Monolithic integration of an infrared photon detector with a MEMS-based tunable filter

The monolithic integration of a low-temperature microelectromechanical system (MEMS) and HgCdTe infrared detector technology has been implemented and characterized. The MEMS-based tunable optical filter, integrated with an infrared detector, selects narrow wavelength bands in the range from 1.6 to 2.5 /spl mu/m within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The entire fabrication process is compatible with two-dimensional infrared focal plane array technology. The fabricated device consists of an HgCdTe SWIR photoconductor, two distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity, which is then removed to leave an air gap, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors shows a wide tuning range, and high percentage transmission is achieved with a tuning voltage of only 7.5 V. The full-width at half-maximum ranged from 95 to 105 nm over a tuning range of 2.2-1.85 /spl mu/m.     

InAlGaAs bulk micromachined tunable Fabry–Pérot filter for dense WDM systems

In this work we report on micromechanically tunable Fabry–Pérot filter concepts for wavelength division multiplexing (WDM) systems. The optical resonator is designed for a cavity length around 30 μm in order to increase the filter selectivity while relaxing the demands on the required mirror reflectance. The introduction of micromechanical actuators, utilizing electrothermal and electrostatic principles, allows wavelength tuning of the filter over a range of more than 40 nm in the 1.55 μm wavelength regime. The movable Bragg mirror, designed as suspended membrane and fabricated with an InP bulk-micromachining technology, consists of a molecular beam epitaxy-grown InAlGaAs quarter-wavelength multilayer stack. The influence of micromechanical actuation and the effect of intrinsic mechanical stress on the mirror deformation has been investigated systematically to optimize the optical filter performance. Filter losses induced by the light absorption within the epitaxial Bragg mirror have been minimized using a highly doped InGaAs/InAlAs composition. Furthermore, low-loss Fabry–Pérot filters have been fabricated using InAlGaAs/InAlAs Bragg mirrors. The measured full-width at half-maximum (FWHM) is 0.24 nm and a filter insertion loss of 2.8 dB has been observed. The FWHM is kept below 0.35 nm over an entire tuning range of 40 nm for an actuation power of 1.3 mW. The bulk-micromachining technology presented here is open for the future development of WDM components, e.g. tunable receivers or laser diodes.     

Thin stoichiometric silicon nitride prepared by r.f. reactive sputtering

Thin silicon nitride films were prepared on silicon wafers at deposition rates of 4 nm/min to 56 nm/min by r.f. reactive sputtering. Various mechanical, chemical and optical properties were investigated as a function of r.f. power, gas composition and temperature by means of AFM, RBS, XPS and an ellipsometer. Chemical stoichiometric films, with N-to-Si atomic ratio of 4:3 and refractive index of 2.0 were achieved even at room temperature. An interference filter for a UV detector with central wavelength of 254 nm was manufactured based on sputtered nitride, aluminum and silicon dioxide.     

Molecular beam epitaxy grown long wavelength infrared HgCdTe on Si detector performance

The use of silicon as a substrate alternative to bulk CdZnTe for epitaxial growth of HgCdTe for infrared (IR) detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low defect density HgCdTe on silicon where the lattice mismatch is ∼19%. This is especially true for LWIR HgCdTe detectors where the performance can be limited by the high (∼5×10⁶ cm⁻²) dislocation density typically found in HgCdTe grown on silicon. We have fabricated a series of long wavelength infrared (LWIR) HgCdTe diodes and several LWIR focal plane arrays (FPAs) with HgCdTe grown on silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific’s planar diode architecture. The diode and FPA and results at 78 K will be discussed in terms of the high dislocation density (∼5×10⁶ cm²) typically measured when HgCdTe is grown on silicon substrates.     

