A method to tune the cavity-mode wavelength of resonant cavity-enhanced photodetectors for bidirectional optical interconnects

A method to tune the cavity-mode wavelength of resonant cavity-enhanced photodetectors (RCE-PDs) is proposed. The proposed method can enable monolithic integration of vertical-cavity surface-emitting lasers and RCE-PDs to be a cost-competitive choice for bidirectional optical interconnection by reducing the amount of component and packaging costs presently involved. The properly tuned cavity-mode wavelengths remain effectively aligned within a temperature range of -10/spl deg/C/spl sim/50/spl deg/C.     

Fabrication of Germanosilicate glass optical fibers containing Tm/sup 2+/ ions and their nonlinear optical properties

Germanosilicate glass optical fibers incorporated with the Tm/sup 2+/ ions were fabricated to enhance optical nonlinearity by providing a strong reduction environment based on the solution doping technique in the modified chemical vapor deposition (MCVD) process. The incorporation of the Tm/sup 2+/ ions into the fiber core was identified by the electron paramagnetic resonance (EPR) spectrum in the fiber preform, and the absorption and emission properties between 350 and 1600 nm of the Tm/sup 2+/ ions in optical fibers and the fiber preform. A strong broad absorption band due to the Tm/sup 2+/ ions appeared from 350 to /spl sim/900 nm, and a broad emission from /spl sim/600 to /spl sim/1050 nm and the other emission from /spl sim/1050 to /spl sim/1300 nm, which were not shown in the Tm/sup 3+/ ions, were found upon Ar-ion laser pumping at 515 nm. Both absorption and emission results confirm that the Tm/sup 2+/ ions in the germanosilicate glass have the 4f-5d energy band from 350 to /spl sim/900 nm and the 4f-4f energy level at /spl sim/1115 nm. Also, the resonant nonlinearity at /spl sim/1310 and /spl sim/1530 nm due to the Tm/sup 2+/ ions in the fiber was measured upon the 515 nm optical pumping by using a long-period fiber grating (LPG) pair method. The nonlinear refractive index n/sub 2/ at /spl sim/1310 and /spl sim/1530 nm was found to be /spl sim/4/spl times/10/sup -15/ m/sup 2//W, where 70% and 30% of the n/sub 2/ are attributed to the nonradiative transitions and the radiative transitions, respectively.     

Low-voltage high performance compact all cascode CMOS current mirror

A high performance and compact current mirror with extremely low input and high output resistances (R/sub in//spl sim/0.01/spl Omega/, R/sub out//spl sim/10 G/spl Omega/), high copying accuracy, very low input and output voltage requirements (V/sub in/, V/sub out//spl ges/V/sub DSsat/), high bandwidth (200 MHz using a 0.5 /spl mu/m CMOS technology) and low settling time (25 ns) is proposed. Simulations and experimental results are shown that validate the circuit.     

Light-output enhancement in a nitride-based light-emitting diode with 22/spl deg/ undercut sidewalls

We successfully fabricated nitride-based light-emitting diodes (LEDs) with /spl sim/22/spl deg/ undercut sidewalls. The /spl sim/22/spl deg/ etching undercut sidewalls were achieved by controllable inductively coupled plasma reactive ion etching. With a 20-mA current injection, the output powers of the LED with /spl sim/22/spl deg/ undercut sidewalls and standard LED were 5.1 and 3 mW, respectively-a factor of 1.7 times enhancement. It was found that such undercut sidewalls could enhance the probability of escaping the photons outside from the LED in the near horizontal and in-plane directions. This simple and controllable method is beneficial to fabricate brighter LEDs.     

5/spl times/9 integrated optical star coupler in silicon-on-insulator technology

We describe fabrication of the first optical star coupler in silicon-on-insulator (SOI) technology. The 5/spl times/9 coupler consists of two silicon rib waveguide arrays with a radiative slab waveguide region. The star geometry was analyzed and designed using the beam propagation method. The coupler exhibits low loss (average excess insertion loss /spl alpha//spl sim/1.3 dB) and good coupling uniformity (standard deviation /spl sigma//spl sim/1.4 dB) at /spl lambda/=1.55 /spl mu/m. It represents a key component for realization of photonic circuits in a silicon integrated circuit technology.     

