外文翻譯--10Gbs的高性能PIN和APD光接收器

1、high performance 10 gb/s pin and apd optical receiversabstract the increasing market demand for high-speed optical- transmission systems at rates of 10 gb/s has resulted in technical challenges for suppliers of high-performance, manufacturable opto-electronic components and systems. in particular, t

2、he performance of the inp semiconductor devices, integrated circuits (ics) and hybrid ic modules strongly influences the achievable transmission capability.an optical receiver design is presented which incorporates an inp-based p-i-n (positive-intrinsic-negative) photodetecto(pd) or avalanche photod

3、etector (apd) and a gaas high electron mobility transistor (hemt) pre-amplifier integrated circuit. several aspects of the receiver design are presented, including the p-i-n pd and apd structures and performance, pre-amplifier performance, hybrid module layout and electrical simulation and results.

4、the use of analytical techniques and theory commonly used in the design of microwave amplifiers and circuits is emphasized. receiver test results are included which are in close agreement with predicted theoretical performance.introduction over the past 15 years the demand has continued to increase

5、for higher speed and higher performing opto- electronic components. components designed to operate at data rates of 155 mb/s through 1 gb/s are now used in high volume, are manufactured with high yields, and are available from several suppliers. components designed for 2.5 gb/s are fast approaching

6、this manufacturing status as well. the emphasis now for new opto-electronic product development centers around performance requirements at transmission rates of 10 gb/s and higher.the optical receiver represents one of the key components in optical-fiber based communication systems, and is generally

7、 considered as a component, or module, which is available with specified levels of electrical functionality or integration. the basic elements of an optical receiver module are a photodetector, pre-amplifier, limiting or agc(automatic gain control) amplifier, and clock and data recovery circuitry. a

8、t data rates of 2.5 gb/s and below, the system designer can currently purchase the optical receiver elements in various levels of integration, from a discrete photodetector module to a fully integrated clock and data recovery module.in many multi-element systems and circuits the performance is stron

9、gly influenced by those elements which are located near the input of the system or circuit. this is certainly true in a digital optical receiver where the performance of the photodetector and pre-amplifier elements will have a strong impact on receiver and system performance. in addition to the indi

10、vidual performance of these two elements, the electrical and physical design of the interface between them is equally critical. at speeds of 10 gb/s, the current focus for suppliers of optical receivers is the development of modules, which incorporate the photodetector and pre-amplifier elements. na

11、turally as time progresses, the additional electrical functions will be incorporated into the modules as well. this paper focuses on the design and characterization of 10 gb/s optical receiver modules that incorporate the photodetector and pre-amplifier elements.optical receiver basics before consid

12、ering 10 gb/s receiver design a brief review is presented of optical receivers for digital applications. a basic schematic of an optical receiver front-end is shown in figure i. the schematic includes the photodetector and pre- amplifier elements.the key perfomance requirements of an optical receive

13、r are high sensitivity, wide dynamic range and adequate bandwidth for the intended application. the purpose of the pd is to convert the incident optical signal to an electrical current. the photodiode should have the following performance characteristics: high responsivity (quantum efficiency), low

14、dark current, low capacitance and wide bandwidth. for applications at optical wavelengths of 1310nm and 1550 nm, high quantum efficiency ingaas / inp type photodetectors are commonly selected. the purpose of the pre-amplifier is to convert the photocurrent from the pd into a usable voltage that can

15、be further processed. the common pre-amplifier technology used in optical receivers is transimpedance amplification, (tia) due to its optimum trade-off between noise, dynamic range and bandwidth. other types of pre-amplifiers include high-impedance and low-impedance (e.g. 50) designs.p-i-n photodete

16、ctorsour p-i-n photodiode is a double-heterojunction structure grown on an n+-inp substrate and consists of an n+ -1np buffer layer, an n-ingaas active layer, and an n inp cap layer. the buffer growth precedes the active layer growth to provide a surface with fewer defects than exist on the bare sub

17、strate surface. the in0.53ga0 .47as active layer is lattice-matched to inp and, with a bandgap g 0.75 ev, is sensitive to light with wavelengths shorter than 1.65 m. the device exhibits a short-wavelength cutoff at 0.90m since more energetic short-wavelength light is absorbed in the inp (g 1.35 ev)

18、before it reaches the ingaas. the larger-bandgap inp cap layer reduces surface leakage (relative to ingaas) and is passivated using si3n4. using etched patterns in the si3n4 as a mask, high-reliability planar diodes are created by diffusing a p-type dopant (zn) to form one-sided p+-n- junctions just

19、 below the inp-ingaas (cap-active) heterojunction (see fig. 5a). contact metallization alloyed to the diffused junction allows electrical contact to the p-side of the junction. after thinning the substrate to 120 m, the back side of the wafer is metallized to provide electrical connection to the n-s

