Organic Photoconductive Film Research Articles

Organic photoconductive film–stacked active pixel sensor pixel circuits using indium–tin–zinc-oxide thin-film transistors

In this study, we describe the signal readout capabilities of indium–tin–zinc-oxide (ITZO) thin-film transistor (TFT)-based active pixel sensor (APS) pixel circuits combined with organic photoconductive films (OPFs). A pixel circuit was fabricated with a size of 50 μm containing three ITZO TFTs having a channel length of 2 μm and a blue-sensitive OPF possessing excellent properties with an external quantum efficiency of ∼59% and a dark current density of <100 pA cm−2. Signal readout operation of the pixel circuits in accordance with irradiated light intensity was demonstrated, and sufficient response speeds within the line selection period, assuming a pixel number of 320 × 240 (QVGA) at 60 frames per second (∼69.4 μs), was also confirmed by fabricating pixel line arrays comprising 320 and 240 pixels. Our findings show that the miniaturized ITZO TFTs have potential for use in high-pixel-density TFT-based APS image sensors with improved imaging quality.

Advanced features of layered-structure organic-photoconductive-film CMOS image sensor: Over 120 dB wide dynamic range function and photoelectric-conversion-controlled global shutter function

We have developed organic photoconductive film (OPF) CMOS image sensors with pixel structures different from those of a conventional silicon image sensors, in which, the organic thin film for photoelectric conversion and the charge storage part for signal charge accumulation are completely independent. In this paper, we focus on two unique features of the OPF image sensor: (1) technology that realizes over 120 dB simultaneous-capture wide dynamic range, (2) global shutter technology achieving high saturation signals per unit square that is 10 dB higher than that of silicon image sensors with the global shutter function, without sacrificing pixel area. In addition, we have developed a test chip that realizes a high resolution of 8K4K, a high frame rate of 60 fps, a high saturation signals of 450 ke−, and the global shutter function simultaneously. These features of the OPF image sensor will contribute to significant progress in imaging and sensing fields.

A Real-Time Ultraviolet Radiation Imaging System Using an Organic Photoconductive Image Sensor.

We have developed a real time ultraviolet (UV) imaging system that can visualize both invisible UV light and a visible (VIS) background scene in an outdoor environment. As a UV/VIS image sensor, an organic photoconductive film (OPF) imager is employed. The OPF has an intrinsically higher sensitivity in the UV wavelength region than those of conventional consumer Complementary Metal Oxide Semiconductor (CMOS) image sensors (CIS) or Charge Coupled Devices (CCD). As particular examples, imaging of hydrogen flame and of corona discharge is demonstrated. UV images overlapped on background scenes are simply made by on-board background subtraction. The system is capable of imaging weaker UV signals by four orders of magnitude than that of VIS background. It is applicable not only to future hydrogen supply stations but also to other UV/VIS monitor systems requiring UV sensitivity under strong visible radiation environment such as power supply substations.

Image Sensor with Organic Photoconductive Films by Stacking Red/Green and Blue Components

Image Sensor with Organic Photoconductive Films by Stacking Red/Green and Blue Components

Highly Sensitive Organic Photoconductor Using Boron Sub-2,3-naphthalocyanine as a Red-sensitive Film for Stack-type Image Sensors

ABSTRACTBoron sub-2,3-naphthalocyanine chloride (SubNc) was investigated as a potential red-sensitive organic photoconductive film (OPF). A photoconductive cell was fabricated, and its current–voltage characteristics, both with and without light irradiation, and external quantum efficiency (EQE) were determined. The structure of the photoconductive cell was as follows, with thicknesses in nm given in parentheses: glass substrate/In–Zn–O (100)/spiro-2CBP (30)/SubNc (50)/Alq3 (30)/Al (50) (spiro-2CBP = 2,7-bis(carbazol-9-yl)-9,9-spirobifluorene; Alq3 = tris(8-hydroxyquinolinato)aluminum). The spiro-2CBP and Alq3 layers were inserted between the SubNc layer and the electrodes to block dark current injection. The three organic layers were successively deposited by evaporation in a vacuum on the In–Zn–O-patterned substrate. SubNc film absorbed light in the red region well, with an absorption peak at 695 nm. The EQE of the cell reached 80% when the applied bias was 15 V. In addition, the blocking layers effectively suppressed dark current in the OPF, which corresponded to a current density of 20 nA/cm2 at 15 V. These results indicate that SubNc is a promising candidate as a red-sensitive OPF.

