2兆赫至60兆赫的温度补偿晶体振荡器

用在通信设备中产生稳定频率的晶体振荡器,它们对工作温度的频率稳定度△f/f=10~(-5)至10~(-6),这种稳定度基本上是由石英晶体本身决定的。对于那些需要较好稳定度的应用场合,都必须提供温度的稳定化或温度的补偿。与温度稳定的种种方案比较,温度补偿振荡器具有容积小,耗电少,检修方便,和价格低廉等优点。     

一种电流温度稳定度小于1μA/℃的V/I变换器

本文介绍一种高温度稳定度的V/I变换器电路,通过一种可以调节温度变化量的温度补偿电路,使V/I变换器的输出电流温度稳定度小于1μA/℃。应用于对电流稳定度要求极高的传感器信号处理或精密仪器仪表电路。     

简易铷原子频率源

在诸如单边带通讯及脉码调制等许多系统中,都需要有高精度频率源。应用晶体振荡器往往就能满足此精度要求。晶振具有极好的短期稳定度,但受到晶体固有老化的影响,长期稳定度较差。若保持晶振温度恒定,则稳定度可优于1×10~(-7)/每年。但这种     

温度补偿式晶体振荡器

在无线电通信设备和电子仪器中,广泛使用各种晶体振荡器。对于那些频率稳定度要求在10~(-7)～10~(-9)数量级作为频率基准应用的场合,都采用高稳定度晶体振荡器。它选用高精度石英谐振器,并置于恒温槽中。虽然它的稳定度很好,但由于电路复杂,功耗大,体积重量也比较大,而且需要较长的预热时间才能得到给定的频率稳定度,因此,应用受到一定限制。而温度补偿式晶体振荡器的体积小,省电,具有比普通晶体振荡器频率稳定度高以及接通电源无需预热时间就能达到预期的稳定度等优点,受到越来越多的重视。     

温补晶体振荡器的频率温度稳定度

大部分晶体振荡器生产厂家的数据手册不会兼顾所有使用者的需要,特别是温补晶体振荡器的频率温度稳定度指标,多数情况下,数据手册所列指标往往只适应于某一类典型的应用场合或只符合生产厂家与其某几个主要用户的验收规则,所以只有充分理解频率温度稳定度的不同定义方法、与频率温度稳定度相关的其他频率温度特性指标、不同的环境温度测试方法,才能正确制定符合自己使用要求的频率温度稳定度指标,不加分析地简单套用频率温度     

雪面上湍流谱特征研究

采用35 m铁塔上的超声风速仪数据,分析了雪面上近地层速度和温度谱,发现不同稳定度的湍流谱在高频时合并在一起,而低频谱并没有随稳定度呈现规律性变化,但随平均风速分开.给出了与稳定条件无关的雪面上湍流谱的拟合公式.并检验了雪面上局地各项同性假设.用归一化谱拟合谱幂率,拟合结果与-5/3的符合度高达85%.速度谱和温度谱惯性区谱幂率都集中分布在-5/3附近.惯性子区速度谱幂率与稳定度没有明显关系,温度谱中性时偏离比较大.     

光纤链路时延波动对频率传递稳定度的影响

为研究光纤频率传递的稳定度损失,分析了光纤链路时延波动对频率传递稳定度的影响,得出因温度变化引起的链路长度变化、折射率变化和激光器输出波长漂移带来的时延波动是影响频率传递稳定度的主要因素。建立Round-trip时序模型,定量分析时延波动残留,发现因环境温度缓变引入的时延波动可以得到有效补偿,因激光器动态结温度快变导致输出波长漂移引入的时延波动无法有效补偿,是稳定度损失的关键因素。降低激光器动态结温度的变化速率,是提高频率传递稳定度的有效手段。要使时延波动对频率传递稳定度的影响小于10~(-15)s~(-1)、10~(-20)d~(-1)(d~(-1)即每天),必须采取有效的温控措施,精确控制激光器动态结温度变化率,使其小于0.04℃/s。     

一款新型高频率稳定度ATCXO芯片的设计

基于0.35 μm CMOS工艺,采用全模拟电路设计实现了温度补偿晶体振荡器芯片(ATCXO).设计了新型三次函数发生器补偿电路,并利用E2 PROM记忆系统温度参数实现自动修调;为进一步提高输出频率稳定度,设计了振荡器电压稳定电路,消除电源电压的影响.仿真结果表明,在-40℃～+100℃宽温度范围内,工作电压为3.3...     

