Overlapping-gate buried-channel charge-coupled devices

In this letter the advantages of the overlapping-gate buried-channel charged-coupled devices over the 3-phase metal-gate and resistive-gate buried-channel c.c.d. are discussed and pertinent design considerations for the overlapping-gate c.c.d.s are presented.     

Moat-etched two-phase charge-coupled devices

A novel technique for fabricating two-phase charge-coupled devices is described. The structure requires only thermally grown SiO₂ and makes use of moats etched into the silicon which in conjunction with a single layer metallization achieve small interelectrode spacings and directionality of charge transport. The feasibility of the technique is demonstrated experimentally. The devices fabricated were successfully operated as both digital and analog shift registers. The method described offers certain advantages in ease of fabrication and reliability along with the capability for high speed operation.     

Antialiasing inputs for charge-coupled devices

An input scheme for analog charge-coupled signal-processing devices has been developed that acts as a prefilter to suppress the aliasing frequencies produced by the sampled-data nature of the CCD. Each charge packet injected into the CCD is a sum of several weighted subsamples taken at a multiple of the CCD clock rate. Various approaches that differ in their rates of oversampling and in their time periods over which subsamples are combined have been compared with respect to their usefulness to produce a sharp cutoff prefilter. A particular implementation using only a factor of 2 oversampling but an averaging period that extends over two CCD clock periods results in a good prefilter characteristic and has been applied to a charge-coupled split-electrode transversal filter. Different implementations of the basic scheme and layout considerations are discussed.     

Theory of amorphous-silicon charge-coupled devices

The theory of operation of amorphous-silicon charge-coupled devices has been studied numerically and analytically under the assumption that the localized states in amorphous-silicon are distributed exponentially with respect to energy. The transfer inefficiency ε is found to depend not only on the localized state density but also on the transit time and initial density of signal electrons. The approximate analysis shows thatln(epsilon)is a linear function of logarithmic clock frequency, and that its coefficient is given by the characteristic temperature which represents the steepness of the localized state density distribution in amorphous-silicon.     

Transform coding using charge-coupled devices

A relatively simple discrete-time analogue technique is described by which short sections of waveforms can be reversibly transformed into a different domain by using a continuous, rather than block, mode of working. The chosen transform is set up as a matrix of resistors whose conductances correspond with the Fourier, Walsh, slant etc. basis vectors required.     

Simple model for charge-coupled devices

A theory for charge-coupled devices has been developed, based on the transient nature of charge flow in these devices. It has been shown that the limiting factor in charge-transport processes is that of diffusion, which gives a typical time of 10?8 s for 90% of charge transfer.     

Interlacing in charge-coupled imaging devices

Solid-state imaging devices to be used in commercial broadcast TV or the Picturephone® system have to supply the video information in a 2:1 interlaced timing format. An efficient way to achieve such a readout from charge-coupled area imaging devices of the frame transfer type is described. The resolution cells of the device are elongated in the vertical dimension to extend across the distance corresponding to two scanning lines in the display. For the two fields forming a full frame the charge generated by the incident light is integrated alternately underneath different sets of electrodes. Experimental results obtained on a 64 × 106 element frame transfer array are presented and compared to theory. They show that in a three-phase structure, by alternately integrating the charge underneath electrodes number 1 and numbers 2+3 jointly, the vertical resolution can be improved by about a factor of 2. This results in a limiting resolution in the vertical direction of about 75 percent of that given by the spatial pitch of the transfer cells. The value 75 percent is characteristic of all raster scanned imaging devices and is a result of the line scanned display. The usefulness of this scheme for line imaging devices is also discussed but is dismissed as being inferior to a bilinear approach with separate interdigitated integration sites.     

Interference-rejection filter using charge-coupled devices

An application of c.c.d. is described to realise a multiple-notch filter which can be made to track and remove a periodic interfering signal and its harmonics. It is shown that, to first order, the filter notches are not dependent on incomplete charge transfer.     

Video integration using charge-coupled devices

C.C.D. analogue shift registers are shown to promise a convenient method for video integration and bandwidth compression. The performance of an experimental prototype is described.     

Noise measurements in charge-coupled devices

Measurements of the noise levels at the output of surface and bulk channel charge-coupled devices with three-phase overlapping polysilicon electrodes are presented. Pulser noise, correlated transfer noise, shot noise, dark current noise, and electrical insertion noise at the input have been measured and studied. The dependences of the electrical insertion noise and the transfer noise on charge packet size and clock frequency are discussed in detail and the latter related to interface state densities. New schemes and input circuits for low-noise electrical insertion of the signal charge are discussed. Our measurements indicate that the noise levels due to the intrinsic noise sources (transfer and storage noise) agree with our physical understanding of the device operation. The noise levels due to the extrinsic noise sources (pulser noise and electrical insertion noise) are above the expected theoretical values.     