Study on Fabrication and Characteristics Analysis of a Red Light-Sensitive Organic Photoconductive Film for a Stacked Color Image Sensor

Study on Fabrication and Characteristics Analysis of a Red Light-Sensitive Organic Photoconductive Film for a Stacked Color Image Sensor

7-2 亜鉛フタロシアニンとC60を用いた有機光導電膜の特性評価(第7部門 情報センシング・コンシューマエレクトロニクス・情報ディスプレイ)

7-2 亜鉛フタロシアニンとC60を用いた有機光導電膜の特性評価(第7部門 情報センシング・コンシューマエレクトロニクス・情報ディスプレイ)

9-1 撮像デバイス用有機光導電膜へのC60添加による分光感度スペクトルへの影響(第9部門 センシング1)

9-1 撮像デバイス用有機光導電膜へのC60添加による分光感度スペクトルへの影響(第9部門 センシング1)

Integrating Multiple Resistive Memory Devices on a Single Carbon Nanotube

AbstractNano‐objects would be of great interest for the development of new types of electronic circuits if one could combine their nanometer scale with original functionalities beyond the conventional transistor action. However, the associated circuit architectures will have to handle the increasing variability and defect rate intrinsic to the nanoscale. In this context, there is a very fast growing interest for memory devices, and in particular resistive memory devices, used as building blocks in reconfigurable circuits tolerant to defects and variability. It was recently shown that optically gated carbon nanotube field effect transistors (OG‐CNTFETs) based on large assemblies of nanotubes covered by an organic photoconductive thin film can be operated as programmable resistors and thus used as artificial synapses in circuits with function‐learning capabilities. Here, the potential of such approach is evaluated in terms of scalability by integrating and addressing several individually programmable resistances on a single carbon nanotube. In addition, the charge storage mechanism can be controlled at a length scale smaller than the device length allowing to also program the direction in which the current flows. It thus demonstrates that a single nanotube section can combine all‐in‐one the properties of an analog resistive memory and of a rectifying diode with tunable polarity.

A 128×96 Pixel, 50 µm Pixel Pitch Transparent Readout Circuit Using Amorphous In–Ga–Zn–O Thin-Film Transistor Array with Indium–Tin Oxide Electrodes for an Organic Image Sensor

Towards a signal readout circuit for a highly sensitive stack-type image sensor, an entire transparent thin-film transistor (TFT) array using an amorphous In–Ga–Zn–O channel and indium–tin oxide electrodes was fabricated. The pixel pitch and number of pixels were 50 µm and 128×96, respectively. The transmittance of the TFT array for visible light reached up to 85%. The array also showed good switching characteristics. A monochromatic image sensor with a zinc phthalocyanine organic photoconductive film was fabricated using this array, and it produced clear images at 30 frames per second with a resolution corresponding to the pixel number.

A 128×96 Pixel Stack-Type Color Image Sensor: Stack of Individual Blue-, Green-, and Red-Sensitive Organic Photoconductive Films Integrated with a ZnO Thin Film Transistor Readout Circuit

A color image was produced by a vertically stacked image sensor with blue (B)-, green (G)-, and red (R)-sensitive organic photoconductive films, each having a thin-film transistor (TFT) array that uses a zinc oxide (ZnO) channel to read out the signal generated in each organic film. The number of the pixels of the fabricated image sensor is 128×96 for each color, and the pixel size is 100×100 µm2. The current on/off ratio of the ZnO TFT is over 106, and the B-, G-, and R-sensitive organic photoconductive films show excellent wavelength selectivity. The stacked image sensor can produce a color image at 10 frames per second with a resolution corresponding to the pixel number. This result clearly shows that color separation is achieved without using any conventional color separation optical system such as a color filter array or a prism.

A 128×96 Pixel Stack-Type Color Image Sensor: Stack of Individual Blue-, Green-, and Red-Sensitive Organic Photoconductive Films Integrated with a ZnO Thin Film Transistor Readout Circuit

A color image was produced by a vertically stacked image sensor with blue (B)-, green (G)-, and red (R)-sensitive organic photoconductive films, each having a thin-film transistor (TFT) array that uses a zinc oxide (ZnO) channel to read out the signal generated in each organic film. The number of the pixels of the fabricated image sensor is 128×96 for each color, and the pixel size is 100×100 µm2. The current on/off ratio of the ZnO TFT is over 106, and the B-, G-, and R-sensitive organic photoconductive films show excellent wavelength selectivity. The stacked image sensor can produce a color image at 10 frames per second with a resolution corresponding to the pixel number. This result clearly shows that color separation is achieved without using any conventional color separation optical system such as a color filter array or a prism.