组合套镀法制备2.0～2.4 μm波段8通道微型集成滤光片

利用组合套镀法布里珀罗结构光学薄膜滤光片间隔层的方法,选取锗和一氧化硅分别作为高低折射率膜层材料,在短波红外区域2.0～2.4 μm光谱范围内,设计并制备了8通道集成窄带滤光片,单个光谱通道的有效通光区域的宽度为450 μm,其间有30 μm的挡光过渡带。各通道的峰值光谱透射率大于65%,滤光片的半峰全宽为8～13 nm,相对带宽在0.33%～0.65%之间。     

低电压驱动的MEMS F-P可调光学滤波器研究

基于微机电系统（MEMS）技术,研制了一种新颖的光学腔与静电驱动器分离的Fabry-Pérot（F-P）可调谐滤波器。从光学设计、MEMS结构设计、制造工艺与器件测试等开展了F-P可调谐滤波器的研究,成功制备了工作在以1550 nm波长为中心、调谐范围为40 nm和驱动电压低于30 V的MEMS F-P可调滤波器。测试...     

Vertical coupled-cavity microinterferometer on GaAs withdeformable-membrane top mirror

Fabry-Perot microinterferometer is demonstrated that combines a GaAs-AlAs vertical cavity with a suspended movable membrane. Electrostatic displacement of the gold/silicon nitride membrane allows for broad and continuous wavelength tuning of the cavity resonance formed by the combination of the GaAs cavity and the air gap below the membrane. The device exhibits a 32-nm tuning range around the 920-nm center wavelength for 0-14 V applied bias and FWHM linewidths near 3 nm; this corresponds to membrane deflections of up to 0.27 μm. Such structures provide the foundation for wavelength selective photodiodes, light emitters, and lasers in which the active wavelength is under voltage control     

基于MATLAB红外双波段成像探测器性能仿真

红外双波段成像探测器能接收目标和干扰源在两个波段上的辐射能量.从普朗克黑体辐射定律出发,根据MATLAB软件模拟出的目标和干扰源的辐射特性来选择SW/MW两个红外波段.首先利用仿真程序计算InSb面阵探测器对于点黑体和面黑体的响应结果,由计算结果和测试结果较好的一致性,说明设计的MATLAB仿真程序具有实用性.再从实际研制的HgCdTe 128×128叠层式双波段器件结构考虑,通过一定的变换,利用仿真程序对HgCdTe SW/MW双波段成像探测器进行参数性能仿真,达到利用成像及双色比来区分目标和干扰的目的.     

Monolithically integrated HgCdTe focal plane arrays

The cost and performance of hybrid HgCdTe infrared (IR) focal plane arrays are constrained by the necessity of fabricating the detector arrays on a CdZnTe substrate. These substrates are expensive, fragile, available only in small rectangular formats, and are not a good thermal expansion match to the silicon readout integrated circuit. We discuss in this paper an IR sensor technology based on monolithically integrated IR focal plane arrays that could replace the conventional hybrid focal plane array technology. We have investigated the critical issues related to the growth of HgCdTe on Si read-out integrated circuits and the fabrication of monolithic focal plane arrays: (1) the design of Si read-out integrated circuits and focal plane array layouts; (2) the low-temperature cleaning of Si(001) wafers; (3) the growth of CdTe and HgCdTe layers on read-out integrated circuits; (4) diode creation, delineation, electrical, and interconnection; and (4) demonstration of high yield photovoltaic operation without limitation from earlier preprocessing such as substrate cleaning, molecular beam epitaxy (MBE) growth, and device fabrication. Crystallographic, optical, and electrical properties of the grown layers will be presented. Electrical properties for diodes fabricated on misoriented Si and readout integrated circuit (ROIC) substrates will be discussed. The fabrication of arrays with demonstrated I–V properties show that monolithic integration of HgCdTe-based IR focal plane arrays on Si read-out integrated circuits is feasible and could be implemented in the third generation of IR systems.     

