Stacked gate mid-channel injection flash EEPROM cell. I.Programming speed and efficiency versus device structure

Presents a new flash EEPROM cell which has been fabricated to achieve fast programming with low power. This memory cell attains speed and efficiency, comparable to the split-gate device, while preserving a simple stacked gate structure. The device programs faster than the stacked gate cell by a factor of about ten. Also, the threshold voltage shift of 5 V can be accomplished with the drain voltage of 3 V in about 50 μs. The proposed memory cell is strongly resistant against the punchthrough effect and is capable of erasure in byte unit at the drain side. Factors pertinent to programming are discussed, theoretically and experimentally, in correlation with device structures. The hot electron dwell time in the channel is shown to be an important parameter, affecting the programming speed and efficiency     

一种采用带-带隧穿热电子注入编程的新型快闪存贮器

提出一种采用带-带隧穿热电子注入编程的新型快闪存贮器结构,在便携式低功耗的code闪存中有着广泛的应用前景.该结构采用带-带隧穿热电子注入 (BBHE)进行"写"编程,采用源极Fowler-Nordheim隧穿机制进行擦除.研究显示控制栅编程电压为8V,漏极漏电流只有3μA/μm左右,注入系数为4×10-4,编程速度可达16μs,0.8μm存贮管的读电流可达60μA/μm.该新型结构具有高编程速度、低编程电压、低功耗、大读电流和高访问速度等优点.     

一种采用带-带隧穿热电子注入编程的新型快闪存贮器

提出一种采用带-带隧穿热电子注入编程的新型快闪存贮器结构,在便携式低功耗的code闪存中有着广泛的应用前景.该结构采用带-带隧穿热电子注入 (BBHE)进行"写"编程,采用源极Fowler-Nordheim隧穿机制进行擦除.研究显示控制栅编程电压为8V,漏极漏电流只有3μA/μm左右,注入系数为4×10-4,编程速度可达16μs,0.8μm存贮管的读电流可达60μA/μm.该新型结构具有高编程速度、低编程电压、低功耗、大读电流和高访问速度等优点.     

Drain disturb during CHISEL programming of NOR flash EEPROMs-physical mechanisms and impact of technological parameters

The origin of drain disturb in NOR Flash EEPROM cells under channel initiated secondary electron (CHISEL) programming operation is identified. A comparative study of drain disturb under channel hot electron (CHE) and CHISEL operation is performed as a function of drain bias and temperature on bitcells having different floating gate length and junction depth. The disturb mechanism is shown to originate from band-to-band tunneling under CHISEL operation, unlike that under CHE operation that originates from source-drain leakage. The effect of technological parameters (channel doping and drain junction depth) on CHISEL drain disturb is studied for both the charge gain (erased cell) and charge loss (programmed cell) disturb modes. Fullband Monte Carlo device simulations are used to explain the experimental results. It is shown that methods for improving CHISEL programming performance (higher channel doping and/or lower drain junction depth or halo) increase drain disturb, which has to be carefully considered for efficient design of scaled cells.     

Novel Single Polysilicon EEPROM Cell With Dual Work Function Floating Gate

A novel single polysilicon electrically erasable programmable read-only memory cell with dual work function floating-gate (DWFG) structure is presented in this letter. The floating gate of the proposed DWFG cell is doped with p+ on the source side and n+ on the drain side. For DWFG devices, the floating gate on the source side has a higher work function than that on the drain side. The work function difference and the intrinsic doped region at the middle of the floating-gate affect the channel potential distribution and generate a peak lateral electric field inside the channel, improving the channel's hot electron programming characteristics. The experimental results show that the proposed DWFG cell gives faster programming speeds and program operation at lower voltage than conventional cells     

DIBL considerations of extended drain structure for 0.1 μmMOSFET's

The drain-induced-barrier-lowering (DIBL) considerations of the extended drain structure were studied using two-dimensional (2-D) device simulations in the tenth-micrometer regime. We found that the drain extension length must be kept at a minimum in order to reduce the transistor cell area and to improve the device transconductance, G_m . However, without decreasing the deep source/drain junction depth, the minimum value of which is basically limited by the ability to form a good low resistive silicide contact, charge sharing associated with a small extension length deteriorates the short channel behavior of the device, via DIBL, even if aggressive scaling of the gate oxide thickness and the junction depth of the drain extension were used. The solution to this dilemma would be elevating the source/drain area by selective epitaxy to form a shallow, low resistive silicided junction. We propose here a novel device structure using the elevated silicide-as-a-diffusion-source (E-SADS), which improves the DIBL-G_m tradeoff, eliminates the contact problem, and maintains a minimal cell areal increase     

A simple EEPROM cell using twin polysilicon thin film transistors

A planar twin polysilicon thin film transistor (TFT) EEPROM cell fabricated with a simple low temperature (⩽600°C) process is demonstrated in this work. The gate electrodes of the two TFT's are connected to form the floating gate of the cell, while the source and drain of the larger TFT are connected to form the control gate. The cell is programmed and erased by Fowler-Nordheim tunneling. The threshold voltage of the cell can be shifted by as much as 8 V after programming. This new EEPROM cell can dramatically reduce the cost of production by reducing manufacturing complexity     

