SESSION XIII: OPTOELECTRONIC CIRCUITS
`
`THPM 13.6: Interline CCD Image Sensor with an Anti Blooming Structure
`
`Yasuo Ishihara, Eiji Oda, Hiroshi Tanigawa, Nobukazu Teranishi, Ei-ichi Takeuchi, lkuo Akiyama, Kou-ichi Arai,
`
`Miyo Nishimura, Taka0 Kamata
`
`Nippon Etectric Co., Ltd
`
`Kawasaki, Japan
`
`size is 23 x 13.5pm; chip size is 10 x 7.9mm, applicable to 2/3“
`vidicon camera lenses. The number of picture elements is
`38q H) x 490( V).
`In Figure 3, the relation between VM and VCJJB, which is
`necessary to suppress blooming, is shown for the VOD CCD
`sensor. A reproduced image without blooming was obtained from
`a scene including an incandescent lamp as shown in Figure 4.
`Blooming was not observed until more than lo3 times the satura-
`tion exposure.
`The ratio of the smeared signal to the total signal under 10%
`vertical height illumination, as a function of incident light wave-
`length, is shown in Figure 5. The solid line is for the VOD CCD
`sensor and the broken line is for a device without the VOD. The
`latter was made on a P-type silicon substrate, using the same
`photomasks as the VOD CCD sensor with the conventional fabri-
`cation technology’. An improvement of more than 20 times has
`been achieved for the sensor in the whole wavelength range, since
`signal charges generated in the fully depleted 1PW hardly diffuse
`into the neighboring V-CCDs, because the 1PW potential is always
`higher than that of the surrounding P+ channel stop regions, as
`well as that of 2PW.
`Spectral responses of photosensitivity are shown in Figure 6.
`The near infrared response of the sensor is lowered due to the
`decrease in the effective photosensitive layer thickness. As a
`result, the spectral response of the sensor reaches a similarity to
`the spectrum luminous efficiency curve and permits a reduction of
`the IR-cut filter thickness, to minimize energy loss in the visible
`range. No charge-transfer efficiency and blemish differences were
`found between the VOD CCD sensor and the device without the
`VOD.
`Characteristics are summarized in Table 1.
`
`Acknowledgments
`The authors wish to thank H. Shiraki, A. Kohno and other
`staff members for their technical assistance.
`
`Parameter
`
`
`
`
`
`Saturation Output Voltage
`
`
`
`
`
`THE APPLICATION OF AN overflow drain and barrier positioned
`beside the photosensitive area’ has made it possible to suppress
`blooming of CCD image sensors. However, this method was found
`to sacrifice photosensitivity and dynamic range. This paper will
`describe an interline CCD sensor where the vertical overflow drain
`is positioned under, rather than beside the photodiode. Thus the
`cell area can now be used effectively for photoelectron generation
`and storage, and increased photosensitivity and dynamic range
`can be maintained. Furthermore, this technique eliminates the
`blooming phenomenon.
`A unit cell cross-sectional view of the vertical overflow drain
`(VOD) CCD image sensor is shown in Figure 1. The cell consists
`of a photodiode (PD) and a half stage of a 4-phase driven buried
`channel vertical CCD register (V-CCD) including a threshold con-
`trolled transfer gate (TG) region. The PD is made in a lightly
`doped P-well (lPW), while the rest of the cell is made in a more
`highly doped thick P-well(2PW). N-type substrate is reverse
`biased at VSUB from these grounded P-wells.