Corner-fed microstrip antenna element and arrays for dual-polarization operation

A systematic study on the dual-polarized corner-fed microstrip antenna element and arrays with thin single-layer structure is presented. The impedance matrices and S-parameters of the element and arrays are investigated by the proposed extended multiport network method (EMNM). The co- and cross-polarization patterns are also analyzed. It is shown that this kind of antenna element has an isolation about 10 dB higher than that of a conventional edge-fed square patch. A series of new dual-polarized arrays of corner-fed patches have been designed and analyzed based on the EMNM. The experimental results of five arrays indicate that these arrays achieve an isolation of 27/spl sim/38 dB with a maximum of higher than 28/spl sim/58 dB and cross-polarization level of lower than -23/spl sim/ -30 at boresight, which are substantially better than those of similar dual-polarized arrays of edge-fed patches. All theoretical results are in good agreement with experimental ones.     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

Integrated high-/spl kappa/ (/spl kappa/ /spl sim/19) MIM capacitor with Cu/low-/spl kappa/ interconnects for RF application

We demonstrate a high-performance metal-high /spl kappa/ insulator-metal (MIM) capacitor integrated with a Cu/low-/spl kappa/ backend interconnection. The high-/spl kappa/ used was laminated HfO/sub 2/-Al/sub 2/O/sub 3/ with effective /spl kappa/ /spl sim/19 and the low-/spl kappa/ dielectric used was Black Diamond with /spl kappa/ /spl sim/2.9. The MIM capacitor (/spl sim/13.4 fF//spl mu/m/sup 2/) achieved a Q-factor /spl sim/53 at 2.5 GHz and 11.7 pF. The resonant frequency f/sub r/ was 21% higher in comparison to an equivalently integrated Si/sub 3/N/sub 4/-MIM capacitor (/spl sim/0.93 fF//spl mu/m/sup 2/) having similar capacitance 11.2 pF. The impacts of high-/spl kappa/ insulator and low-/spl kappa/ interconnect dielectric on the mechanism for resonant frequency improvement are distinguished using equivalent circuit analysis. This letter suggests that integrated high-/spl kappa/ MIM could be a promising alternative capacitor structure for future high-performance RF applications.     

New addressing method using overlapping scan time of AC-PDP

A new plasma display panel driving method was proposed to reduce the address period. The scan time of the address method using overlapping scan time overlaps with the next scan time during the formative lag time of the discharge. Thus, without reducing the address pulsewidth and the scan pulsewidth, the driving method can reduce the address period. We could overlap the scan time of about 100 /spl sim/300 ns. However, the driving method has a narrow address voltage margin compared with a conventional method. In order to improve the address voltage margin of the driving method, the scan direction is set to the opposite direction compared with the conventional direction. As shown in experimental results, the address voltage margin of the new driving method is increased by 7/spl sim/10 V when the opposite scan direction is used.     

Compact wideband antenna for 2.4 GHz WLAN applications

A novel compact wideband antenna for wireless local area network (WLAN) applications in the 2.4 GHz band is presented. The proposed low profile antenna of dimensions 15/spl times/14.5/spl times/1.6 mm offers 18.6% bandwidth and an average gain of /spl sim/5 dBi. The antenna can be excited directly using a 50 /spl Omega/ coaxial probe.     

Fiber design for broad-band gain-flattened Raman fiber amplifier

We report here a novel fiber design which has inherently flattened effective Raman gain spectrum, with a relative 3-dB bandwidth of /spl sim/90 nm. Gain-flattened broad-band amplification can be achieved in any wavelength band by suitably choosing the fiber parameters and the pump wavelength. Simulations show that the proposed fiber also has high negative dispersion coefficient /spl sim/(-300 to -600) ps/km /spl middot/ nm in the operating range of wavelength. Hence, the designed fiber serves the purpose of a gain-flattened broad-band amplifier and dispersion compensator.     

