These films exhibit a hole carrier concentration in the range of ≈ 1016-1018 cm-3, electrical resistivity between 101-102
Ωcm, Hall mobility of 4.8 cm2/Vs, optical band gap of 2.8 eV and average transmittance ≈ 85 % (400 to 2000 nm).
Concerning copper oxide CuxO thin films they exhibit a polycrystalline structure with a strongest orientation along (111)
plane. The CuxO films produced between an oxygen partial pressure of 9 to 75% showed p-type behavior, as it was
measured by Hall effect and Seebeck measurements. The bottom gate p-type SnOx TFTs present field-effect mobility
above 1.24 cm2/Vs (including the paper p-type oxide TFT) and an on/off modulation ratio of 103 while the CuxO TFTs
exhibit a field-effect mobility of 1.3×10-3 cm2/Vs and an on/off ratio of 2×102.
In this work we present sputtered multicomponent dielectrics based on mixtures of HfO2 and SiO2. This way it is
possible to get stable amorphous structure up to 800ºC, that does not happen for pure HfO2, for instance, that present a
polycrystalline structure when deposited without any intentional substrate heating. Besides, also the band gap of the
resulting films is increased when compared with pure HfO2 that theoretically is an advantage in getting a suitable band
offset with the semiconductor layer on oxide TFTs. Concerning the electrical characterization, the leakage current on c-Si
MIS structures is low as 10-9 Acm-2 at 10 V. The amorphous structure of the films also lead to better
dielectric/semiconductor interfaces, as suggested by C-V characteristics on GIZO MIS structures, which do not present
strong variation with frequency. On other hand, the dielectric constant decreases due to the incorporation of SiO2 and
Al2O3. Further improvement on insulating and interface characteristics is achieved using multilayer stacks and substrate
bias during deposition.
Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for
electronic applications, mainly driven by low-cost and disposable applications. Adding to this interest, we must
recognize the importance of the wireless auto sustained and low energy consumption electronics dream. This dream can
be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major
biopolymer and of tremendous global economic importance. The recent developments of oxide thin film transistors and
in particular the production of paper transistors at room temperature had contributed, as a first step, for the development
of disposable, low cost and flexible electronic devices. To fulfil the wireless demand, it is necessary to prove the concept
of self powered devices. In the case of paper electronics, this implies demonstrating the idea of self regenerated thin film
paper batteries and its integration with other electronic components. Here we demonstrate this possibility by actuating
the gate of paper transistors by paper batteries. We found that when a sheet of cellulose paper is covered in both faces
with thin layers of opposite electrochemical potential materials, a voltage appears between both electrodes -paper
battery, which is also self-regenerated. The value of the potential depends upon the materials used for anode and
cathode. An open circuit voltage of 0.5V and a short-circuit current density of 1μA/cm2 were obtained in the simplest
structure produced (Cu/paper/Al). For actuating the gate of the paper transistor, seven paper batteries were integrated in
the same substrate in series, supplying a voltage of 3.4V. This allows proper ON/OFF control of the paper transistor.
Apart from that transparent conductive oxides can be also used as cathode/anode materials allowing so the production of
thin film batteries with transparent electrodes compatible with flexible, invisible, self powered and wireless electronics.
Reported herein is a nonvolatile n-type floating gate memory paper field-effect transistor, emphasizing the role of the
paper structure and properties on the device performance recorded such as in the high capacitance per unit area at low
frequencies (>2.5 μFcm-2) and so on the set of high charge retention times achieved (>16000 hours). The device was
built via the hybrid integration of natural cellulose fibers, which act simultaneously as substrate and gate dielectric, using
amorphous indium zinc and gallium indium zinc oxides respectively for the gate electrode and channel layer. This was
complemented by the use of continuous patterned metal layers as source/drain electrodes.
This paper discusses the effect of order and disorder on the electrical and optical performance of ionic oxide semiconductors based on zinc oxide. These materials are used as active thin films in electronic devices such as pn heterojunction solar cells and thin-film transistors. Considering the expected conduction mechanism in ordered and disordered semiconductors the role of the spherical symmetry of the s electron conduction bands will be analyzed and compared to covalent semiconductors. The obtained results show p-type c-Si/a-IZO/poly-ZGO solar cells exhibiting efficiencies above 14%, in device areas of about 2.34 cm2. Amorphous oxide TFTs based on the Ga-Zn-Sn-O system demonstrate superior performance than the polycrystalline TFTs based on ZnO, translated by ION/IOFF ratio exceeding 107, turn-on voltage below 1-2 V and saturation mobility above 25 cm2/Vs. Apart from that, preliminary data on p-type oxide TFT based on the Zn-Cu-O system will also be presented.
