Design and optimization of BCCD in CMOS technology

This paper optimizes the buried channel charge-coupled device (BCCD) structure fabricated by complementary metal oxide semiconductor (CMOS) technology. The optimized BCCD has advantages of low noise, high integration and high image quality. The charge transfer process shows that interface traps, weak fringing fields and potential well between adjacent gates all cause the decrease of charge transfer efficiency (CTE). CTE and well capacity are simulated with different operating voltages and gap sizes. CTE can achieve 99.999% and the well capacity reaches up to 25 000 electrons for the gap size of 130 nm and the maximum operating voltage of 3 V.     

A new configuration of CCD imager with a very low smear level—FIT-CCD imager

A new configuration of CCD imager has been developed to improve smearing. This new sensor introduces a storage region, which consists of pairs of vertical BCCD registers, between an interline transfer CCD imaging region and a readout horizontal CCD register. The configuration and operation of the new device (FIT-CCD imaging device) are described, together with the experimental results for 402(H) times 500(V) element imaging devices. The smear level observed is low as ∼0.45 percent at 50 times the saturation exposure, being the lowest level so far obtained in solid-state imagers. Degradation in the contrast transfer function due to introduction of the storage region is very little because of the minimized vertical transfer loss by the storage region configuration with pairs of half-long BCCD registers.     

A new accelerated transfer method for the CPD image sensor

A new charge transfer method for the CPD image sensor is proposed. In this method a high transfer speed is achieved with the use of an accelerated charge priming transfer (CPT) coupler, which consists of the array of the conventional CPT's and inverter amplifiers. This constitution strikingly increases the speed as well as the efficiency of the charge transfer from the vertical transport lines with large capacitance to the horizontal buried-channel charge-coupled (BCCD) shift register. Under a high transfer efficiency of more than 98 percent, a short transfer time less than 1 µs has been attained, independently of the signal charge magnitude.     

Experimental demonstration of a buried-channel charge-coupleddevice in 6H silicon carbide

Fundamental operation of the first buried-channel charge-coupled device (BCCD) in 6H-SiC is presented. The n-type buried-channel was formed by ion implantation of nitrogen, and a double level overlapping-polysilicon-gate process was adapted to the SiC MOS system. An electron mobility of 200 cm²/Vs was measured in the channel, which is doped 1.6×10¹⁷ cm^-3. An eight-stage, four-phase BCCD shift register was operated in the pseudo-two-phase configuration at room temperature. At 5.5 kHz, the charge transfer efficiency is greater than 99.4%     

A two-dimensional numerical approach to achieve a silicon BCCD celloptimal design

The single charge stored in a silicon buried-channel charge-coupled device (BCCD) is studied under different technological specification. The approach is to seek an accurate determination of this parameter by using a 2-D numerical device analysis program. The calculated data are compared to experimentally measured BCCD characteristics. These investigations have led to some trends for design optimization for designers whose main motivation is the scaling down of BCCDs     

A comparison of static bulk-channel charge-coupled device characteristics using uniform,Gaussian and measured impurity distributions

A comparison of the static characteristics of both three and two-phase bulk-channel CCDs with uniform, Gaussian and measured impurity distributions is presented. The characteristics are determined by using a simple one-dimensional model based upon the depletion approximation. It is shown that for phosphorus implantations that are subjected to high temperature oxidation/drive-in schedules, the resulting impurity distribution and BCCD characteristics are closer to those of the ideal uniform profile rather than the more commonly assumed Gaussian distribution.The analysis indicates that if a Gaussian impurity distribution is assumed significant errors in predicted BCCD characteristics result. For example, errors in excess of 20% occur in the calculation of the gate voltage required to hold the maximum signal charge for bulk-channel operation, and of 50% in the bulk-channel/interface potential. In the case of three-phase devices it is shown that approximation of the impurity distribution to a uniform profile gives sufficiently accurate results for most applications. However, for two-phase stepped oxide structures analysis indicates that optimisation of the maximum charge carrying capacity, whilst maintaining bulk-channel operation, can only be achieved if device operation is analysed using the measured impurity distribution.     

三沟道BCCD在X光区光电特性的数值模拟

本文对三沟道体电荷耦合器件（BCCD）在X光区的光电特性进行了数值模拟,结果表明：磁对X光的吸收曲线了硅制的三沟道BCCD不能在XI我区实现多光谱成像,通过理论分析,指出了能保证BCCD在X光区工作的衬底材料所应满足的吸收曲线,利用这种新材料制成的三沟道BCCD,其光敏特性可以分别在1．8keV,1.2keV,0.6keV处出现最大值。     