20、ide of the junction. apertures in the backside metallization allow optical coupling to the active region in a back-illuminated geometry, and an anti-reflecting (ar) si3n4 coating is present in the aperture to eliminate reflection from the air-inp interface.several of the critical device characterist

21、ics pose conflicting design constraints that must be optimized for good high frequency performance. of primary importance is the ability to achieve sufficient 3-db bandwidth. the standard p- i-n diode has two fundamental bandwidth limitations: (i) finite carrier transit time and (ii) rc roll-off. th

22、e finite transit time taken by photon-induced carriers to traverse the active region can be shortened by reducing the thickness of the active region, but only at the expense of increased capacitance per unit area and lower quantum efficiency (which results in lower responsivity). the tendency toward

23、s increased capacitance for thinner active layers can be offset by reducing the total junction area, but this leads to greater difficulties in achieving high optical coupling efficiency and reliable electrical connections (e.g., by wire bonding).for 10 gb/s performance, the conflicting requirements

24、just described can be adequately resolved using a device diameter of 30 um. in this case, an active layer width wa 2.3 um gives rise to average transit times of about 25 ps implying a maximum bandwidth f3-db 18 ghz. the resulting capacitance of 0.15 pf contributes a bandwidth limitation of f3-db 21

25、ghz assuming a 50load. (note that low contact resistance is yet another device requirement necessary for minimizing rc bandwidth limitations.) direct measurement of a wire-bonded photodiode using microwave probes has confirmed a device bandwidth of 20 ghz. finally, assuming an ar coating reduces sur

26、face reflections to negligible levels, the quantum efficiency, of such a device is still reasonably high:= l - exp(-wa) 80% where the absorption coefficient 0.70 um-1 for n- -ingaas and a wavelength of 1.55 um. avalanche photodetectorsthe design of an avalanche photodiode for use at 10 gb/s is consi

27、derably more difficult than for a p-i-n diode, but the benefits to receiver sensitivity can be substantial. the utility of the apd is that it provides a means of circumventing the basic quantum limitation of the p-i-n diode, which dictates that each photon can generate only a single electron-hole pa

28、ir. the apd structure is designed to create a region of electric field sufficiently high that a single carrier is accelerated enough to generate additional electron-hole pairs through impact ionization. newly generated carriers are similarly accelerated, and so a single carrier can trigger an avalan

29、che effect, which provides internal gain resulting in many electron-hole pairs generated per absorbed photon. all ingaas-inp apds employ a separate absorption and multiplication (sam) structure (see fig. 2b) since high fields in the ingaas absorption region would induce large tunneling currents befo

30、re the onset of the avalanche effect. the low- doped ingaas absorption and inp multiplication regions are spatially separated by a layer of n-doped inp used to maintain low field in the ingaas and high field in the inp. the inp multiplication region is terminated by a p+-n- junction in inp created b

31、y a diffusion technique similar to that used in fabricating p-i-n diodes. the polarity of the device is determined by the fact that holes have a higher probability than electrons for ionizing collisions in inp; therefore, the structure is designed to inject photoexcited holes from the ingaas into th

32、e inp multiplication region to seed the avalanche process. although there is noise inherent in the avalanche effect (due to stochastic fluctuations in the number of carriers generated per photon), as long as this avalanche noise is no greater than the noise from other components in the receiver (suc

33、h as amplifiers), the apd can provide a significant increase in the receiver signal-to-noise ratio. this is particularly attractive at higher frequencies at which increased amplifier noise is unavoidable.apd design is complicated by a number of factors. foremost among these is the difficulty in cont

34、rolling premature avalanche breakdown at the edge of the device.the geometry of planar diffused junctions includes inherent curvature at the junction periphery. this curvature typically causes locally enhanced electric fields, and the consequent enhanced avalanche at the junction periphery leads to

35、an undesirable non-uniformity in the multiplication profile across the device. to solve this problem, we have used a novel double-diffusion technique to shape the diffusion profile so that edge fields are reduced.achieving high bandwidth apd performance involves the same transit time and rc limitati

36、ons described for the p-i-n diode. however, there is an additional bandwidth constraint imposed by the avalanche process itself in the form of a fixed gain-bandwidth (g-bw) product. the carrier acceleration and impact ionization involved in creating avalanche gain require an avalanche build-up time

37、proportional to the gain, so the higher the operating gain is, the lower will be the device bandwidth. (note that another new bandwidth- limiting process is introduced since all electrons created in the multiplication layer during the avalanche process must traverse the ingaas absorption region to r

38、each the n-contact.) higher g-bw products result when thinner, higher-field multiplication regions are used. with a multiplication layer thickness of -0.2 m, we have achieved g-bw products of about 90 ghz (see fig. 3).a very attractive attribute of our apd design is the fact that it is based on well