A silicon-based integrated NMOS-p-i-n photoreceiver

For large-volume optoelectronics applications, the low cost, manufacturability and reliability of silicon MOSFET technology are advantageous. In addition, silicon photodetectors operate quite efficiently at the 850 nm wavelength of economical AlGaAs light sources. In this paper, we report on a silicon-based monolithic optical receiver. The fabrication of the integrated lightwave receiver was carried out on a nominally undoped p-type Si substrate. The p-i-n photodetector was fabricated directly on the high-resistivity substrate so that the thickness of the detector depletion layer was approximately equal to the optical absorption length of 850 nm light in silicon. A more heavily-doped p-well was formed for the NMOSFET fabrication. The silicon photodiodes had a dark current of 20 nA at 5 V, a breakdown voltage greater than 60 V, and a zero-bias capacitance of 40 fF. The external quantum efficiency of the photodiode at 870 nm was approximately 67% at 5 V without an AR coating, and the bandwidth of the device was approximately 1.3 GHz. Frequency response evaluation of the receiver indicated a circuit-design-limited bandwidth of 30 MHz with open eye diagrams demonstrated at 40 MB/s     

Continuous wavelength tuning in micromachined Littrow external-cavity lasers

This work presents the theory and experiment of the wavelength continuously tunable lasers, whose external cavities are constructed by the microelectromechanical systems (MEMS) technology. The theoretical study reexamines the wavelength tuning theory and adapts it to the MEMS tunable lasers under special concerns of the system properties such as short cavity length and prealigned component position. It is shown that in the MEMS Littrow lasers a mode-hop-free wavelength tuning requires a moving pivot, or in other words, a fixed pivot has only limited tuning range. In addition, it is also found that the wavelength dependence of the gain medium refractive index significantly affects the wavelength tuning range. Based on the theoretical study, a tuning structure is fabricated by the deep reactive ion etching (DRIE) on a silicon-on-insulator (SOI) wafer, and hybridly integrated with a gain chip and an optical fiber. The laser has dimensions as small as 2.0 mm/spl times/1.5 mm/spl times/0.6 mm, and can be tuned continuously over 30.3 nm at a resolution of 0.03 nm/V/sup 2/. As a comparison, another MEMS tunable laser designed according to the conventional theory has only a tuning range of 5.9 nm.     

Room-temperature optically pumped InAs/GaAs quantum dots microdisk lasers on SiO2/Si chip

We report on room temperature continuous-wave optically pumped InAs/GaAs quantum dot whispering gallery mode microdisk lasers,heterogeneously integrated on silica/silicon chips.The microdisks are fabricated by photolithography and inductively coupled plasma etching.The lasing wavelength is approximately 1200 nm and the obtained lowest laser threshold is approximately 28μW.The experimental results show an approach of possible integrated Ⅲ-Ⅴ optical active materials on silica/silicon chip for low threshold WGM microdisk lasers.     

Elastooptical properties of SiON layers in an integrated opticalinterferometer used as a pressure sensor

This work presents the design and realization of an integrated optical pressure sensor, which is based on the photoelastic birefringence of thin SiO₂ and SiON layers. The advantage of this well known and controlled silicon technology is that optical and electronic circuits as well as micromechanics can be integrated on the same substrate. The sensor is made of a monomode striploaded Mach-Zehnder interferometer, which is placed on a silicon membrane as the pressure sensitive region. The detector is integrated into the silicon substrate, because a wavelength below 1 μm(He-Ne laser source: 632.8 nm) is used. Experimental and theoretical results of the sensor response are presented that demonstrate that efficient sensors can be designed and fabricated and that the TM-polarization gives the higher sensitivity     

1.55μm非晶硅热光F-P腔可调谐滤波器

介绍了一种Si基热光Fabry-Perot (F-P)腔可调谐滤波器.F-P腔由电子束蒸发的非晶硅构成.利用非晶硅的热光效应,通过对Si腔加热,改变F-P腔的折射率,从而引起透射峰位的红移.该原型器件调谐范围为12nm,透射峰的FWHM(峰值半高宽)为9nm,加热效率约为0.1K/mW.精确控制DBR(分布式Bragg反射镜)生长获得高反射率镜面是减小带宽的有效途径;通过改进加热器所处位置及增强散热能力,有望进一步提高加热效率.     

