photosite, 3533-element CCD line imager. The chip was designed in 1.2" long silicon, utilizing two-phase two-level polysilicon gate buried channel technology. Quadrilinear shift registers were implemented to achieve the high resolution, while using moderate design rules for better yield. Complete parallel charge transfer was ensured by employing a structure that eliminated the narrow channel effect. Peripheral and video processing circuits were intergrated on the chip.Conventional CCD line imagers use two readout shift registers. The maximum pixel density of this bilinear design is limited by the minimum poly overlap and spacing design rules in the shift registers. The pixel density can be increased by employing a quadrilinear shift register organization' (Figure 1) to relieve these design rule constraints. However, as the imager resolution and the pixel density increase even further, a new limitation arises due to the narrowing of the CCD parallel transfer channels. This is illustrated in Figure 2, curve A, which shows a conventional quadrilinear cell layout. The charge transfer from the inner shift register to the outer shift register is through the field isolated channel A. The inner shift register has essentially no field confinement in the X direction. For an ultra-high resolution imager, the width of channel A, as confined by the field, is very narrow. This causes a reduction of minimum potential due to the narrow channel effect'. A potential barrier that hinders the charge transfer from the inner shift register to channel A is thus created. The measured minimum potential variation versus the channel width for this conventional design is illustrated in Figure 3, curve A. This curve shows that the minimum potential =tarts t o decrease at l o p channel width. At less than 2 p channel vidth the buried channel changes t o the surface channel.A parallel charge transfer technique was devised to eliminate the charge trapping due to the potential barrier; Figure 2, curve B. The design utilizes the barrier gate in the serial transfer direction t o isolate the charge in the parallel transfer direction also. This poly gate isolation is free from bird's beak and field implant encroachment. Therefore, almost no narrow channel effect occurs. The measured minimum potential versus channel width is illustrated in Figure 3, curve B. This curve shows that the minimum potential is constant down to 4 p channel width.Several peripheral and video processing circuits were integrated on chip to achieve lower overall system cost. These include the clock circuits for the charge detection and the sampling, the Function of Quadrilinear CCD Imager", Electronics Letter, 'Herbst. H. and Pfleiderer, H.J., "Modulation Transfer 2Venkateswaran, V., "Effect of Channel Potential Modulation in Narrow Channel CCD Shift Registers", Proc. IEDM,

This paper presents the design method to achieve ultra -high resolution linear imagers.This method utilizes advanced design rules and novel staggered bilinear photo sensor arrays with quadrilinear shift registers. Design constraint in the detector arrays and shift registers are analyzed. Imager architecture to achieve ultra -high resolution is presented.The characteristics of MTF, aliasing, speed, transfer efficiency and fine photolithography requirements associated with this architecture are also discussed.A CCD imager with advanced 1.5 um minimum feature size was fabricated. It is intended as a test vehicle for the next generation small sampling pitch ultra -high resolution CCD imager.Standard double -poly, two -phase shift registers were fabricated at an 8 um pitch using the advanced design rules.A special process step that blocked the source -drain implant from the shift register area was invented.This guaranteed excellent performance of the shift registers regardless of the small poly overlaps. A charge transfer efficiency of better than 0.99995 and maximum transfer speed of 8 MHz were achieved.The imager showed excellent performance. The dark current was less than 0.2 mV /ms, saturation 250 mV, adjacent photoresponse non -uniformity ± 4% and responsivity 0.7 V/ uJ/cm2 for the 8 pm x 6 pm photosensor size.The MTF was 0.6 at 62.5 cycles /mm. These results confirm the feasibility of the next generation ultra -high resolution CCD imagers.

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This paper describes a high resolution CCD multiplexer for focal plane imaging systems. The multiplexer incorporates quadrilinear readout registers to achieve two times the resolution of conventional bilinear structure while using the same design rules. Complete parallel charge transfer are ensured by a novel buried channel poly gate isolation scheme. A monolithic silicon photodiode array of 8µm pitch, 3533 elements was designed with the multiplexer.Video preprocessing circuits of high speed four to one channel stitching, compensated sample and hold and bad pixel deletion were integrated on chip for improved performance. The modulation transfer functions due to the geometry and the transfer inefficiency are discussed. The theoretically calculated total MTF agrees with the experimental result. At Nyquist frequency of 62.5 c/mm the total MTF is better than 0.6 in the absence of the diffusion MTF degradation. The noise spectrum of the CCD and the output amplifier are presented. The RMS noise of the CCD in dark is approximately 0.35 my over 1 MHz bandwidth. The CCD noise increases with light input attributed primarily to the shot noise. The low noise nature of the multiplexer makes it ideal for the high resolution low light level detection applications.