Bucket-brigade Devices Research Articles

Nonoverlapping dual-gate bucket-brigade devices

A novel bucket-brigade charge-transfer device concept is presented and experimentally verified. The dual-gate BBD exhibits operational performances comparable to surface-channel charge-coupled devices, while still enjoying fabrication simplicity and high yield. The concept is implemented using conventional p-channel aluminum-gate technology with only an additional shadowed-gap lift-off process which produces self-aligned bias-gate electrodes separated from the adjacent clock buses by submicron (typically 0.5 μm) spacings. Transfer inefficiencies below 10−4 at 100 kHz and around 5×10−4 at 1 MHz have been currently observed, despite the low carrier mobility (140 cm2/V s).

Modeling and experimental simulation of the low-frequency transfer inefficiency in bucket-brigade devices

The work presented in this paper extends the available theory and it also presents a model for the low-frequency charge transfer in MOS bucket-brigade devices (BBD's). Our new theory which characterizes the low-frequency component of transfer inefficiency in terms of the subthreshold current is frequency independent and it incorporates both channel-length and barrier-height modulations. This model was verified experimentally on simulated BBD's. After proving both theoretically and experimentally that the low-frequency transfer inefficiency of BBD devices is due to subthreshold current, we successfully used this knowledge to design an improved BBD device. This improved device includes only one extra ion-implantation step relative to the original BBD device. An ion implant is used in part of the BBD channel.

Microcomputers do on-chip a-d conversion : Electronics p. 67 (20 July 1978)

In many applications of nanopositioning, such as scanning probe microscopy, tracking fast periodic reference trajectories with high accuracy is highly desirable. Repetitive control is a simple and effective control scheme to obtain good tracking of such reference trajectories. In order to implement repetitive control, a method for introducing time-delay is necessary. This can easily be implemented using a memory buffer with digital signal processing equipment. To achieve fast, high accuracy, and low noise performance, fast microcontrollers or field-programmable gate array hardware with fast high-resolution analog-to-digital and digital-to-analog converters are needed. As an inexpensive alternative to digital signal processing, the use of an analog bucket brigade device to implement the time-delay is investigated in this paper. Bucket brigade devices use switching to carry the input voltage over an array of capacitors, achieving a specified time-delay. Low-noise bucket brigade devices can achieve a signal-to-noise ratio around 80 dB, comparable to the actual performance when using 16-bit analog-to-digital converters. In this paper, the proposed control scheme utilizes a modified integral control law in conjunction with the repetitive control law. The overall control scheme ensures robustness towards plant uncertainty. Experimental results demonstrate the effectiveness of the overall control scheme and the analog implementation.

Free charge propagation in a resistive-gate MOS transmission line

A detailed computer analysis of the charge-transport process in an MOS transmission line (MOSTL)operating in deep depletion is presented. The mathematical model is developed taking into account time-dependent gate voltages, field-dependent surface mobility, and voltage-dependent depletion capacitance. A distributed transmission line circuit model similar to that obtained in a previous work for charge-transfer devices is derived. The charge-propagation characteristics are discussed and interpreted. The contributions of the physical transport mechanisms are investigated from the standpoint of assessing the influence of the design parameters and operating conditions on the performances of the structure. Several driving techniques which use time-varying gate voltages are proposed and simulated. Special emphasis is directed toward the possible improvements in the performances of an MOSTL used as a bit line in a continuously charge-coupled RAM or as a variable delay line for digital signals. Under some simplifying assumptions, an approximate model which yields closed-form solutions for the operational parameters of interest that compare well with the numerical calculations is developed. To a certain extent, the theory derived in this paper is also valid for charge-transfer devices, in particular for the charge-transfer process in bucket-brigade devices and under the transfer gates of two-phase CCD's.

High display viewability provided by thin-film EL, black layer, and TFT drive

This laboratory has recently developed low-voltage thin-film electroluminescent (EL) emitters combining the brightness maintenance characteristics first reported by the Sharp Corporation in 1974 [1] with a new light-absorbing black layer, reminiscent of those introduced by Sigmatron [2],[3]. This combination, together with a new thin-film-EL active-matrix TFT switch configuration, has resulted in highly efficient high-ambient viewability. In addition, brief mention is made of a new approach to display addressing utilizing our newly developed thin-film bucket-brigade device [4].

Effect of transistor parameters on the performance of a bucket-brigade delay unit

This paper studies the effect of transistor parameters on the operation of the bucket-brigade device. For this purpose the transister has been represented by a modified Ebers-Moll madel. It has been found that ur is the most significant factor affecting sample transfer. The nth sample transfer suffers a loss of (l/αt)n. and it has an error expressed by (U — Vj)(l —αtn)where U is the clock voltage and Vj represents the transistor input knee voltage. If at is close to unity and the number of transfers is small, the above quantities are negligible.