埋沟CCD器件电荷处理容量的二维数值模拟

借助于二维器件模拟软件PISCES-IIB,通过在某相CCD电极下的耗尽区注入数量可控的电子电荷,对埋沟CCD器件电荷容量进行了定量分析。采用此方法对一种沟道宽度为7μm的CCD信道电荷容量进行了瞬态模拟,对不同结深、不同沟道掺杂浓度对CCD电荷容量的影响进行了讨论。得到了此结构工艺参数的初步优化结果,即CCD沟道表面掺杂浓度为结深为1 μm时,埋沟CCD的电荷容量可达文章提出的方法适用于其他CCD单元结构电荷容量的模拟。     

Modeling of charge transfer by surface acoustic waves in a monolithic metal/ZnO/SiO2/Si system

This paper discusses modeling of minority-carrier charge transfer by surface acoustic waves (SAW's). An idealized, structure independent model which includes the mechanism of carrier diffusion is described and definitions of charge-transfer efficiency and charge capacity analogous to those of a conventional charge-coupled device are introduced and developed. The model is used to predict the fundamental upper limit performance of the device in the absence of surface-state trapping and bulk recombination generation. The parameters of the model are evaluated for the monolithic metal/ZnO/SiO2/Si system, and the model is used to predict charge distributions and charge capacity for surface wave frequencies in the range of 40 MHz to 2 GHz. At high frequencies, the predicted device performance is found to be limited by carrier diffusion and the SiO2thickness.     

Charge capacity analysis of the charge-coupled RAM cell

The charge (or storage) capacity of the dynamic charge-coupled (CC) random access memory (RAM) cell is analyzed. Theoretical expressions for the capacity are developed which provide excellent agreement between theory and experiment. Test devices were operated with typical dynamic metal-oxide-semiconductor (MOS) RAM voltages, and exhibited charge capacities (per unit area) up to 52 and 86 percent of that of the conventional one-transistor cell for substrate bias voltages of -5 and -1 V, respectively. A simplified model of the CC RAM cell is used to illustrate the dependence of the charge capacity on the device and operating parameters. This model is useful for defining the limitations on capacity and for comparing the capacities of the CC and the one-transistor cells for a variety of conditions. In general, the CC RAM cell charge capacity per unit area ranges from 50 to over 100 percent of that of the one-transistor cell for conventional device parameters. A somewhat higher range applies for projection to low-voltage and very high-density RAM's.     

A new extension method of retention time for memory cell on dynamic random access memory

Demands have been placed on dynamic random access memory (DRAM) to not only increase memory capacity and data transfer speed but also to reduce operating and standby currents. When a system uses DRAM, the restricted data retention time necessitates a refresh operation because each bit of the DRAM is stored as an amount of electrical charge in a storage capacitor. Power consumption for the refresh operation increases in proportion to memory capacity. A new method is proposed to reduce the refresh power consumption dynamically, when full memory capacity is not required, by effectively extending the memory cell retention time. Conversion from 1 cell/bit to 2^N cells/bit reduces the variation of retention times among memory cells. The proposed method reduces the frequency of disturbance and power consumption by two orders of magnitude. Furthermore, the conversion itself can be realized very simply from the structure of the DRAM array circuit, while maintaining all conventional functions and operations in the full array access mode.     

Organic Field Effect Transistors Based on Graphene and Hexagonal Boron Nitride Heterostructures

Enhancing the device performance of single crystal organic field effect transistors (OFETs) requires both optimized engineering of efficient injection of the carriers through the contact and improvement of the dielectric interface for reduction of traps and scattering centers. Since the accumulation and flow of charge carriers in operating organic FETs takes place in the first few layers of the semiconductor next to the dielectric, the mobility can be easily degraded by surface roughness, charge traps, and foreign molecules at the interface. Here, a novel structure for high‐performance rubrene OFETs is demonstrated that uses graphene and hexagonal boron nitride (hBN) as the contacting electrodes and gate dielectric layer, respectively. These hetero‐stacked OFETs are fabricated by lithography‐free dry‐transfer method that allows the transfer of graphene and hBN on top of an organic single crystal, forming atomically sharp interfaces and efficient charge carrier‐injection electrodes without damage or contamination. The resulting heterostructured OFETs exhibit both high mobility and low operating gate voltage, opening up new strategy to make high‐performance OFETs and great potential for flexible electronics.     

Barrier lowering in short-channel CCD's

In a two-phase overlapping CCD structure, the potential barrier height in the gap between the two storage gates decreases as the gap length is reduced due to fringing field effects. The barrier lowering limits the charge handling capacity in short-channel CCD's. A two-dimensional model is developed to calculate the barrier height for the various gap lengths. A simple measurement technique is developed to obtain experimental data using submicrometer structures and the data is compared with the model. Several important process parameters relating to the barrier lowering are investigated for design consideration.     