Signal processing with charge-coupled devices

The purpose of this paper is to discuss applications of charge-coupled devices in signal processing systems. Both analog and digital CCD concepts are considered. Recent developments in high-speed (∼100 MHz) CCD's are discussed, and the uses of high-speed CCD and surface-acoustic wave (SAW) devices together are considered. Examples of the applications of CCD's in electro-optical systems, secure voice communication systems, sonar systems and radar systems are given. Finally, projections for future uses of CCD's in signal processing systems are presented.     

Linear charge injection to charge-coupled devices using capacitive metering

The input circuit of a charge-coupled device has the form of an m.o.s.f.e.t. Linear charge injection has been achieved by the negative feedback caused by a capacitor connected in series with the equivalent source electrode. The capacitor charge is reset between each sampling event. The distortion is similar to that obtained with fill-and-spill techniques, and the input voltage amplitude is more convenient.     

Feed forward due to barrier modulation in charge-coupled devices

A new type of signal degradation, namely feed forward, is shown to exist in charge-coupled devices. This arises because of barrier modulation due to signal charge and the presence of surface states. Feed forward results in a pulse coming out earlier than the main signal pulse. The magnitude of the feed forward pulse was found to be as high as 0.5 percent of the signal charge for a 24½ bit, CCD delay line. Computer calculations have been performed to quantify the effect for the structure. Results obtained with a special clock for different clocking parameters have been explained, based on the existing model of emission of charge from the surface states.     

Application of charge-coupled devices to infrared detection and imaging

A review of infrared sensitive charge-coupled devices (IRCCD) is presented. Operational requirements of typical IRCCD applications are briefly introduced. IRCCD devices are divided into two major categories: a) Monolithic devices, which essentially extend the original CCD concept into the IR. Monolithic IRCCD's discussed include inversion-mode devices (with narrow bandgap semiconductor substrate), accumulation-mode devices (extrinsic wide bandgap semiconductor substrate), and Schottky-barrier devices (internal photoemission), b) Hybrid devices, in which the functions of detection and signal processing are performed in separate but integratable components by an array of IR detectors and a silicon CCD shift register unit. Hybrid IRCCD's discussed include both direct injection devices (in conjunction with photovoltaic IR detectors) and indirect injection devices (in conjunction with pyroelectric and photoconductive devices).     

Novel tapping technique for charge-coupled devices

The letter proposes a useful technique for the nondestructive tapping of charge-coupled devices, with a presentation of both theoretical and experimental results for device operation. The usefulness of the technique lies primarily in its simplicity of fabrication and operation.     

GaAs and related heterojunction charge-coupled devices

A Schottky-barrier gate GaAs charge-coupled device (CCD) technology is described. Experimental devices fabricated in this technology have operated with charge transfer efficiency >0.999/transfer and-have operated at clock frequencyf_{cl} = 500MHz. Implications of this technology in high-speed signal processing and in visible and near-infrared imaging are discussed.     

Experimental results on junction charge-coupled devices

In junction charge-coupled devices (JCCD's) unique possibilities exist for charge injection and charge detection, which make this device an interesting candidate for analog as well as digital applications. Based on potential calculations published earlier, two processes A and B have been designed for fabricating JCCD's. The essential steps for obtaining a smooth channel potential in process A are a very light phosphorus implantation over the whole device and a phosphorus implantation through the same window used to diffuse the p-type gates. In process B, one phosphorus implantation over the whole device is used and V-groove etching provides the separation between the p-type gates. Devices have been realized with different process parameters. Irregularities in the channel potential were measured using special test devices. The best devices in process A have a transfer inefficiency of 10^-5and a charge-handling capability of 5.10¹¹electrons/cm². In this process, with only seven masking steps, bipolar NPN transistors, and n-channel JFET's were also realized. These excellent results have stimulated further research on analog and digital applications of JCCD's.     

A novel configuration for charge-coupled devices

A novel configuration for the c.c.d. is presented which permits rapid matrix multiplication. One suggested application is matrix inversion by the product-form algorithm.     

Thermal carrier generation in charge-coupled devices

The build-up of thermally generated carriers in a charge-coupled device shift register is characterized by constructing a model for the generation inside a single shift-register bit. Using the model, theoretical response curves are constructed for two practical modes of operation where the contribution from the generation of carriers can be substantial. Experiments are presented which confirm all aspects of the theoretical response curves, including the presence of an initial period of reduced generation in one of the two modes. Procedures for determining generation parameters directly from observed CCD characteristics are presented and implemented. One generation parameter, the minority carrier lifetime τ, is determined by employing the CCD connected in a gate-controlled diode configuration; two others, the depleted surface generation velocity s0, and the general shape of the depletion layer, are determined utilizing a curve fitting procedure. The spatial variation in generation rates is also investigated and found to possess a distribution which is skewed positively and not Gaussian.