39、-established processes identical to those used in fabricating planar p-i-n diodes. this can be expected to result in favorable production yields and extremely high- reliability devices. we have confirmed that our 2.5 gb/s apds (based on a structure similar to that described above for the 10 gb/s dev

40、ice) have reliability performance comparable to p-i-n diodes, and initial lifetesting on our 10 gb/s apds has provided similar results. conclusionsthe design of manufacturable optical receiver modules has been presented for 10 gb/s applications. both a p-i-n or apd detector can be used, depending on

41、 sensitivity requirements. the design and fabrication of the planar ingaas-inp photodetectors was presented along with a physical description of the optical module. a detailed electrical analysis based on microwave cad simulation was presented with an emphasis on the identification of the critical c

42、ircuit elements that effect the microwave performance. finally, prototype p-i-n and apd receiver test results were presented and compared to the simulated results, showing a relatively strong correlation. 作者：jim rue, mark mer, nitish agrawal, stephen bay and william sherry國(guó)籍：美國(guó)出處：electronic componen

43、ts and technology conference，1999. 10gb/s的高性能pin和apd光接收器摘要隨著市場(chǎng)需求對(duì)傳輸速率為10gb/s的高速光纖系統(tǒng)日益增長(zhǎng)，使之對(duì)生產(chǎn)高性能，制造光電元件和系統(tǒng)的供應(yīng)商的提出了更高的技術(shù)要求。特別是inp半導(dǎo)體器件，集成電路（ic）電路和混合ic模塊的性能，對(duì)實(shí)現(xiàn)傳輸能力有著的強(qiáng)烈影響。在一種光接收機(jī)的設(shè)計(jì)上，人們提出結(jié)合采用基于inp基腳的p-i-n結(jié)光電探測(cè)器或雪崩光電探測(cè)器（apd）和砷化鎵高電子遷移率晶體管（hemt）的前置放大器集成電路。光接受器的設(shè)計(jì)，包括在p-i-n結(jié)光電探測(cè)器和apd的結(jié)構(gòu)和性能，前置放大器性能，混合動(dòng)力模塊布

44、局和電氣模擬結(jié)果的幾個(gè)方面的設(shè)計(jì)。經(jīng)常強(qiáng)調(diào)在微波放大器及電路設(shè)計(jì)中使用的分析技術(shù)和理論。使接收器的測(cè)試結(jié)果與預(yù)測(cè)的理論性能接近一致。引言在過(guò)去15年中，人們對(duì)于速度更高和性能更高的光電組件的需求一直在不斷增加。設(shè)計(jì)出來(lái)的數(shù)據(jù)傳輸速率為155mb/s與1gb/s的光電組件現(xiàn)在正在在被大批量使用，并且其容易生產(chǎn)且產(chǎn)量高，容易從幾個(gè)供應(yīng)商中得到。設(shè)計(jì)的傳輸速率為2.5千兆/秒的光電組件的生產(chǎn)同樣快速達(dá)到了這個(gè)狀況?，F(xiàn)在光電產(chǎn)品研發(fā)中心新的重點(diǎn)是研發(fā)傳輸速率性能要求約為10gb/s和更高的元件。光接收器是基于光纖通信系統(tǒng)的關(guān)鍵部件之一，一般被認(rèn)為這是裝備在指定的電氣功能或一體化水平設(shè)備的組件或模塊。光

45、接收器模塊的基本元件是光探測(cè)器，前置放大器，限制或agc（自動(dòng)增益控制）放大器，時(shí)鐘和數(shù)據(jù)恢復(fù)電路。如果從一個(gè)離散探測(cè)器模塊到完全集成的時(shí)鐘和數(shù)據(jù)恢復(fù)模塊的數(shù)據(jù)傳輸速率要求在2.5gb/s及以下的，系統(tǒng)設(shè)計(jì)師目前可以購(gòu)買在各種水平的集成光接收機(jī)的基本元件。 在許多元件系統(tǒng)和電路的性能受到那些位于附近的輸入系統(tǒng)或電路的元件的強(qiáng)烈影響。這是確實(shí)存在的，在數(shù)字光接收機(jī)上的光電探測(cè)器和前置放大器元件的性能將會(huì)對(duì)接收器和系統(tǒng)性能產(chǎn)生強(qiáng)烈影響。除了這兩種元件的獨(dú)特影響外，它們之間的接口的電氣和物理設(shè)計(jì)也是同樣重要。在傳輸速度為10gb/s的基礎(chǔ)上，光接收器供應(yīng)商目前開(kāi)發(fā)的重點(diǎn)是發(fā)展結(jié)合光探測(cè)器和前置放大器

