Scaled CMOS technologies with low sheet resistance at 0.06-μmgate lengths

A novel Ti self-aligned silicide (salicide) process using a combination of low dose molybdenum and preamorphization (PAI) implants and a single rapid-thermal-processing (RTP) step is presented, and shown to be the first Ti salicide process to achieve low sheet resistance at ultrashort 0.06-μm gate lengths (mean=5.2 Ω/sq, max=5.7 Ω/sq at 0.07 μm; mean=6.7 Ω/sq, max=8.1 Ω/sq at 0.06 μm, TiSi₂ thickness on S/D=38 nm), in contrast with previous Ti salicide processes which failed below 0.10 μm. The process was successfully implemented into a 1.5 V, 0.12-μm CMOS technology achieving excellent drive currents (723 and 312 μA/μm at I_OFF=1 nA/μm for nMOS and pMOS, respectively)     

Crown-shaped stacked-capacitor cell for 1.5-V operation 64-Mb DRAMs

A self-aligned stacked-capacitor cell called the CROWN cell (a crown-shaped stacked-capacitor cell), used for experimental 64-Mb-DRAMs operated at 1.5 V, has been developed using 0.3-μm electron-beam lithography. This memory cell has an area of 1.28 μm². The word-line pitch and sense-amplifier pitch of this cell are 0.8 and 1.6 μm, respectively. In spite of this small cell area, the CROWN cell has a large capacitor surface area of 3.7 μm² because (1) it has a crown-shaped capacitor electrode, (2) its capacitor is on the data line, and (3) it has a self-aligned memory cell fabrication process and structure. The large capacitor area and a Ta₂O₅ film equivalent to a 2.8-nm SiO₂ film ensure a large storage charge of 33 fC (storage capacitance equals 44 fF) for 1.5-V operation. A small CROWN cell array and a memory test circuit were successfully used to achieve a basic DRAM cell operation     

High-frequency performance of diamond field-effect transistor

The microwave performance of a diamond metal-semiconductor field-effect transistor (MESFET) is reported for the first time. MESFETs with a gate length of 2-3 μm and a source-gate spacing of 0.1 μm were fabricated on the hydrogen-terminated surface of an undoped diamond film grown by microwave plasma chemical vapor deposition (CVD) utilizing a self-aligned gate fabrication process. A maximum transconductance of 70 mS/mm was obtained on a 2 μm gate MESFET at V_GS=-1.5 V and V_DS=-5 V,for which a cutoff frequency f_T and a maximum oscillating frequency f_max of 2.2 GHz and 7 GHz were obtained, respectively     

Photonic crystal line defect waveguide directional coupler

A three-port directional coupler based on photonic crystal line defect waveguides is demonstrated. The directional coupler has only a 21 μm long coupling region. Wavelength-selecting operation around 1.5 μm wavelength was confirmed     

Single mode multiple-element laser array with grating filter

A 1.5-μm wavelength grating filter laser array (GFA) structure which consists of a positive-index-guided multiple-element array region and a laterally unguided grating filter region is proposed and theoretically analyzed for realizing in-phase supermode and simultaneous single-longitudinal-mode operation. A five-element GaInAsP/InP GFA with a lasing wavelength of ~1.5 μm was fabricated and its single-longitudinal-mode/in-phase supermode operation was demonstrated up to four times the threshold current     

Self-aligned AlGaAs/GaAs HBT with low emitter resistance utilizingInGaAs cap layer

A self-aligned AlGaAs/GaAs heterojunction bipolar transistor (HBT) with an InGaAs emitter cap layer that has very low emitter resistance is described. In this structure, a nonalloyed emitter contact allows the emitter and base electrodes to be formed simultaneously and in a self-aligned manner. The reduction of emitter resistance greatly improves the HBT's transconductance and cutoff frequency. In fabricated devices with emitter dimensions of 2 μm×5 μm, a transconductance-per-unit-area of 16 mS/μm² and a cutoff frequency of 80 GHz were achieved. To investigate high-speed performance, a 21-stage ECL ring oscillator was fabricated using these devices. Propagation delay times as low as 5.5 ps/gate were obtained, demonstrating the effectiveness of this structure     

A high-speed bipolar technology featuring self-aligned single-polybase and submicrometer emitter contacts

