H. van Kuijk

A Backside-Illuminated Image Sensor With 200 000 Pixels Operating at 250 000 Frames per Second

In this paper, a high-speed image sensor with very high sensitivity is developed. The high sensitivity is achieved by introduction of backside illumination and charge-carrier multiplication (CCM). The high frame rate is guaranteed by installing the in situ storage image sensor (ISIS) structure on the front side. A test sensor of the BSI-ISIS has been developed and evaluated. It is shown that an image with a very low signal level embedded under the noise floor is recognizable by activating the CCM.

Frame transfer CCDs for digital still cameras: concept, design, and evaluation

Digital still cameras are becoming a widely used alternative for conventional silver-halide cameras. This paper presents first the concept of frame-transfer CCD imagers designed for consumer digital cameras. Next, the different modes of operation are explained in detail and compared with alternative approaches. Finally, extensive evaluation results on four different imagers using this new concept are presented. It will be demonstrated that the flexible modes of operation, the high dynamic range, and excellent optical properties of FT-CCDs make them very suited for this type of electronic imaging.

Back-side-illuminated image sensor with burst capturing speed of 5.2 Tpixel per second

We have developed a back-side-illuminated image sensor with a burst capturing speed of 5.2 Tpixels per second. Its sensitivity was 252 V/lux·s (12.7 times that of a front-side-illuminated image sensor) in an evaluation. Sensitivity of a camera system was 2,000 lux F90. The increased sensitivity resulted from optical and time aperture ratios of 100% and also by increasing from a higher optical utilization ratio. The ultrahigh-speed shooting resulted from the use of in-situ storage image sensor. Reducing the wiring resistance and dividing the image area into eight blocks increased the maximum frame rate to 16.7 million frames per second. The total pixel count was 760 horizontally and 411 vertically. The product of the pixel count and maximum frame rate is often used as a figure of merit for high-speed imaging devices, and in this case, 312,360 multiplied by 16.7 million yields 5.2 Tpixels per second. The burst capturing speed is thus 5.2 Tpixels per second, which is the highest speed achieved in high-speed imaging devices to date.

Development of a 300,000-pixel ultrahigh-speed, high-sensitivity CCD

We are developing an ultrahigh-speed, high-sensitivity broadcast camera that is capable of capturing clear, smooth slow-motion videos even where lighting is limited, such as at professional baseball games played at night. In earlier work, we developed an ultrahigh-speed broadcast color camera1) using three 80,000-pixel ultrahigh-speed, highsensitivity CCDs2). This camera had about ten times the sensitivity of standard high-speed cameras, and enabled an entirely new style of presentation for sports broadcasts and science programs. Most notably, increasing the pixel count is crucially important for applying ultrahigh-speed, high-sensitivity CCDs to HDTV broadcasting. This paper provides a summary of our experimental development aimed at improving the resolution of CCD even further: a new ultrahigh-speed high-sensitivity CCD that increases the pixel count four-fold to 300,000 pixels.

An Ultrahigh-Speed, High-Sensitivity, Portable CCD Color Camera

The authors have been developing ultrahigh-speed, high-sensitivity broadcast cameras that are capable of capturing clear, smooth, slow-motion video even in conditions with limited lighting, such as at professional baseball games played at night. In 2003, the first broadcast color camera using three 80,000-pixel ultrahigh-speed, high-sensitivity charge-coupled devices (CCDs) was developed. This camera is capable of ultrahigh-speed video recording at up to 1,000,000 frames/sec, with about ten times the sensitivity of standard high-speed cameras. It has enabled an entirely new style of presentation for sports broadcasts and science programs. The authors continue research to improve the cameras resolution. This paper discusses the development of the first ever ultrahigh-speed high-sensitivity CCD with 300,000 pixels—a four-fold increase over the previous version, as well as the development of a single-chip portable color camera mounted with this CCD.

Development of ultrahigh-speed CCD with maximum frame rate of 2 million frames per second

We developed a 300,000-pixel ultrahigh-speed CCD with a maximum frame rate of 2,000,000 frames per second. The shooting speed of the CCD was possible by directly connecting CCD memories, which record video images, to the photodiodes of individual pixels. The simultaneous parallel recording operation of all pixels results in the ultimate frame rate. We analyzed a voltage wave pattern in the equivalent circuit model of the ultrahigh-speed CCD by using a SPICE simulator to estimate the maximum frame rate. The pixel area was consisted of 410 and 720 pixels in the vertical and horizontal and divided into 8 blocks for parallel driving. An equivalent circuit of one block was constructed from an RC circuit with 410 × 90 pixels. The voltage wave pattern at the final stage of an equivalent circuit was calculated when a square wave pulse was input. Results showed that the square wave pulse became blunt when the driving speed was increased. After estimation, we designed the layout of the new ultrahigh-speed CCD V6 and fabricated the device. Results of an image capturing experiment indicated a saturation signal level of 100% that was maintained up to 300,000 frames per second. A saturation signal level of 50% was observed in 1,000,000 frames per second and of 13% in 2,000,000 frames per second. We showed that the maximum frame rate is dependent on a drop of the saturation signal level resulting from the driving voltage wave pattern becoming blunt.