46、元件的模塊。自然隨著時(shí)間的推移，更多的電氣功能同樣也將被納入該模塊。本文重點(diǎn)是描述和設(shè)計(jì)結(jié)合光探測(cè)器和前置放大器的傳輸速率為10gb/s的光接收模塊研究。光學(xué)接收器的基礎(chǔ)在考慮10gb/s接收器設(shè)計(jì)的之前,簡(jiǎn)要回顧以前提出的數(shù)字化應(yīng)用中的光接收器。光接收器前端的一個(gè)基本原理如圖1所示，示意圖包括光探測(cè)器和前置放大器的元件。圖1 光接收器前端的一個(gè)基本原理圖光接收器的關(guān)鍵要求是在實(shí)際應(yīng)用中要有很高的靈敏度，寬動(dòng)態(tài)范圍和足夠的頻寬。光電二極管（pd）的目的是將入射的光信號(hào)轉(zhuǎn)換成電流。光電二極管應(yīng)該具有以下性能特點(diǎn)：高響應(yīng)（量子效率），低暗電流，低電容和寬頻帶。對(duì)于應(yīng)用在1310nm和1550nm波

47、長(zhǎng)的光的波長(zhǎng)，量子效率高的ingaas / inp的類型探測(cè)器是常用的選擇。前置放大電路的目的是把從光電二極管（pd）的光電流轉(zhuǎn)換成可用的電壓，從而能進(jìn)一步操作。由于對(duì)噪聲、動(dòng)態(tài)范圍和頻寬之間的最佳權(quán)衡，常見(jiàn)的用于光接收器前置放大電路具有高阻抗。其他類型的前置放大器，包括高阻抗和低阻抗（例如50）的設(shè)計(jì)。pin光電探測(cè)器我們的pin光電二極管是以一個(gè)n+-inp為襯底的雙異質(zhì)結(jié)結(jié)構(gòu)和一個(gè)n+-inp緩沖層，一個(gè)n-ingaas積極層和n型inp的帽層。在積極層增長(zhǎng)之前，緩沖區(qū)增長(zhǎng)提供的表面比存在的裸露材料表面缺陷少。in0.53ga0 0.47活性層匹配的電勢(shì)差為0.75 ev的能隙的inp晶

48、格，對(duì)波長(zhǎng)小于1.65微米的光很敏感。該器件在遇到0.90m波長(zhǎng)以下的光時(shí)才截止接收，因?yàn)楦谢盍Φ亩痰牟ㄩL(zhǎng)的光在到達(dá)ingaas之前被inp（電勢(shì)1.35 ev）吸收。較大能隙的inp帽層可減少表面泄漏電流（相對(duì)的ingaas），并使用鈍化si3n4 。使用口罩的si3n4的蝕刻模式，用摻雜（鋅）的擴(kuò)散p型去形成片面的p-n結(jié)創(chuàng)造的可靠性高的平面二極管在inp-gaas（帽活躍）異質(zhì)結(jié)的正下方（見(jiàn)圖2a）。使金屬合金與擴(kuò)散結(jié)連接，以便允許電跟結(jié)區(qū)的p端接通。在把襯底減薄到120微米后，薄片的背后的金屬是用來(lái)提供電氣與n端連接的。背面金屬上的光圈允許光耦合到處在被光的活躍的幾何區(qū)，在光圈中的防

49、反射（ar）si3n4涂層是來(lái)消除來(lái)自air-inp接口的反射。設(shè)計(jì)時(shí)一些關(guān)鍵設(shè)備造成的沖突必須得到約束，并得到優(yōu)化從而具有為良好的高頻性能。最重要的是能夠?qū)崿F(xiàn)足夠的3db帶寬。標(biāo)準(zhǔn)pin二極管有兩個(gè)基本的帶寬限制：（1）有限的渡越時(shí)間；（2）信號(hào)衰減。只有在增加單位面積電容和較低的量子效率（導(dǎo)致響應(yīng)較低）的費(fèi)用時(shí)，才可以通過(guò)縮短減少厚度活躍的地區(qū)來(lái)減少光子傳輸?shù)交钴S地區(qū)的時(shí)間。對(duì)減薄活性層而靠電容增加的趨勢(shì)，可以通過(guò)降低總交界處被來(lái)抵消，但是這將使實(shí)現(xiàn)高光耦合效率和可靠的電氣連接（例如，焊線）具有更大的困難。為實(shí)現(xiàn)10gb/s的性能，并解決描述的相互矛盾，只要使用直徑30微米的設(shè)備就行了。在這種情況下，有源層寬度2.3 um 的wa產(chǎn)生的平均運(yùn)輸時(shí)間約25ps，這就意味最大帶寬（f3-db ）為18ghz 。假定有50負(fù)載