Optical and electrical properties of nanostructured metal-silicon-metal photodetectors

We report an experimental evaluation of the performance of silicon (Si) photodetectors incorporating one-dimensional (1-D) arrays of rectangular and triangular-shaped nanoscale structures within their active regions. A significant (/spl sim/2/spl times/) enhancement in photoresponse is achieved in these devices across the 400- to 900-nm spectral region due to the modification of optical absorption properties that results from structuring the Si surface on physical optics scales smaller than the wavelength, which both reduces the reflectivity and concentrates the optical field closer to the surface. Both patterned (triangular and rectangular lineshape) and planar Ni-Si back-to-back Schottky barrier metal-semiconductor-metal photodetectors on n-type (/spl sim/5/spl times/10/sup 14/ cm/sup -3/) bulk Si were studied. 1-D /spl sim/50-250-nm linewidth, /spl sim/1000-nm depth, grating structures were fabricated by a combination of interferometric lithography and dry etching. The nanoscale grating structures significantly modify the absorption, reflectance, and transmission characteristics of the semiconductor: air interface. These changes result in improved electrical response leading to increased external quantum efficiency (from /spl sim/44% for planar to /spl sim/81% for structured devices at /spl lambda/=700 nm). In addition, a faster time constant (/spl sim/1700 ps for planar to /spl sim/600 ps for structured at /spl lambda/=900 nm) is achieved by increasing the absorption near the surface where the carriers can be rapidly collected. Experimental quantum efficiency and photocurrents results are compared with a theoretical photocurrent model based on rigorous coupled-wave analysis of nanostructured gratings.     

Long-wavelength In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As large-area avalanche photodiodes and arrays

Large-area (500-/spl mu/m diameter) mesa-structure In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiodes (APDs) are reported. The dark current density was /spl sim/2.5/spl times/10/sup -2/ nA//spl mu/m/sup 2/ at 90% of breakdown; low surface leakage current density (/spl sim/4.2 pA//spl mu/m) was achieved with wet chemical etching and SiO/sub 2/ passivation. An 18 /spl times/ 18 APD array with uniform distributions of breakdown voltage, dark current, and multiplication gain has also been demonstrated. The APDs in the array achieved 3-dB bandwidth of /spl sim/8 GHz at low gain and a gain-bandwidth product of /spl sim/120 GHz.     

A fiber Bragg grating sensor system for simultaneously static and dynamic measurements with a wavelength-swept fiber laser

A novel fiber Bragg grating (FBG) sensor system for static and dynamic measurements with a wavelength-swept fiber laser is proposed and demonstrated. In this system, both static and dynamic perturbation of each FBG in the sensor arrays can be interrogated simultaneously. The experiments demonstrated the strain resolutions of /spl sim/1 /spl mu//spl epsiv/ and 3.4 n/spl epsiv///spl radic/Hz at 500 Hz for static and dynamic measurements, respectively.     

High-density MIM capacitors (/spl sim/85 nF/cm/sup 2/) on organic substrates

For the first time, transferring the prefabricated capacitors on a silicon wafer onto FR-4 has been used to realize high-density metal-insulator-metal (MIM) capacitors on an organic substrate. A high capacitance density /spl sim/85 nF/cm/sup 2/ was achieved on FR-4 substrate with PECVD silicon nitride as the dielectric layer. Excellent voltage coefficient (/spl sim/2.2 ppm/V/sup 2/) and temperature coefficient (/spl sim/38 ppm//spl deg/C) were obtained for capacitors on FR-4. Dielectric leakage and breakdown characteristics have been assessed, and the results demonstrated acceptable performance. Thus, this technology provides a new method to embed/integrate high-density capacitors on organic substrates for the system-in-package applications.     

The impact of uniform strain applied via bonding onto plastic substrate on MOSFET performance

For the first time, this letter presents a novel post-backend strain applying technique and the study of its impact on MOSFET device performance. By bonding the Si wafer after transistor fabrication onto a plastic substrate (a conventional packaging material FR-4), a biaxial-tensile strain (/spl sim/0.026%) was achieved globally and uniformly across the wafer due to the shrinkage of the bonded adhesive. A drain-current improvement (average /spl Delta/I/sub d//I/sub d//spl sim/10%) for n-MOSFETs uniformly across the 8-in wafer is observed, independent of the gate dimensions (L/sub g//spl sim/55 nm -0.530 /spl mu/m/W /spl sim/2-20 /spl mu/m). The p-MOSFETs also exhibited I/sub d/-improvement by /spl sim/7% under the same biaxial-tensile strain. The strain impact on overall device characteristics was also studied, including increased gate-induced drain leakage and short-channel effects.     