Redox-Active Polymer Integrated with MXene for Ultra-Stable and Fast Aqueous Proton Storage

Proton is a charge carrier with the smallest ionic size and quickest kinetics, making aqueous proton batteries (APBs), a promising technology for safe and profitable energy storage systems. Despite being potential electrode materials, organic compounds have not yet been fully investigated in terms of proton storage properties and APB applications due to their low capacity and unstable cycle life in aqueous electrolytes. Herein, a novel redox-active polymer (PDPZ) with diquinoxalino-phenazine as the structural unit has been designed, which is further integrated with MXene nanosheets to construct a flexible PDPZ@MXene electrode material with a rapid and ultra-stable proton storage behavior. In-operando monitoring techniques, i.e., in situ Raman and in situ FTIR, demonstrate the highly reversible redox reaction between CN and C N/N H bonds in electro-active PDPZ molecule with the strong proton absorption ability. Theoretical calculation further proves the electron transfer from MXene to PDPZ promotes the redox reaction of the PDPZ@MXene electrode. As a result, a flexible APB device is developed with a considerable energy density (64.3 mWh cm⁻³), a supercapacitor-level power density (6000 mW cm⁻³), and a record lifespan with ≈98.2% capacity retention over 10 000 cycles, revealing its potential applications in satisfying the various requirements of energy storage systems.     

Charge handling capacity in charge coupled devices

In analog signal processing applications, the charge handling capacity of a charge coupled device (CCD) is an important parameter that determines the dynamic range. In this paper, approximate expressions for the signal handling capacity for surface-channel and buried-channel CCD's are derived and compared. The upper limit for the buried-channel charge capacity is imposed by the onset of surface electron accumulation.     

Introduction to charge-coupled devices

The operating principles of charge-coupled devices are described in terms of the basic properties of semiconductors. The overall aim is for those unfamiliar with CCD's to understand how they work and thus to appreciate their capabilities as well as their limitations. The topics discussed include charge storage and transfer, electrical and optical inputting of charge and charge sensing, factors governing maximum and minimum operating frequencies, transfer efficiency, and basic CCD fabrication techniques.     

Metal Oxide/Graphene/Metal Sandwich Structure for Efficient Photoelectrochemical Water Oxidation

Single-layer graphene (SLG) has drawn considerable interest in photoelectrochemical (PEC) cells due to its atomically flat pinhole-free structure and remarkable in-plane carrier mobility. It is challenging, however, to obtain efficient SLG-modified photoelectrodes for PEC water splitting mainly due to the inefficient charge transfer interface. Here, a transition metal oxide/SLG/transition metal sandwich structure modified n-Si-based model photoanode is constructed to regulate the interfacial charge transfer behavior for enhanced PEC water oxidation performance. In this sandwich configuration, SLG tailors the morphology, structure, and work function properties of surface metal electrocatalysts to obtain both higher thermodynamic photovoltage and faster kinetical charge transfer at the semiconductor/electrolyte interface. In addition, SLG promotes the surface catalytic reaction as an effective charge trap and storage layer. This study provides a new structural design to engineer the SLG interfacial properties for high-performance energy conversion devices.     

载流子扩散对电荷耦合器件调制传递函数的影响

以表面沟道前射电荷耦合器件(CCD)为例,从理论上讨论了CCD内载流子扩散的机制,提出了利用光积分周期内收集的总信号电荷密度求CCD调制传递函数的方法,并获得了耗尽宽度随信号电荷密度改变时的CCD调制传递函数曲线,讨论了载流子扩散对传递函数的影响.利用已有的传递函数测量仪进行实验,数值模拟结果与实验结果基本吻合.     

On the design of ion implanted buried channel charge coupled devices (BCCDs)

The allowable range for the channel dose of a buried channel CCD is obtained. The maximum charge handling capacity without surface trapping effect is found to depend on the channel dose and the substrate concentration. In the case of two phase buried channel CCDs, the barrier implant dose can be estimated depending on the charge storage capacity desired. The result is applicable to ion implanted shallow junction devices and can be extended to deeper junction epitaxial buried channel devices.     

Operating principles and performance of a novel a-Si:H p-i-n-based X-ray detector for medical image applications

This work develops a novel hydrogenated amorphous silicon (a-Si:H) p-i-n photodiode-based X-ray detector aimed at medical image applications. The new detector consists of an a-Si:H p-i-n photodiode and a stacked dielectric layer, deposited on the p-layer (n-i-p-SiN/sub x/) or the n-layer (p-i-n-SiN/sub x/) of the p-i-n photodiode, as the main charge storage element. This detector operates as a capacitor and is connected in parallel to a reverse-biased p-i-n photodiode during the detection cycle to accumulate photon-converted charges. The junction capacitance (C/sub j/) of the p-i-n diode was enhanced by this stacked dielectric layer without reducing the active area of the detector. The design of the charge storage capacity and the photon-charge transfer efficiency can be optimized separately for various applications. Moreover, the linearity, dynamic range of operation, and data retention capacity of the detector were found to be markedly improved by the enlarged capacitance in the detector. The operating principles and performance of this novel device are discussed, and the corresponding control sequence of the switch of the device array is also addressed. The experimental results proved that this novel structure is valid and can be applied to construct effectively a two-dimensional detection array, offering considerable advantages of the novel device in X-ray medical image applications.