An experimental bipolar transistor structure with self-aligned base-emitter contacts formed using one polysilicon layer is presented with geometries and frequency performance comparable to those of double-polysilicon structures. This structure, called STRIPE (self-aligned trench-isolated polysilicon electrodes), provides a 0.2-μm emitter-base polysilicon contact separation. A 0.4-μm emitter width is achieved with conventional 0.8-μm optical lithography. Scaling of the emitter width of 0.3 μm has been performed with minimal degradation of device performance, and scaling of the emitter width pattern to 0.2 μm has been demonstrated. These dimensions are the smallest achieved in single-polysilicon structures with polysilicon base contacts and are comparable to those achieved in double-polysilicon structures. The STRIPE structure has been used to fabricate transistors with f_t as high as 33.8 GHz     

High transconductance and velocity overshoot in NMOS devices at the0.1-μm gate-length level

Transport properties are investigated in self-aligned NMOS devices with gate lengths down to 0.07 μm. Velocity overshoot was observed in the form of the highest transconductances measured to date in Si FETs, as well as in the trend of the transconductance with gate length. The measured transconductance reached 910 μS/μm at liquid-nitrogen temperature and 590 μS/μm at room temperature. Velocity overshoot, by making such transconductances possible, should extend the value of miniaturization to dimensions that are smaller than what was commonly assumed to be worthwhile to pursue     

Fused taper/filter hybrid single-mode wavelength divisionmulti/demultiplexer

A low loss and low crosstalk single-mode wavelength division multi/demultiplexer was successfully fabricated by embedding an interference filter in each output arm of a fused taper coupler. The insertion loss was around 1.5 dB at the wavelengths of 1.3 μm and 1.55 μm, and both near-end and far-end crosstalks were less than -50 dB     

1.5 μm wavelength distributed reflector lasers with verticalgrating

A 1.5 μm wavelength distributed reflector laser, consisting of a distributed Bragg reflector rear facet and a distributed feedback region, was realised using deep-etching technology. A low threshold current of I_th=12.4 mA and a high differential quantum efficiency of η_d=42% from the front facet was achieved with a submode suppression ratio of 33 dB (I=2.4 I_th) for a fifth-order grating, 220 μm long and 6 μm wide device at room temperature     

High-speed operation of 1.5 μm GaInAsP/InP optoelectronicintegrated laser drivers

A 1.5 μm-wavelength high-speed self-aligned constricted-mesa laser diode and an InP MESFET have been integrated monolithically without deterioration in the performance of either device, by using a gate projection process. A broad 3 dB bandwidth of 6.6 GHz was demonstrated for the first time     

An ultra-high-speed ECL-BiCMOS technology with silicon filletself-aligned contacts

We have developed a half-micron super self-aligned BiCMOS technology for high speed application. A new SIlicon Fillet self-aligned conTact (SIFT) process is integrated in this BiCMOS technology enabling high speed performances for both CMOS and ECL bipolar circuits. In this paper, we describe the process design, device characteristics and circuit performance of this BiCMOS technology. The minimum CMOS gate delay is 38 ps on 0.5 μm gate and 50 ps on 0.6 μm gate ring oscillators at 5 V. Bipolar ECL gate delay is 24 ps on 0.6 μm emitter ring oscillators with collector current density of 40 kA/cm². A single phase decision circuit operating error free over 8 Gb/s and a static frequency divider operating at 13.5 GHz is demonstrated in our BiCMOS technology     

Design of double and triple quantum wells for InGaAs-AlAsSbintersubband unipolar semiconductor lasers

InGaAs-AlAsSb double and triple quantum well (QW) structures were designed in an effort to shorten the wavelength to less than 2 μm for possible application to intersubband unipolar lasers. Wavelengths corresponding to the intersubband separation, the minimum and maximum operating electric field, optical-phonon-limited nonradiative scattering time, and escape time from the QW were simulated. It was found that suitable nonradiative transition times can be obtained by properly designing the coupling layer thickness for both kinds of QW's. The minimum wavelength is 1.5 μm and an operating electric field is above 130 kV/cm for wavelengths <2 μm in the double QW. On the other hand, the minimum operating electric field is less than 10 kV/cm and the minimum wavelength is about 1.7 μm for the triple QW. The triple QW is suitable for an electric-field induced wavelength tunable laser     

Partially depleted SOI NMOSFET's with self-aligned polysilicon gateformed on the recessed channel region

