A structure for backside illuminated ultrahigh-speed charge coupled devices (CCDs) designed to improve the light
sensitivity was investigated. The structure's 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.
A feasibility study is presented for an image sensor capable of image capturing at 100 Mega-frames per second (Mfps). The basic structure of the sensor is the backside-illuminated ISIS, the in-situ storage image sensor, with slanted linear CCD memories, which has already achieved 1 Mfps with very high sensitivity. There are many potential technical barriers to further increase the frame rate up to 100 Mfps, such as traveling time of electrons within a pixel, Resistive-Capacitive (RC) delay in driving voltage transfer, heat generation, heavy electro-magnetic noises, etc. For each of the barriers, a countermeasure is newly proposed and the technical and practical possibility is examined mainly by simulations. The new technical proposals include a special wafer with n and p double epitaxial layers with smoothly changing doping profiles, a design method with curves, the thunderbolt bus lines, and digitalnoiseless image capturing by the ISIS with solely sinusoidal driving voltages. It is confirmed that the integration of these technologies is very promising to realize a practical image sensor with the ultra-high frame rate.
We are developing an ultra-high-sensitivity and ultra-high-speed imaging system for bioscience, mainly for imaging of microbes with visible light and cells with fluorescence emission. Scarcity of photons is the most serious problem in applications of high-speed imaging to the scientific field. To overcome the problem, the system integrates new technologies consisting of (1) an ultra-high-speed video camera with sub-ten-photon sensitivity with the frame rate of more than 1 mega frames per second, (2) a microscope with highly efficient use of light applicable to various unstained and fluorescence cell observations, and (3) very powerful long-pulse-strobe Xenon lights and lasers for microscopes. Various auxiliary technologies to support utilization of the system are also being developed. One example of them is an efficient video trigger system, which detects a weak signal of a sudden change in a frame under ultra-high-speed imaging by canceling high-frequency fluctuation of illumination light. This paper outlines the system with its preliminary evaluation results.
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.
This paper outlines a special microscope under development, named "Ultra-high-speed bionanoscope" for ultra-highspeed
imaging in biological applications, and preliminary design of the image sensor, which is the key component in the
system. The ultra-high-speed bionanoscope consists of two major subsystems: a video camera operating at more than 10
Mfps with ultra-high-sensitivity and the special microscope to minimize loss of light for seriously reduced illumination
light energy due to the ultra-high-speed imaging. The ultra-high-frame rate is achieved by introducing a special structure
of a CCD imager, the ISIS, In-situ Storage Image Sensor, invented by Etoh and Mutoh. The ISIS has an array of pixels
each of which equips with a slanted linear CCD storage area for more than 100 image signals for reproduction of
smoothly moving images. The ultra-high-sensitivity of the sensor of less than 10 photons is achieved by introducing
three existing technologies, backside-illumination, cooling, and the CCM, Charge Carrier Multiplication invented by