Denis L. Heidtmann

Large Area CCD Image Sensors For Scientific Applications

This paper describes the performance of two CCD image sensors of 512x512 and 2048x2048 pixel format. These devices were designed specifically for scientific imaging applications.

Large Format, High Resolution Image Sensors

Tektronix is currently fabricating two very large area charge-coupled-device sensors intended for astronomical and other high performance scientific imaging applications, e.g., medical imaging, fluoroscopy, x-ray imaging, spectrometry, particle detectors, etc. In this paper we discuss the performance requirements for scientific-quality CCDs and then focus on the design of the two Tektronix devices and discuss the progress toward achieving the desired performance. These devices are intended for rear-illuminated applications and have 512 X512 and 2048 X2048 pixel formats. The thinned 10 to 20 pm thick Si membrane is fully supported by a unique glass ceramic substrate. Quantum efficiencies of >70% at 700 nm and >40% at wavelengths <400 nm have been measured on a test device. Dark currents as low as 6 pA/cm2 also have been measured recently.

Dual-Channel Charge-Coupled Device For High Speed Signal Acquisition

The paper describes the design and development of a CCD shift register that can take analog samples of an electrical signal at rates up to 1 x 108 samples/s and provide temporary storage for 1024 samples. It is intended for operation in a fast-in, slow-out mode for capturing high speed electrical transients. The requirements of fast clocking and moderate clock driver power led to the choice of a serial-parallel-serial design. The CCD chip contains four storage arrays that form two differential channels. Differential operation provides good linearity. The two channels can be used independently or multiplexed for sampling at the highest rate. The CCD is of the buried-channel type and uses four-phase clocking on all registers. It is fabricated using a modified NMOS process, with two polysilicon layers to provide an overlapping transfer gate structure. Operating characteristics of the CCD are described, together with its behavior in an instrument environment. For optimum performance the CCD chip is mounted on a hybrid, together with clock driver ICs. Such devices are used in the signal acquisition section of a digital storage instrument that was developed recently.

Effects of transistor geometry on CCD output sensitivity

This paper discusses recent progress in the understanding of the fabrication of low noise floating diffusion output amplifiers for special purpose charge-coupled devices. Emphasis has been given to reducing the total node capacitance and increasing the output sensitivity. Measurements of noise on experimental devices has yielded noise less than 3 electrons rms at 50 kpixel data rate.

Quadrant-CCD star tracker

The characteristics of a quadrant-CCD designed for pointing and tracking are discussed with reference to its use in an adaptive optics program. The quadrant-CCD is used to correct stellar image motion proceeding from atmospheric turbulence by means of a system in which a sensor measures the image offset and sends data to a high-speed tip/tilt mirror. The design and control of the device are detailed, including four 100-micron-square pixels, the quadrant architecture, controller electronics, and data acquisition computer and interface. The transfer function is set forth in the x and y directions, and transfer curves are shown. A laboratory simulation of random image motion was conducted to evaluate the performance of the quadrant-CCD as an image motion sensor, and the experimental results are presented. The suitability of the quadrant-CCD for space-based pointing and tracking uses is demonstrated by this test and two earlier theoretical studies. Some future developments which improve performance capabilities are mentioned.

Traps and Deferred Charge in CCDs

Defects which collect charge and then release it into subsequent pixels are the major problem facing CCD users and manufacturers. These defects are categorized loosely into three groups: design, material, and processing induced traps. This paper discusses the current state of the understanding of these single pixel defects in terms of both experimental characterization and theoretical modelling.

Preliminary Characterization of Two High-Speed, Back-Illuminated CCD Image Sensors

This paper discusses the performance of two new sensors: a 2K×2K and a 4K×4K pixel array. These thinned arrays are intended for high frame rate, scientific applications

Trap Characteristics In Large Area CCD Image Sensors

Detailed measurements and characterization of trap behavior in large area CCDs have been performed. The effect of these defects is to cause a local decrease in the charge transfer efficiency in the affected pixel. Bias-temperature stressing of the device has lead to the conclusion that the source of the traps is in the dielectric. A model is proposed which can explain all the current data.

Large Area Ccd Image Sensors For Scientific Applications

This paper describes the performance of two CCD image sensors of 512x512 and 2048x2048 pixel format. These devices were designed specifically for scientific imaging applications.