The dielectric constant associated with direct interband transitions in germanium : B. G. Martin and R. F. Wallis. Solid St. Commun.21, p. 385 (1977)

With ‘photo-ASICs’ comprising light-sensitive structures, light-emitting devices and analog and digital circuits, complete optical metrology systems can be integrated on a single chip. We report the realization of key components of such photo-ASICs using an industrual IC CMOS process. We achieve photodiodes with an external quantum efficiency of 50–80% in the visible spectrum and position-sensitive devices (PSDs) with a spatial non-linearity of around 0.3%. We demonstrate surface-channel CCDs with a charge-transfer efficiency of 99.8% at room temperature, as well as bucket-brigade devices (BBDs) with a lower charge-transfer efficiency of 96%. Light-emitting diodes (LEDs) are realized, emitting infrared light at 1160 nm (forward biased) and broadband visible yellow light with a spectral maximum at 640 nm (reverse biased). We discuss simple applications of passive photo-ASICs, such as a centroid detector, a 3-D camera, a motion detector and a focus sensor, used to obtain a relative measure for the local focus of an optically imaged scene, for example, in a photographic camera.

A charge-transfer multiplying digital-to-analog converter

A new charge-transfer multiplying digital-to-analog converter employs an array of binary-weighted MOS capacitors and MOS transistors as its only elements. It can be fabricated on the same chip and by the same process as most charge-coupled devices and bucket-brigade devices, and provides two- or four-quadrant multiplication. An experimental n-channel metal-gate MOS realization demonstrated accuracy to 7 bits plus sign, total harmonic distortion 60 dB below fundamental, 70 dB dynamic range, and 200 kHz bandwidth.

Low frequency transfer efficiency of E-beam fabricated conductively connected charge-coupled device

Theoretical calculations are made of low frequency transfer inefficiency for the conductively connected charge-coupled device (C4D). Two mechanisms for transfer inefficiency arise in the C4D which are not found in correctly operated charge-coupled devices (CCD's) but are found in bucket brigade devices. These are 1) barrier length modulation and 2) diffusion over the barrier. Theoretical analyses are made for both of these mechanisms, and both are found to be significant (∼0.05 percent/transfer for a 5/µm barrier) and independent of frequency. The transfer inefficiency increases sharply as feature size is reduced but decreases as oxide thickness is reduced. The fabrication and testing of C4D's with barrier lengths in the range 1.75 µm to 5 µm are described, and the measured transfer inefficiencies compare well with theoretical predictions.

Low frequency transfer efficiency of E-beam fabricated conductively connected charge-coupled device

Theoretical calculations are made of low frequency transfer inefficiency for the conductively connected charge-coupled device (C4D). Two mechanisms for transfer inefficiency arise in the C4D which are not found in correctly operated charge-coupled devices (CCD's) but are found in bucket brigade devices. These are 1) barrier length modulation and 2) diffusion over the barrier. Theoretical analyses are made for both of these mechanisms, and both are found to be significant (~0.05 percent/transfer for a 5 /spl mu/m barrier) and independent of frequency. The transfer inefficiency increases sharply as feature size is reduced but decreases as oxide thickness is reduced. The fabrication and testing of C4D's with barrier lengths in the range 1.75 /spl mu/m to 5 /spl mu/m are described, and the measured transfer inefficiencies compare well with theoretical predictions.

Distributed model analysis of charge-coupled and bucket-brigade devices

The paper suggests a method of investigating from a unitary point of view the operational characteristics of charge-transfer devices. The equations of the model, as well as the voltage-dependent elements of the equivalent circuits, are derived. Solutions for the transfer inefficiency, the distribution of charge in the discharging potential well and for the currents along the channel, obtained by a stable finite-difference scheme, are reported. A reasonable boundary condition in the form of a nonlinear partial differential equation is derived for the bucket-brigade transfer process. The transfer inefficiency parameter for bucket-brigade devices is defined and numerically computed.

Noise in MOS bucket-brigade devices

Previous calculations of noise in bucket-brigade devices (BBD's) have ignored subthreshold leakage current even though BBD's operate in the subthreshold region over most of their useful frequency range. In this work, subthreshold leakage is included in the calculation, but surprisingly, it makes little difference in the end result. The noise spectrum in p-channel BBD's is measured and agrees well with the calculated noise spectrum which includes the effects of correlation between noise packets, imperfect charge transfer efficiency, and output circuitry.