An Amorphous Silicon Local Interconnection (ASLI) CMOS with Self-Aligned Source/Drain and Its Electrical Characteristics

A CMOS device which has an extended heavily-doped amorphous silicon source/drain layer on the field oxide and an amorphous silicon local interconnection (ASLI) layer in the self-aligned source/drain region has been studied. The ASLI layer has some important roles of the local interconnections from the extended source/drain to the bulk source/drain and the path of the dopant diffusion sources to the bulk. The junction depth and the area of the source/drain can be controlled easily by the ASLI layer thickness. The device in this paper not only has very small area of source/drain junctions, but has very shallow junction depths than those of the conventional ones. The electrical characteristics of this device are as good as those of the conventional CMOS device. An operating speed, however, is enhanced significantly compared with the conventional ones, because the junction capacitance of the source/drain is reduced remarkably due to the very small area of source/drain junctions. For a 71-stage unloaded CMOS ring oscillator, 128 ps/gate has been obtained at power supply voltage of 3.3 V. Utilizing this proposed structure, a buried channel PMOS device for the deep submicron regime, known to be difficult to implement, can be fabricated easily.     

An asymmetrically doped buried-layer (ADB) structure forlow-voltage mixed analog-digital CMOS LSI's

A new CMOS structure has been developed that is distinguished by its asymmetrically doped buried layer (ADB). This structure makes it possible to achieve high drain output resistance and high transconductance necessary for high-performance analog circuits with a low-voltage power supply. The ADB structure has a high-impurity-concentration “pocket” layer near the channel edge of the buried layer only on the source side and a low-impurity surface region through the channel. The source-side channel region determines the threshold voltage and the drain-side channel region absorbs the drain potential. The low-impurity surface region reduces impurity scattering and enables high transconductance. The fabricated ADB CMOS structure increased the drain output resistance, transconductance, and saturation current down to a 0.3-μm channel length, as compared to a control structure. Furthermore, the drain junction capacitance was reduced because of the low impurity concentration beneath the drain region     

利用改进的电荷泵法研究SONOS存储器陷阱电荷的分布特性

在silicon-oxide-nitride-oxide-silicon(SONOS)等电荷俘获型不挥发存储器中,编程操作后注入电荷的分布会对器件的读取、擦写以及可靠性带来影响.利用电荷泵方法可以有效而准确地测量出注入电荷沿沟道方向的分布.为了提高测试精度,在进行电荷泵测试时,采用固定低电平与固定高电平相结合的方法,分别对SONOS器件源端和漏端进行注入电荷分布的测试.通过测试,最终获得SONOS存储器在沟道热电子注入编程后的电子分布.电子分布的峰值区域在漏端附近,分布宽度在50nm左右.     

Highly scalable ballistic injection AND-type (BiAND) flash memory

An AND-type split-gate Flash memory cell with a trench select gate and a buried n/sup +/ source is proposed. This cell, programmed by ballistic source side injection (BSSI), can provide high programming efficiency with a cell size of 5F/sup 2/. Furthermore, both the programming speed and the read current are enhanced by the shared select gate configuration.     

A new cell structure with a spread source/drain (SSD) MOSFET and acylindrical capacitor for 64-Mb DRAM's

A new cell structure for realizing a small memory cell size has been developed for 64-Mb dynamic RAMs (DRAMs). The source/drain regions of a switching transistor are raised by using a selective silicon growth technique. Because of lateral growth of the silicon over gate and field regions, the bitline contact can overlap the gate and field regions. The shallow source/drain junction by the raised source/drain structure realizes a reduction of gate length and isolation spacing. As a result, the DRAM memory cell area can be reduced to 37% of that using the conventional LDD MOSFET. In the fabrication of an experimental DRAM cell, a new stacked capacitor structure has been introduced to maintain enough storage capacitance, even in the small-cell area. The new capacitor is made by a simple and unique process using a cylindrical silicon-nitride sidewall layer. It has been verified that this cell structure has the potential to realize multimegabit DRAMs, such as 64-Mb DRAMs     

Characterization of programmed charge lateral distribution in a two-bit storage nitride flash memory cell by using a charge-pumping technique

In this paper, we use a modified charge pumping technique to characterize the programmed charge lateral distribution in a hot electron program/hot hole erase, two-bit storage nitride Flash memory cell. The stored charge distribution of each bit over the source/drain junctions can be profiled separately. Our result shows that the second programmed bit has a broader stored charge distribution than the first programmed bit. The reason is that a large channel field exists under the first programmed bit during the second bit programming. Such a large field accelerates channel electrons and causes earlier electron injection into the nitride. In addition, we find that programmed charges spread further into the channel as program/erase cycle number increases.     

