1.1PixelVision, Inc. Sandbox^TM CCDs

To develop a comprehensive understanding of the fundamental principles governing CCD operation, PixelVision has developed an on-going process of successive modeling, process optimization, and characterization. PixelVision deploys this methodology in its Sandbox^TM CCD foundry offering in which a number of CCDs are fabricated using a single mask set. The Sandbox^TM provides the forum for development and evaluation of a number of experimental devices in a single fabrication lot without the expense of multiple mask sets and fabrication cycles. PixelVision has used this same strategy to demonstrate the performance criteria of the low light level, back-illuminated CCD sensor.

Figure 1.1. Two Full-Wafer CCD Designs. One with the Equivalent of 4096 x 4096, 12-micron square pixels (left);
the other with over twenty-eight 652 x 976 element CCDs (right).

Figure 1.1 illustrates two wafer designs that were fabricated on four-inch silicon wafers. The wafer on the left illustrates a 2" x 2" CCD design with the equivalent of 4096 x 4096, 12-micron square pixels. The design requires the full real estate of the four-inch silicon wafer. The right wafer shows a smaller design, a 652 x 976 element, frame transfer design that has 28 CCD die per wafer. As a single processing defect will render a device inoperable, it is easy to understand that the yield (and cost) of a CCD increases as the area of the imager increases. Equally important are the increased complexity of the manufacturing processes, the photolithography techniques, and design parameters, all which change as devices increase in size and density.

The list of CCDs manufactured on PixelVision's SandboxIII and SandboxIV series of wafer designs is shown in Table 1.1. All of the forty CCD architectures were manufactured for back-illuminated CCD operation optimized for the visible and near infrared (VIS), ultraviolet (UV), or soft x-ray (NO). Additionally, front-illuminated CCDs (FR) were fabricated to offer a baseline for comparison – making a total of 160 different CCD designs available for characterization. Considering various operating modes such as progressive scan and interlaced readout modes, well over 300 very different SandboxIII and SandboxIV devices were available for characterization and integration with CCD camera electronics.

PLUTO III

2

2

12

2

2

12

4

2

12

4

2

12

4

2

12

4

2

12

2

2

9

2

2

9

4

2

9

4

2

9

4

2

9

4

2

9

ADAPT

40

1

36

40

1

36

FAST ONE

4

2

18

4

2

18

NIGHTVIDEO

2

2

12

2

2

12

4

2

12

4

2

12

4

2

12

4

2

12

PLUTO IV

2

2

12

2

2

12

4

2

12

4

2

12

4

2

12

4

2

12

KINO1

4

1

12

4

1

12

8

1

12

8

1

12

8

1

12

8

1

12

KINO2

4

2

12

4

2

12

8

2

12

8

2

12

8

2

12

8

2

12

In this paper, we detail the performance of two of the CCD families: 1) PlutoIII, and 2) ADAPT3. The former was chosen because it represents the state of the art in low noise, video rate, low light level CCD sensor designs. Its features include multiple outputs (4 dual stage amplifiers), large format (2048 x 1024 element), low noise (less than 7 electrons rms.), and high frame rate (greater than 40 MHz bandwidth). The baseline PlutoCCD architecture is shown in Table 2-1. The latter, the ADAPT3, was chosen because, as it contains 40 closely spaced output amplifiers, it is an excellent test bed to easily perform orthogonal experiments and to establish manufacturing yields. As the physics and processing limits of CCD amplifiers is approaching theoretical limits, large format CCDs will increasingly rely on multiple output amplifiers for low-noise/low-light-level imaging.