Charge-coupled devices and applications : J. E. Carnes and W. F. Kosonocky. Solid St. Technol. 67 (Apr. 1974)

Testimonial to the importance of the charge-transfer phenomenon is attested to by the Morris N. Liebmann and the David A. Sarnoff awards this year to the originators of the charge-coupled and bucket-brigade devices, respectively. The papers in this session concentrate on the former. Charge-coupled devices are unique among semiconductor elements. In all other device embodiments into circuits, charge is manipulated and extracted and then used to charge a capacitor or passed through a resistor in each case to develop a signal voltage. In charge-coupled devices the signal is contained within the magnitude of the charge packet itself. A key technological problem in CCD relates to the speed and efficiency with which the information in the form of the charge can be transferred from region to region of the device structures. The first three papers of this session will describe advances in the modeling and testing of charge transfer in charge-coupled devices.

Programmable Bandpass Filter and Tone Generator Using Bucket-Brigade Delay Lines

Bucket-brigade devices have been used to build a new type of active filter that is equivalent to a second-order digital filter without the need for complex analog-to-digital conversion. The filter response characteristics, i.e., center frequency and bandwidth, depend on the circuit parameters of gain and clock frequency, both of which may be electronically controlled. By using a variable clock signal, 1023 frequencies can be accurately selected by the proper setting of ten switches. The selected clock frequency uniquely determines the center frequency of the bucket-brigade filter. The programmable feature of the clock circuit, therefore, allows the convenient selection of the center frequency of the bandpass filter. A slight modification to the programmable bandpass filter converts it into a programmable oscillator. Thus, any one of 1023 tones can be generated by the proper setting of the switches. A device that exhibits both filter and oscillator functions has been demonstrated in the laboratory.

A programmable bandpass filter and tone generator using bucket-brigade delay lines

Bucket-brigade devices have been used to build a new type of active filter that is equivalent to a second-order digital filter without the need for complex analog-to-digital conversion. The x It) filter response characteristics, i.e., center frequency and bandwidth, + I depend on the circuit parameters of gain and clock frequency, both e2(t- U of which may be electronically controlled. + By using a variable clock signal, 1023 frequencies can be ac- I e0%, curately selected by the proper setting of ten switches. The selected clock frequency uniquely determines the center frequency of the bucket-brigade filter. The programmable feature of the clock circuit, DELAND therefore, allows the convenient selection of the center frequency u It-T,) of the bandpass filter. A slight modification to the programmable bandpass filter converts it into a programmable oscillator. Thus, any one of 1023 tones can be generated by the proper setting of the switches. A device that ex- D hibits both filter and oscillator functions has been demonstrated in the laboratory.

Transversal filtering using charge-transfer devices

Techniques are presented for making transversal filters using charge-coupled devices and bucket-brigade devices. In a CCD transversal filter, the delayed signals are sampled by measuring the current flowing the clock lines during transfer, and the sampled signals are weighted by a split electrode technique. In a BBD transversal filter, the delayed signals are `tapped' with a source follower whose load determines the weighting coefficient. Examples are given of CCD and BBD filters that are `matched' to particular signalling waveforms, and the limitations of charge-transfer devices in matched filtering applications are discussed. Finally, the application of CTD transversal filters to other signal processing functions is discussed.

Bucket-brigade device with improved charge transfer

The charge transfer of bucket-brigade devices can be considerably improved by the additional use of one transistor and one resistor per cell. The effect of this is demonstrated by a computer simulation.

Charge Transfer Devices

This is a review describing the use of charge transfer devices for digital memory, analog delay, and image sensing. Short descriptions of different types of charge-coupled devices and MOS bucket-brigade devices are presented. Those factors such as transfer inefficiency, noise, and dark current which affect the performance of these devices in the above applications are discussed. Various possible organizations of charge transfer devices to serve different functions are described. Many charge transfer devices have been fabricated and already indicate a high degree of achievement. Transfer inefficiencies per transfer in the range 10−3 to 10−4 have been measured. Finally, it is projected that charge transfer devices will rapidly find their way into certain analog delay, image sensing, and digital applications.

A Model of Charge Transfer in Bucket Brigade and Charge-coupled Devices

Investigation of bucket brigade (BB) and charge-coupled devices (CCD) has resulted in the development of a general model for these devices and their various modes of operation. Similarities and differences between BB and CCD are discussed. The nonlinear partial differential equation of charge motion composed of self-induced drift, thermal diffusion, and electrode fringe-field terms is used to study CCD numerically. The factors that affect charge transfer are investigated by varying the stored charge density, the device length, the transfer-gate-to-storage electrode voltage, and the fringe field. The results include several plots of charge transfer vs time.

Charge Coupling; An All Electronic Approach to Position Sensitive Particle Detection

A review of the workings of charge coupled devices is given with the intention of bringing out the essential features and characteristics essential to understanding their capabilities and limitations as analog shift registers and imaging devices. While attention is focused on three phase devices, some attention is given to two and four phase devices as well as the bucket brigade devices. The special advantages of these devices as compared to existing imaging devices is discussed.