Improvement in Photoconductive Properties of Coumarin 30-Evaporated Film by Fullerene Doping for Blue-Sensitive Photoconductors

We fabricated two types of organic photoconductive film consisting of coumarin 30/tris(8-hydroxyquinoline)aluminum (Alq3) and fullerene (C60, 10%) : coumarin 30 (90%)/Alq3 by vacuum evaporation and measured the effect of doping C60 as an electron acceptor on the photoconductive properties of the film. The spectral photoresponse characteristics of both films showed good wavelength selectivity in the blue-light region: the peak wavelength of a coumarin 30 neat film was 410 nm and that of a C60:coumarin 30 codeposited film was 440 nm. The external quantum efficiency of the codeposited film reached 64% at an applied voltage of 10 V, while that of the neat film remained at 10% at its highest. These results clearly indicate that the dissociation of electron-hole pairs at the coumarin 30/C60 interface occurs in the codeposited film.

4.有機光導電膜を積層した撮像デバイスの開発

4.有機光導電膜を積層した撮像デバイスの開発

イメージセンシング技術とその応用 有機光導電膜とＺｎＯ ＴＦＴ回路の積層構造を用いた有機撮像デバイスの原理実証実験

In order to achieve compact Super Hi-Vision color camera without the color separation optical systems, we have been developing a new type of image sensor with three organic photoconductive films sensitive to red(R), green(G) and blue(B). In this paper, we fabricated a stacked organic image sensor with G and R sensitive organic photoconductive films, each of which had readout circuit of zinc oxide (ZnO) thin film transistor (TFT). We successfully demonstrated an image pickup at TV flame rate. The sensor produced a color image with a resolution corresponding to the pixel number of ZnO TFT.

Stacked Image Sensor With Green- and Red-Sensitive Organic Photoconductive Films Applying Zinc Oxide Thin-Film Transistors to a Signal Readout Circuit

A vertically stacked image sensor composed of green (G)- and red (R)-sensitive organic photoconductive films, each having a thin-film transistor (TFT) that uses a transparent zinc oxide (ZnO) channel to read out a signal generated in the organic film, was fabricated. The effective number of pixels of the ZnO-TFT circuits was 1410 (47 times 30), and their pitch was 600 mum. The current on/off ratio and turn-on voltage of the ZnO-TFT were over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and 1.5 V, respectively. The G- and R-sensitive organic photoconductive films showed excellent wavelength selectivity: the peak wavelength of the G-sensitive film was 540 nm, and that of the R-sensitive one was 700 nm. A color image with a resolution corresponding to the number of pixels was obtained by a shooting experiment with the fabricated image sensor, which clearly demonstrated color separation in the depth direction of the image sensor, using a stacked structure of wavelength-selective organic films with ZnO-TFT readout circuits.

Photoconductive Properties of Organic Films Based on Porphine Complex Evaluated with Image Pickup Tubes

We have fabricated two types of organic photoconductive films; a layered structure of tetra(4-methoxyphenyl) porphine cobalt complex (Co–TPP) and bathocuproine (BCP) (target A), and another of Co–TPP, tris-8-hydroxyquinoline aluminum (Alq3) and BCP (target B). The photoconductive properties of each film have been measured using image pickup tubes. The dark current was drastically reduced in target B compared with that in target A at the same applied electric field. The external quantum efficiency reached 20% in target B, which is twenty times higher than that in target A. Image pickup of a test chart from target B at standard TV operation was also demonstrated. High resolution and excellent tone sufficient for television use has been obtained.

Wavelength selectivities of organic photoconductive films: Dye-doped polysilanes and zinc phthalocyanine/tris-8-hydroxyquinoline aluminum double layer

Organic photoconductors sensitive to blue, green, and red light were fabricated using coumarin 6 (C6)-doped poly(m-hexoxyphenyl)phenylsilane (PHPPS), rhodamine 6G (R6G)-doped polymethylphenylsilane (PMPS), and zinc phthalocyanine (ZnPc)/tris-8-hydroxyquinoline aluminum (Alq3) double layer, respectively. Selectivities of the spectral responses of these films were good enough to divide the incident light into three color components, indicating the possibility of color separation without prism for video cameras. The quantum efficiency of a ZnPc/Alq3 double-layer film is over an order of magnitude better than those of C6/PHPPS and R6G/PMPS blend films due to the dissociation of electron–hole pair generated at the interface between ZnPc and Alq3.

Image pickup operation from an organic photoconductive film

Image pickup operation from an organic photoconductive film