激光恒流源设计中的两个主要参数

本文提供了一种推导激光恒流源输出电阻和输出电流稳定度计算公式的方法,讨论了温度对输出电流稳定度的影响.     

怎样选择一款合适的晶体振荡器

本文介绍了一些足以表现出一个晶体振荡器性能高低的技术指标,了解这些指标的含义,将有助于通讯设计工程师顺利完成设计项目,同时也可以大大减少整机生产厂家的采购成本。 总频差:在规定的时间内,由于规定的工作和非工作参数全部组合而引起的晶体振荡器频率与给定标称频率的最大频差。 说明:总频差包括频率温度稳定度、频率温度准确度、频率老化率、频率电源电压稳定度和频率负载稳定度共同造成的最大频差。一般只在对短期频率稳定度关心,而对其他频率稳定度指标不严格要求的场合采     

变温LPCVD沉积氮化硅薄膜的均匀性优化

以低压化学气相沉积(LPCVD)热壁立式炉为实验平台,由二氯硅烷和氨通过LPCVD工艺合成氮化硅薄膜,利用降温成膜提高氮化硅薄膜的膜厚均匀度。基于气体碰撞理论建立了氮化硅薄膜沉积速率与反应气体浓度的关系式。分析比较了LPCVD炉内不同升温速率沉积氮化硅薄膜的表面性能。发现在变温沉积阶段,选择合适的降温速率是实现薄膜沉积过程中预设温度变化的关键。在保证各温度区平均膜厚和晶圆片之间膜厚均匀度基本不变的前提下,通过实验找到沉积阶段的最佳变温速率,将晶圆片内(WIW)均匀度优化到1%以下,比恒温沉积薄膜的均匀度提高了约70%。这将有助于设备工艺能力的提升,更好地适应IC芯片工艺关键尺寸的缩小趋势。     

Equipment modelling of CVD and etching

This paper presents results of equipment simulation giving applications of the fluid-dynamic solution to three commonly used reactors in the semiconductor industry — Tungsten CVD, Aluminum plasma etching, and Poly LPCVD. The results obtained include the determination of three-dimensional profiles for pressure, temperature, velocity, concentration of different chemical species, etch rates, deposition rates and uniformity over the wafer. This simulation technique is an important tool for equipment and process optimization by both the equipment suppliers and process engineers, because it allows a better visualization of the variables that control the process and allows a fast estimation of how changes on the process parameters or hardware configuration influence the results.     

LPVCD的原理与故障分析

文中介绍了CVD工艺的种类和特点。以LPVCD为例,介绍了其工艺的基本原理,以及设备的基本结构。根据多年的设备维护经验,分析了LPCVD设备的常见问题,提出了处理措施。最后,总结出了LPCVD设备的工艺维护方法。     

A novel approach to silicon gate CMOS device scaling

A new approach is reported for fabricating scaled Si-gate CMOS devices using medium temperature (?900° C) LPCVD deposited SiO₂ as the dielectric interlayer. The film can be deposited from 850 to 1000°C using a graded temperature profile and optimum pressure. A maximum of 100 wafers with 8% variation of thickness per run has been achieved using the process described in this paper. The medium-temperature LPCVD SiO₂ film exhibited step-coverage as good as the conventional low temperature PSG film. Since the new film requires no high temperature treatment, the convetional Si-gate CMOS diffusion process has been used to obtain the micron and submicron junction depths that are required to fabricate scaled CMOS devices. Such a processing approach, converting a 5–6 μm geometry CMOS process to a 3 μm geometry CMOS process, is described.     