In this paper we report the use of a sheet of cellulose fiber-based paper as the dielectric layer used in oxide based
semiconductor thin film field-effect transistors (FETs). In this new approach we are using the cellulose fiber-based
paper in an "interstrate" structure since the device is build on both sides of the cellulose sheet. Such hybrid FETs
present excellent operating characteristics such as high channel saturation mobility (>30 cm2/Vs), drain-source
current on/off modulation ratio of approximately 104, near-zero threshold voltage, enhancement n-type operation
and sub-threshold gate voltage swing of 0.8 V/decade. The cellulose fiber-based paper FETs characteristics have
been measured in air ambient conditions and present good stability. The obtained results outpace those of
amorphous Si TFTs and rival with the same oxide based TFTs produced on either glass or crystalline silicon
substrates. The compatibility of these devices with large-scale/large-area deposition techniques and low cost
substrates as well as their very low operating bias delineates this as a promising approach to attain high-performance
disposable electronics like paper displays, smart labels, smart packaging, RFID and point-of-care systems for self
analysis in bio-applications, among others.
We report here about a computer simulation program, based on a comprehensive physical and numerical model of an a/(mu) c- Si:H p-i-n device, applied to the 2D problem of describing the transport properties within the structure under non- uniform illumination. The continuity equations for holes and electrons together with Poisson's equation are solved simultaneously along the two directions parallel and perpendicular to the junction. The basic semiconductor equations are implemented with a recombination mechanism reflecting the microcrystalline structure of the different layers. The lateral effects occurring within the structure, due to the non-uniformity of the radiation are outlined. The simulation results obtained for different wavelengths of the incident light are compared and shown their dependence on the energy of the radiation. The results of simulating a p- i-n (mu) c-Si:H junctions under non-uniform illumination is that the generated lateral effects depend not only in intensity but also in direction on the wavelength of the incident radiation.
A Linear array Thin Film Position Sensitive Detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3D inspections/measurements. Each element consists on a 1D LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it will be possible to acquire information about an object/surface, through the optical cross- section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).
The aim of this work is to provide the basis for the interpretation, under steady state, of the lateral photoeffect in p-i-n a-Si:H 1D Thin Film Position Sensitive Detectors (1D TFPSD) through an analytical model. The experimental data recorded in 1D TFPSD devices with different performances are compared with the predicted curves and the obtained correlation's discussed.
The introduction into a traditional p.i.n. structure of two defective buffer layers near the p/i and i/n interfaces can improve the device stability and efficiency through an enhancement of the electric field profile at the interfaces and a reduction of the available recombination bulk centers. The defectous layer (`i-layer'), grown at a higher power density, present a high density of the defects and acts as `gettering centers' able to tailor light induced defects under degradation conditions. If the i-layer density of states remains below 1016 eV-1 cm-3 and assuming a Gaussian distribution of defect states, the gettering center distribution will not affect significantly the carrier population but only its spatial distribution. We report here about a device numerical simulation that allows us to analyze the influence of the `i-layer' position, thickness and density of states on the a-Si:H solar cells performances. Results of some systematic simulation rom the ASCA program (Amorphous Solar Cell Analysis), and for different configurations will be presented.
The aim of this work is to present the main optoelectronic characteristics of large area 1D position sensitive detectors based on amorphous silicon p-i-n diodes. From that, the device resolution, response time and detectivity are derived and discussed concerning the field of applications of the 1D thin film position sensitive detectors.
PIN devices based on hydrogenated amorphous silicon (a-Si:H) became fundamental elements of many different types sensors, based on either the transverse or the lateral photovoltaic effect. In the past we have developed a transient technique, called the Flying Spot Technique (FST), based on the lateral photoeffect. FST allows, not only to infer the ambipolar diffusion length but also the effective lifetime of the photogenerated carriers once the light spot velocity and geometry of the structure were known. In this paper we propose to apply this technique backwards in order to detect the path and velocity of an object that is moving in a light source direction. The light reflected back from the object is analyzed through p.i.n. structure being the transient transverse photovoltage dependent on the object movement (position and velocity). Assuming known the transport properties of the material and the geometry of the device and using a triangulation method we show that it is possible to map the object movement. Details concerning material characterization, simulation and device geometry are presented.
A linear array thin film position sensitive detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3-D inspections/measurements. Each element consists on a one- dimensional LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it is possible to acquire information about an object/surface, through the optical cross-section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).
A rectangular dual-axis large area position sensitive detector (PSD), with 5 cm X 5 cm detection area, has been developed by using a hydrogenated amorphous silicon (a-Si:H) PIN photodiode produced by plasma enhanced chemical vapor deposition (PECVD). The requirements needed for the fabrication of these devices are the thickness uniformity of the different layers, the geometry, and the contacts location. In this paper we present results on PSD with special emphasis on the linearity as well as on its response time.
The purpose of this work is to understand how the recombination of carriers generated by light (at several temperatures) can influence the a-Si:H devices quality. Here we report a comparative analysis between the photovoltaic performances of the PIN diodes and the transport properties of their active i-layers under the same degradation conditions.
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