碲镉汞红外双色探测器响应光谱研究

报道了集成碲镉汞红外双色焦平面探测芯片光谱特性研究的初步结果.针对HgCdTe红外双色探测原型芯片短波响应光谱偏窄的现象,展开了双色探测芯片光谱特性与结构特性内在关系的理论分析和实验研究,发现了SW响应光谱窄的起因和解决思路,并获得了优化结构的双色探测芯片正常的光谱响应曲线     

Independently accessed back-to-back HgCdTe photodiodes: A new dual-band infrared detector

We report the first data for a new two-color HgCdTe infrared detector for use in large dual-band infrared focal plane arrays (IRFPAs). Referred to as the independently accessed back-to-back photodiode structure, this novel dual-band HgCdTe detector provides independent electrical access to each of two spatially collocated back-to-back HgCdTe photodiodes so that true simultaneous and independent detection of medium wavelength (MW, 3–5 μm) and long wavelength (LW, 8–12 μm) infrared radiation can be accomplished. This new dual-band detector is directly compatible with standard backside-illuminated bump-interconnected hybrid HgCdTe IRFPA technology. It is capable of high fill factor, and allows high quantum efficiency and BLIP sensitivity to be realized in both the MW and LW photodiodes. We report data that demonstrate experimentally the key features of this new dual-band detector. These arrays have a unit cell size of 100 x 100 μm², and were fabricated from a four-layer p-n-N-P HgCdTe film grown in situ by metalorganic chemical vapor deposition on a CdZnTe substrate. At 80K, the MW detector cutoff wavelength is 4.5 μm and the LW detector cutoff wavelength is 8.0 μm. Spectral crosstalk is less than 3%. Data confirm that the MW and LW photodiodes are electrically and radiometrically independent.     

A novel high-speed silicon MSM photodetector operating at 830 nmwavelength

A novel high-speed silicon photodetector that operates at a wavelength of 830 nm is reported. It consists of a Metal-Semiconductor-Metal (MSM) detector that is fabricated on a 5-μm thick silicon membrane. The detector has a measured -3 dB bandwidth of 3 GHz at 10 V, which is almost one order of magnitude larger than the reported bandwidth of conventional silicon MSM detectors as measured at 830 nm. The DC responsivity is 0.17 A/W, corresponding to an internal quantum efficiency of 60.5% and an external quantum efficiency of 25.4%. The large bandwidth and good responsivity at the wavelength of interest, combined with its low operating voltage and compatibility with most silicon integrated circuit technologies, make this detector a promising candidate for monolithic optoelectronic receiver circuits for use in short distance optical communication systems and computer interconnects     

A high-speed, high-sensitivity silicon lateral trench photodetector

We report a novel silicon lateral trench photodetector that decouples the carrier transit distance from the light absorption depth, enabling both high speed and high responsivity. The photodetector, fabricated with fully VLSI compatible processes, exhibits a 6-dB bandwidth of 1.5 GHz at 3.0 V and an external quantum efficiency of 68% at 845 nm wavelength. A photoreceiver with a wire-bonded lateral trench detector and a BiCMOS transimpedance amplifier demonstrates excellent operation at 2.5 Gb/s data rate and 845 nm wavelength with only a 3.3 V bias     

基于谐振原理的RF MEMS滤波器的研制

采用与IC工艺兼容的硅表面MEMS加工技术,以碳化硅材料作为结构材料,研制出一种新型的基于谐振原理工作的RF MEMS滤波器。详细介绍了器件的工作原理、制备方法、测试技术和结果,并对测试结果做出分析。该RF MEMS滤波器由弹性耦合梁连接两个结构尺寸和谐振频率完全相同的MEMS双端固支梁谐振器构成,MEMS谐振器的结构决定了滤波器的中心频率,弹性耦合梁的刚度决定了滤波器的带宽。在大气环境下测试器件的频响特性,得到中心工作频率为41.5MHz,带宽为3.5MHz,品质因数Q为11.8。     

High performance SWIR HgCdTe detector arrays

Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ∼3.5 μm and cap layer thickness was ∼0.4 μm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (∼3-5X below theory). Band 5 detector performance was ∼4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 μm detector on 45 μm × 60 μm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5−1.75 μm) and Landsat Band 7 (2.08−2.35 μm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ∼99% at 10¹² cm Hz^1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz ^1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally <20 μm μm) planar-mesa diodes to the microlens size of 48 urn. Using microlenses allows array performance to exceed 1-D theory up to a factor of 5.