A methodology for optimizing a constant temperature polysilicondeposition process

A three-step approach to characterizing a low pressure chemical vapor deposition (LPCVD) constant temperature polysilicon process is discussed. This approach optimizes an LPCVD polysilicon process for both film uniformity and particles. The first step is to design and construct a constant deposition temperature polysilicon furnace to provide the best system performance possible in terms of particle generation and improved film uniformity. The second step is to characterize a process in this newly constructed furnace for both film uniformity and particles by using an experimental design that incorporated an L₁₈ orthogonal array. The hydrogen chloride preclean flow prior to deposition plays a key role in both defect generation and film uniformity. Both capacitance-voltage techniques and secondary ion mass spectrometry are used to understand this role. The third step is to verify the recommended setting from the experimental design by processing confirmation runs. Results from the confirmation runs in the optimally constructed polysilicon furnace show that particles can be reduced by up to 66% and film uniformity can be improved by 29% over the current production process     

一种简单高效的复合温度控制系统

介绍了常用的温度控制方式,比较了ON/OFF控制和常规PID控制的优点与存在的不足。根据电热烘箱各加热阶段的不同要求,提出了采用分段式控制的复合温度控制方案,即在温度偏差较大时采用强制加热方式提高系统的动态响应速度,温度偏差接近设定值时自动切换到PID控制方式以增强系统的稳态性能。试验结果表明这种复合式温度控制方式是解决提高加热效率和保证温度稳定性这一矛盾体的有效手段。     

Process control system for VLSI fabrication

A modular framework for the implementation of process control in VLSI fabrication is described. The system integrates existing approaches to process control with new methodologies in order to achieve online optimization and control of unit processes with consideration of preceding and following process steps. The process control system is based on three core modules. The flexible recipe generator determines an initial operating point in response to a new product design. The run-by-run controller tunes the recipe between runs based on feedback from postprocess and in situ measurements. The real-time controller further modifies the equipment settings during a process step based on in situ measurements. The algorithmic bases of these modules are described. The flexible recipe generator was used to optimize the LPCVD (low-pressure chemical vapor deposition) of polysilicon. The run-by-run controller was used to locally optimize and control a simulation of the LPCVD of polysilicon     

Performance study of n-MOS natural transistor fabricated by low thermal budget process

Natural n-MOS transistor and MOS capacitor test structures have been fabricated by the low temperature process design for better control on device dimensions. Si-SiO₂ interface properties and performance of LPCVD gorwn polysilicon gate natural transistor has been studied through MOS C-V analysis and physical-electrical modeling. Transistor behavior at cryogenic temperatures has also been analysed through MOS C-V characteristics and one dimensional transport equations.     

适用于沉积工艺的真空技术

半导体生产中的薄膜沉积工艺通常对真空泵的要求很严格。在该工艺中高故障率和停机现象较为普遍。iH真空泵是特别为应付恶劣的薄膜工艺环境所设计。阐述了iH系列干泵在LPCVD氮化硅工艺应用中的成功表现。     

Simultaneous in situ measurement of film thickness and temperatureby using multiple wavelengths pyrometric interferometry (MWPI)

Film thickness and temperature are two of the most important quantities in semiconductor manufacturing. They play a fundamental role in many standard production techniques like chemical vapor deposition (CVD, LPCVD, PECVD), thermal oxidation and diffusion. They are especially important for more recently developed technologies like molecular beam epitaxy (MBE), metal organic MBE (MOMBE), metal organic CVD (MOCVD), chemical beam epitaxy (CBE), etc. In this paper, an optical in situ method for simultaneous film thickness and temperature measurements-named multiple wavelengths pyrometric interferometry (MWPI)-is introduced, which is capable of high resolution (up to 0.1 nm for thickness and 0.025 K for temperature) and for real time data evaluation. It can be used for process control as well as in situ quality inspection without time delay or additional handling mechanisms and is suitable for monitoring single films as well as multilayer structures. MWPI is insensitive to vibration, rotation and misalignment of the wafer. Due to its optical basis it is also insensitive to hostile environments like high temperature and/or chemical reactive gases