Improved lifetime of poly-Si TFTs with a self-alignedgate-overlapped LDD structure

We investigated the lifetimes for various poly-Si thin film transistor (TFT) structures. A gate-overlapped lightly doped drain (GOLDD) structure was self-aligned by the side etching of Al-Nd in an Al-Nd/Mo gate electrode. The dopant activation process in the LDD regions of GOLDD TFTs was performed by using a H₂ ion-doping technique. We also observed the effect of lifetime on the source/drain activation process. The thermal annealing of the source/drain region was found to extend the lifetime. The predicted lifetime of our GOLDD poly-Si TFT is superior to those of non-lightly doped drain (non-LDD) and lightly-doped drain (LDD) poly-Si TFTs. The trapped-electron density at the drain junction after bias-stressing was also investigated using a two-dimensional (2-D) simulation     

A 600-volt MOSFET designed for low on-resistance

A 600-V vertical power MOSFET with low on-resistance is described. The low resistance is achieved by means of achieving near-ideal drain junction breakdown voltage and reduced drain spreading resistance from the use of an extended channel design. The various tradeoffs inherent in the design are discussed. Both calculated and experimental data are presented. The remote source configuration of the experimental device is also discussed.     

High Injection Efficiency and Low-Voltage Programming in a Dopant-Segregated Schottky Barrier (DSSB) FinFET SONOS for nor-type Flash Memory

A dopant-segregated Schottky barrier (DSSB) FinFET silicon–oxide–nitride–oxide–silicon (SONOS) for nor-type Flash memory is successfully demonstrated. Compared with a conventional FinFET SONOS device, the DSSB FinFET SONOS device exhibits high-speed programming at low voltage. The sharp dopant-segregated Schottky contact at the source side can generate hot electrons, and it can be used to provide high injection efficiency at low voltage without any constraint on the choice of the proper gate and drain voltage. The DSSB FinFET SONOS device is therefore a promising candidate for nor-type Flash memory with high-speed and low-power programming.      

Nonsilicide source/drain pixel for 0.25-μm CMOS image sensor

A nonsilicide source/drain pixel is proposed for high performance 0.25-μm CMOS image sensor. By using organic material spin coat and etch back, silicide is only formed on poly gate which can be used as interconnection, not for source/drain region that solve the optical opaqueness and undesirably large junction leakage of silicide. The performance of MOSFET changes little due to the high sheet resistance of nonsilicide source/drain. With H₂ annealing and double ion implanted source/drain junction, the dark current can be further reduced. The novel pixel (three transistors, 3.3 μm×3.3 μm, fill factor: 28%) shows low dark current (less than 0.5 fA per pixel at 25°C) and high photoresponse     

新型部分耗尽SOI器件体接触结构

提出了一种部分耗尽SOI MOSFET体接触结构,该方法利用局部SIMOX技术在晶体管的源、漏下方形成薄氧化层,采用源漏浅结扩散,形成体接触的侧面引出,适当加大了Si膜厚度来减小体引出电阻.利用ISE-TCAD三维器件模拟结果表明,该结构具有较小的体引出电阻和体寄生电容、体引出电阻随器件宽度的增加而减小、没有背栅效应.而且,该结构可以在不增加寄生电容为代价的前提下,通过适当的增加Si膜厚度的方法减小体引出电阻,从而更有效地抑制了浮体效应.     

The insulated gate tunnel junction triode

The gate modulated voltage breakdown of the drain diode in the MOS transistor is considered and shown to be direct electric field control of a reverse biased surfacep+-njunction. A structure designed to isolate this effect has been suggested by Atalla and experimentally evaluated by Nathanson, et al., and by the authors. The mechanism of operation discussed involves the application of an external electric field normal to the surface of the highly doped side of the junction to produce direct field emission of carriers. The reverse biased low doped side of the junction then acts as a collector of the field-emitted carriers resulting in a net current flow across the junction. Using the Atalla structure, a model is presented and a quantitative theory is developed to explain and predict the device performance. It is found that the actual device may be represented as an MOS transistor in series with an "ideal" field-controlled tunnel junction, and that the performance of the actual device can never be better than that of the limiting MOS transistor. The theoretical characteristics of the ideal field-controlled tunnel junction are derived and found to agree closely with the experimental results. It is shown that, at the present time, the device is limited by the "ideal" tunnel junction region and not by the series MOS transistor.     

SiGe source/drain structure for the suppression of theshort-channel effect of sub-0.1-μm p-channel MOSFETs

A bandgap engineering technique is proposed for the suppression of the short-channel effect (SCE) and its effectiveness is quantitatively calculated in the case of the SiGe source/drain structure with a device simulation. The drain-induced barrier lowering (DIBL) and the charge sharing are suppressed by the presence of the valence band discontinuity between the SiGe source/drain and Si channel. In order to obtain the full advantage of this structure, it is necessary to locate the SiGe layers both at the source/drain regions and the SiSe/Si interface at the pn junction or inside the channel region. The effectiveness increases with the increase of the valence band discontinuity (Ge concentration). As a result of the suppression of the SCE and the reduction of the minimum gate length, the drain current increases, and thus high-speed operation can be realized with this technique