A 300-kpixel Ultrahigh-Speed Charge-Coupled Device With a Dynamic Range of 48.6 dB at 1 Million Frames per Second

An ultrahigh-speed charge-coupled device (CCD) with an increased dynamic range at a frame rate above 200 kiloframes per second (kfps) was developed. The dynamic range of a CCD operating at extremely high speeds is reduced as a result of rounding of a sharp voltage waveform inside the device. The amount of rounding was estimated by using an equivalent circuit model of one kind of electrodes in a four-phase CCD memory. The simulation showed that the calculated voltage at a quarter period and the measured saturation signal level have similar dependence on the frame rate. To suppress the drop in voltage at a quarter period, the active pixels and the driving circuit were divided, and the resistance of the pixel wiring was reduced. A new ultrahigh-speed CCD, whose active pixels are divided into eight separately driven blocks and that employs dual wirings to each electrode of the four-phase CCD memory, was designed and fabricated. A driving evaluation experiment showed that the ultrahigh-speed CCD had a dynamic range of 48.6 dB at 1 000 000 fps. This range is equivalent to 8-bit digital and is 2.5 times higher than that of a previous ultrahigh-speed CCD.

An ultrahigh-speed color video camera operating at 1,000,000 fps with 288 frame memories

We developed an ultrahigh-speed color video camera that operates at 1,000,000 fps (frames per second) and had capacity to store 288 frame memories. In 2005, we developed an ultrahigh-speed, high-sensitivity portable color camera with a 300,000-pixel single CCD (ISIS-V4: In-situ Storage Image Sensor, Version 4). Its ultrahigh-speed shooting capability of 1,000,000 fps was made possible by directly connecting CCD storages, which record video images, to the photodiodes of individual pixels. The number of consecutive frames was 144. However, longer capture times were demanded when the camera was used during imaging experiments and for some television programs. To increase ultrahigh-speed capture times, we used a beam splitter and two ultrahigh-speed 300,000-pixel CCDs. The beam splitter was placed behind the pick up lens. One CCD was located at each of the two outputs of the beam splitter. The CCD driving unit was developed to separately drive two CCDs, and the recording period of the two CCDs was sequentially switched. This increased the recording capacity to 288 images, an increase of a factor of two over that of conventional ultrahigh-speed camera. A problem with the camera was that the incident light on each CCD was reduced by a factor of two by using the beam splitter. To improve the light sensitivity, we developed a microlens array for use with the ultrahigh-speed CCDs. We simulated the operation of the microlens array in order to optimize its shape and then fabricated it using stamping technology. Using this microlens increased the light sensitivity of the CCDs by an approximate factor of two. By using a beam splitter in conjunction with the microlens array, it was possible to make an ultrahigh-speed color video camera that has 288 frame memories but without decreasing the cameras light sensitivity.

Simulation based design for back-side illuminated ultrahigh-speed CCDs

A structure for backside illuminated ultrahigh-speed charge coupled devices (CCDs) designed to improve the light sensitivity was investigated. The structures shooting speed of 1 million frames/second was made possible by directly connecting CCD memories, which record video images, to the photodiodes of individual pixels. The simultaneous parallel recording operation of all pixels results in the highest possible frame rate. Because back-side illumination enables a fill factor of 100% and a quantum efficiency of 60%, sensitivity ten or more times that of front-side illumination can be achieved. Applying backside illumination to ultrahigh-speed CCDs can thus solve the problem of a lack of incident light. An n- epitaxial layer/p- epitaxial layer/p+ substrate structure was created to collect electrons generated at the back side traveling to the collection gate. When a photon reaches the deep position near the CCD memory in the p-well, an electron generated by photoelectric conversion directly mixes into the CCD memory. This mixing creates noise, making it necessary to reduce the reach of the incident light. Setting the thickness of a double epitaxial layer to 30 μm, however, will inhibit the generation of this noise. A potential profile for the n-/p-/p+ structure was calculated using a three-dimensional semiconductor device simulator. The transit time from electron generation to arrival at the collection gate was also calculated. The concentrations of the n- and p- epitaxial layers were optimized to minimize transit time, which was ultimately 1.5 ns. This value is adaptive to a frame rate of 100 million frames/second. Charge transfer simulation of a part of the pixel was conducted to confirm the smooth transfer of electrons without their staying too long in one place.

Evaluation of a backside-illuminated ISIS

This paper presents preliminary evaluation results of a test sensor of the backside-illuminated ISIS, an ultra-high sensitivity and ultra-high speed CCD image sensor. To achieve ultra-high sensitivity, the CCD image sensor employs the following three technologies: backside illumination, cooling and Charge Carrier Multiplication (CCM). The test sensor has been designed, fabricated and evaluated. At room temperature without cooling, the video camera has about ten-time higher sensitivity than the previous one, which was supported by a conventional front side illumination technology. Furthermore, the video camera can detect images at very low signal level, less than 5 e-, by using CCM at -40 degree C.