SOI technology for radio-frequency integrated-circuit applications

This paper presents a silicon-on-insulator (SOI) integration technology, including structures and processes of OFF-gate power nMOSFETs, conventional lightly doped drain (LDD) nMOSFETs, and spiral inductors for radio frequency integrated circuit (RFIC) applications. In order to improve the performance of these integrated devices, body contact under the source (to suppress floating-body effects) and salicide (to reduce series resistance) techniques were developed for transistors; additionally, locally thickened oxide (to suppress substrate coupling) and ultra-thick aluminum up to 6 /spl mu/m (to reduce spiral resistance) were also implemented for spiral inductors on high-resistivity SOI substrate. All these approaches are fully compatible with the conventional CMOS processes, demonstrating devices with excellent performance in this paper: 0.25-/spl mu/m gate-length offset-gate power nMOSFET with breakdown voltage (BV/sub DS/) /spl sim/ 22.0 V, cutoff frequency (f/sub T/)/spl sim/15.2 GHz, and maximal oscillation frequency (f/sub max/)/spl sim/8.7 GHz; 0.25-/spl mu/m gate-length LDD nMOSFET with saturation current (I/sub DS/)/spl sim/390 /spl mu/A//spl mu/m, saturation transconductance (g/sub m/)/spl sim/197 /spl mu/S//spl mu/m, cutoff frequency /spl sim/ 25.6 GHz, and maximal oscillation frequency /spl sim/ 31.4 GHz; 2/5/9/10-nH inductors with maximal quality factors (Q/sub max/) 16.3/13.1/8.95/8.59 and self-resonance frequencies (f/sub sr/) 17.2/17.7/6.5/5.8 GHz, respectively. These devices are potentially feasible for RFIC applications.     

640 /spl times/ 512 pixel long-wavelength infrared narrowband, multiband, and broadband QWIP focal plane arrays

A 640 /spl times/ 512 pixel, long-wavelength cutoff, narrowband (/spl Delta//spl lambda///spl lambda//spl sim/10%) quantum-well infrared photodetector (QWIP) focal plane array (FPA), a four-band QWIP FPA in the 4-15 /spl mu/m spectral region, and a broadband (/spl Delta//spl lambda///spl lambda/ /spl sim/ 42%) QWIP FPA having a 15.4 /spl mu/m cutoff have been demonstrated. In this paper, we discuss the electrical and optical characterization of these FPAs, and their performance. In addition, we discuss the development of a very sensitive (NEDT /spl sim/ 10.6 mK) 640 /spl times/ 512 pixel thermal imaging camera having a 9 /spl mu/m cutoff.     

Design and fabrication of zinc oxide thin-film ridge waveguides on silicon substrate with ultraviolet amplified spontaneous emission

Zinc oxide (ZnO) thin-film ridge waveguides have been designed and fabricated on n-type (100) silicon substrate. A filtered cathodic vacuum arc technique is used to deposit high-crystal-quality ZnO thin films on lattice-mismatched silicon substrates at 230/spl deg/C. A ridge waveguide of width /spl sim/2 /spl mu/m and height /spl sim/0.1 /spl mu/m is defined on the ZnO thin film by plasma etching. Room-temperature amplified spontaneous emission is observed with peak wavelength at /spl sim/385 nm under 355-nm optical excitation. It is found that the net optical gain of the ZnO thin-film ridge waveguides can be as large as 120 cm/sup -1/ at a pump intensity of /spl sim/1.9 MW/cm/sup 2/.     

High-performance fully depleted silicon nanowire (diameter /spl les/ 5 nm) gate-all-around CMOS devices

This paper demonstrates gate-all-around (GAA) n- and p-FETs on a silicon-on-insulator with /spl les/ 5-nm-diameter laterally formed Si nanowire channel. Alternating phase shift mask lithography and self-limiting oxidation techniques were utilized to form 140- to 1000-nm-long nanowires, followed by FET fabrication. The devices exhibit excellent electrostatic control, e.g., near ideal subthreshold slope (/spl sim/ 63 mV/dec), low drain-induced barrier lowering (/spl sim/ 10 mV/V), and with I/sub ON//I/sub OFF/ ratio of /spl sim/10/sup 6/. High drive currents of /spl sim/ 1.5 and /spl sim/1.0 mA//spl mu/m were achieved for 180-nm-long nand p-FETs, respectively. It is verified that the threshold voltage of GAA FETs is independent of substrate bias due to the complete electrostatic shielding of the channel body.