`The potential profiles under the PD and the TG region are
`shown in Figure 2(a) for two operating periods of V-CCD clock
`pulse (@v) which is shown in Figure 2(b). T1 and T2 are charge
`transfer and charge integration periods, respectively. During TI,
`as the photogenerated signal charges are transferred to the corres-
`ponding V-CCD, the N-region of the PD is reset at $TGH (TG
`channel potential at @V = VH) as shown by the curve indicated
`as Empty. During the following charge integration period T2, PD
`potential decreases with increasing signal charges. In time, the PD
`potential reaches ($PB + $bi) where $ p ~
`is the minimum poten-
`tial in a completely depleted 1PW corresponding to the supplied
`VSUB and $bi is the built-in potential of the PD junction. When
`VSUB is adjusted in such a way that ( $PB + $bi) is always higher
`than $TGM (TG channel potential at @V = V,) as shown by the
`curve indicated as Full, all of the photogenerated excess charges
`are drained into the N-type substrate, without flowing into the
`V-CCD. As a result, the overflow blooming is suppressed under
`strong illumination.
`
`
`
`Current
`
`The device was fabricated on a 20 - 30C2-cm N-type silicon
`
`0.5
`
`substrate using double-layer polysilicon technology. The 1PW
`and 2PW were made by boron ion implantation. The unit cell
`
`‘Furukawa, A., Matsunaga, Y., Suzuki, N., Harada, N., Endo,
`Y., Hayashimoto, H., Sato, S., Egawa, Y., and Yoshida, 0.. “An
`Interline Transfer CCD for Single Sensor 2/3” Color Camera”,
`IEDM Digest of Technical Papers, p. 346-349; Dec., 1980.
`Teranishi, N., Kohno, A.,
`‘Ishihara, Y., Takeuchi, E.,
`Aizawa, T., Arai, K.. and Shiraki, H., “CCD Image Sensor for
`Single Sensor Color Camera”, ISSCC DIGEST OF TECHNICAL
`PAPERS, p. 24-25; Feb.. 1980.
`
`
`
`V
`
`nA
`
`Lux. sed2856 K)
`
`TVLIPH
`
`dB
`
`electrons
`
`1.0
`
`0.2
`
`280
`
`480
`
`72
`
`65
`
`
`
`Dark
`
`
`
`
`
`Saturation Exposure
`
`Llrnitlng Resolution
`
`Horizontal
`
`TVLIPH
`
`
`
`Vertical
`
`Signal to Noise Ratio
`
`Noise Equivalent Electrons
`
`TABLE 1-Characteristics of the vertical overflow drain CCD
`image sensor.
`
`Magna 2050
`TRW v. Magna
`IPR2015-00436
`
`0001
`
`

`
`Light
`
`?v Photo Shield
`
`C
`
`I
`
`i P W
`
`N-Substrate
`
`"M
`
`FIGURE 1-Cross sectional view of a unit cell for vertical
`overflow drain CCD image sensor.
`
`vSU B
`
`I
`
`Blooming
`Suppression
`
`Y
`
`m
`3
`>
`10 -
`
`d ,
`0
`
`?
`
`,
`5
`( v )
`VM
`FIGURE 3-Relation between VM and VSUB required
`suppress blooming.
`
`( b )
`FIGURE 2-(a) Potential profiles under the PD and the TG
`region, and (b) one of the V-CCD clock pulses h.
`
`10
`
`to
`
`[See page 314for Figure 6.1
`
`/'Without VODl
`
`3
`
`700
`600
`500
`Wave Length (nm)
`FIGURE 5-Percentages of smeared signal as a function of FIGURE 4-Reproduced
`
`incident
`
`800
`
`light
`
`image for VSUB = 6V, VH = 12 V,
`V ~ = 3 v a n d V ~ = - 4 V .
`
`0002
`
`

`
`BA
`
`B' C
`
`C'
`
`FIGURE 6-Cross sectional view of buried drain structure.
`
`0.20
`
`3
`6
`
`\ - 0.15
`
`x
`.-
`-w
`>
`.-
`-I- .-
`v) g 0.10
`
`Ln
`
`iw Without VOD
`
`/
`,d
`/-
`
`,P'
`
`n I
`I
`I
`1
`I
`"400 500 600 700 800 900
`Wave Length ( n m l
`FIGURE 6-Spectral responses of photosensitivity.
`
`0003