A new SOI NMOSFET with a “LOCOS-like” shape self-aligned polysilicon gate formed on the recessed channel region has been fabricated by a mix-and-match technology. For the first time, we developed a new scheme for implementing self-alignment in both source/drain and gate structure in recessed channel device fabrication. Symmetric source/drain doping profile was obtained and highly symmetric electrical characteristics were observed. Drain current measured from 0.3 μm SOI devices with V_z of 0.773 V and T_ox=7.6 nm is 360 μA/μm at V_GS=3.5 V and V _DS=2.5 V. Improved breakdown characteristics were obtained and the BV_DSS (the drain voltage for 1 nA/μm of I_D at T_GS=0 V) of the device with L_eff=0.3 μm under the floating body condition was as high as 3.7 V     

Singlemode output power enhancement of InGaAs VCSELs by reducedspatial hole burning via surface etching

Completely singlemode MBE-grown selectively oxidised InGaAs-VCSELs with aperture diameters of up to 14 μm have been fabricated using a self-aligned shallow surface etch. By choosing the growth position accordingly, a continuous variation of the aperture diameter across the wafer is achieved to optimise the surface etch to aperture diameter ratio. A record singlemode output power of 5.7 mW (30 dB SMSR) is obtained for a 5.8 μm-aperture diameter, 2.8 μm etch spot diameter device     

Integration of GalnP/GaAs heterojunction bipolar transistors andhigh electron mobility transistors

Integration of carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs) is demonstrated by growing an HBT on the top of a HEMT. A current gain of 60, a cutoff frequency of 59 GHz and a maximum oscillation frequency of 68 GHz were obtained for a 5×15 μm² self-aligned HBT. The HEMT, with a gate length of 1.5 μm has a transconductance of 210 mS/mm, a cutoff frequency of 9 GHz and a maximum oscillation frequency of 22 GHz. It is shown that the GaInP/GaAs HBT on the HEMT is a simple Bi-FET technology suitable for microwave and mixed signal applications     

High contrast GaInAs:Fe photoconductive optical AND gate fortime-division demultiplexing

A high-contrast, three port optical AND gate based on the photoconductive effect in Ga_0.47In_0.53As:Fe and operating in the λ=1.3-5 μm wavelength range is demonstrated. A 250:1 optical power contrast ratio (or 48 dB in electrical power after detection) is obtained in an optical-to-optical time division demultiplexing of a 100 MHz pulse train by a 6.25 MHz clock, both at λ=1.3 μm, with the demultiplexed output pulses at λ=1.5 μm     

A new lensed-fiber configuration employing cascaded GI-fiber chips

A new scheme is proposed for lensed fibers having high coupling efficiency between laser diodes and single-mode fibers with a long working distance. The new lensed fiber consists of a pair of GI-fiber tips having different focusing parameters. The measured net coupling loss between a laser diode operating at a wavelength of 1.3 μm and a single-mode fiber is as low as 1.5 dB. The working distances are around 50 μm, much longer than those of conventional lensed fibers     

A novel self-aligned fabrication process for nickel-indiffusedlithium niobate ridge optical waveguides

A novel self-aligned fabrication process for LiNbO₃:Ni ridge waveguides has been proposed. By using the self-aligned trilayered structure composed of Ni-Ti-Si, the fabrication process is significantly simplified, and takes advantage of suppression of the unwanted planar waveguides and high-coupling efficiency to a single-mode fiber as compared to the conventional processes. Detailed investigations into the characteristics of the ridge waveguides have also proved to be informative under different fabrication parameters. Moreover, the novel self-aligned fabrication process was applied to fabricate a ridge waveguide Mach-Zehnder modulator. The measured half-wave voltage and extinction ratio mere 20.5 V and 12 dB (@1.3 μm), and were 4.2 V and 8 dB (@0.6328 £gm)     

1.5-μm wavelength tunable phase-shift-controlled distributedfeedback laser

A 1.5 μm wavelength tunable phase-shift-controlled distributed feedback laser diode is studied. This wavelength tunable laser controls the light output power and the oscillation wavelength independently by current injection. During wavelength tuning, the submode suppression ratio is large and an almost constant spectral linewidth from 24 to 29 MHz is achieved over a wavelength tuning range as wide as 113 GHz (9.0 Å). The threshold gain change and the loss change are small during wavelength tuning and as a result an almost constant light output power is achieved