Ultra-thin Ta2O5dielectric film for high-speed bipolar memories

A new capacitor technology, with extremely thin (5.3-20 nm) Ta2O5film deposition and weak-spot oxidation, is developed to realize high capacitance and high reliability. The Ta2O5film was reactively sputtered, followed by weak-spot oxidation. The weak-spot oxidation is achieved by placing the Ta2O5film on Si in a high-temperature dry O2ambient. The oxidation significantly improves the time-dependent-dielectric-breakdown (TDDB) characteristics and reduces the defect density of Ta2O5capacitors without reducing the capacitance by selectively oxidizing the Si surface at weak spots where the Ta2O5is locally thin or missing. The technology is based on the new discovery that Ta2O5film less than 20 nm thick shows no reduction in dielectric breakdown strength after dry O2high-temperature annealing up to 1000° C. The Ta2O5(7.5-nm) capacitor with a capacitance of 8.5 fF/µm²is applied to a high-speed bipolar memory. This makes it possible to reduce the memory cell area to one-third that of a conventional bipolar memory. The memory provides high-speed operation; access time is less than 5 ns, and sufficient soft error immunity is provided.     

p-Channel TFT's using magnetron-sputtered Ta2O5films as gate insulators

Metal-gate thin-film transistors (TFT's) have been fabricated in layers of laser-recrystallized polycrystalline silicon on fused quartz substrates at processing temperatures below 625°C. Tantalum pentoxide (Ta2O5) was used as a gate insulator instead of a conventional thermally grown silicon dioxide (SiO2). Ta2O5gate insulator was deposited onto the recrystallized silicon layer at room temperature, using an RF-magnetron sputtering system. The reactive ion etching method, using CF4as a reactive gas, was employed in patterning deposited Ta2O5. These TFT's have exhibited p-channel depletion-mode characteristics with a threshold voltage of 2.5 V and a transconductance of 70 µS at Vg= - 2 V. An on-off current ratio exceeding 10⁵has been obtained.     

Quadruply self-aligned stacked high-capacitance RAM using Ta2O5high-density VLSI dynamic memory

A new one-transistor, one-capacitor RAM cell structure called a Quadruply Self-Aligned Stacked High Capacitance (QSA SHC) RAM is proposed as a basic cell for a future one-million-bit VLSI memory. This cell consists of a QSA MOSFET and a Ta2O5capacitor stacked on it. By this cell, the ultimate cell area3F times 2Fcan be realized with sufficient operating margin. Here,Fis the minimum feature size. The basic cell was fabricated and its operation was experimentally verified. The leakage current of Ta2O5film was small enough for the storage capacitor dielectric. Using a3F times 4Fcell and a4Fpitch sense amplifier, a one-million-bit memory was designed with a 2-µm rule. A cell size of 6.5 × 8 µm², and a chip size of 9.2 × 9.5 mm²were obtained. The access time, neglecting the RC time constant of the word line, was estimated to be about 170 ns. Based on this design, it is argued that a future one-million-bit memory can be realized by QSA SHC technology with a 2-1-µm process. The mask set of the 1-Mbit RAM was actually fabricated by an electron-beam mask maker. A photomicrograph of the 1-Mbit RAM chip patterned by the mask set is shown. This chip was patterned not to get an operating sample but to show an actual chip image of the future 1- Mbit RAM. The area of each circuit block including storage array can be seen in this chip image.     

CO2laser annealing of Si3N4, Nb2O5, and Ta2O5thin-film optical waveguides to achieve scattering loss reduction

Significant reductions in the optical scattering losses of Si3N4, Nb2O5, and Ta2O5waveguides fabricated on SiO2/Si substrates have been measured following CO2laser annealing. The largest improvements were observed for Si3N4waveguides, where waveguide attenuation values of about 6.0 dB/cm before laser annealing were reduced to as low as 0.1 dB/cm afterwards. An improvement of more than an order of magnitude was obtained for a Nb2O5waveguide upon laser annealing, the attenuation coefficient decreasing from 7.4 to 0.6 dB/cm. In the case of one Nb2O5waveguide no improvement was obtained upon laser annealing. The attenuation coefficient of a reactively sputtered Ta2O5waveguide was found to decrease from 1.3 dB/cm before laser annealing to 0.4 dB/cm afterwards. In the case of a thermally oxidized Ta2O5waveguide a small initial improvement in waveguide attenuation was followed by degradation upon further laser annealing.     

A high-performance monolithic IF amplifier incorporating electronic gain control

A direct-coupled monolithic IF amplifier that incorporates an active gain control stage and exhibits a power gain of 50 dB and an AGC range of 60 dB at 50 MHz is described. This circuit has negligible change in either input or output admittance, and has excellent signal linearity over the full range of gain control. Experimental and theoretical analyses are made of the large signal response, stability, available gain, and noise behavior of the circuit. An application to color television is discussed in which the functions of the 45-MHz IF amplifier and the dc-AGC circuitry are fabricated on a single die.     

Switching in Nb—Nb2O6—Nb devices with doped Nb2O5amorphous films

Switching properties of Nb-Nb2O5-Nb devices with doped Nb2O5amorphous films were studied as a function of applied voltage and temperature. A continuous recording of the switching process made possible the determination of switching parameters as a function of small voltage increments. Using this technique, it is found that switching occurs within 2.5 mV with a delay time > 1 ms. A switching device of this type can support an input power of ∼1 W.     

Bistable switching and conduction mechanisms in Nb-Nb2O5-Bi junctions

Bistable switching and conduction in niobium-niobium oxide-bismuth devices has been investigated. A number of these devices were found to be stable for more than 10⁶switching cycles and a limited number for more than 10⁹cycles. Upper bounds of 1 and 20 µs for switching from high to low and low to high resistance states, respectively, were observed. Three distinct types of conduction mechanisms are observed in an unformed device. These are the following: 1) the space-charge-limited current flow at high temperatures and low voltages; 2) Poole-Frenkel process at low temperatures and high voltages; and 3) field-assisted tunneling from traps at very low temperatures and high voltages. Conduction in the switching states is found to occur in a singular spot of approximately 2 µ²in area, created while forming. In the high-resistance state an activated process similar to Schottky mechanism seems to be responsible for electrical conduction. The low-resistance state increases very slightly in value on cooling from 300 to 1.6 K, has a small negative resistance "kink" in theI-Vcurves at about 0.3 V, and exhibits near ohomic behavior and "power law" behavior below and above the kink, respectively.     

A high performance monolithic In0.53Ga0.47Asvoltage-tunable transimpedance amplifier

The fabrication and performance of the first monolithically integrated In_0.53Ga_0.47As JFET voltage-tunable transimpedance amplifier for use in InP-based optoelectronic integrated circuits are reported. A narrow-gate transistor is used as an active feedback resistor. The two-stage voltage amplifier has a voltage gain of 10.7 and a bandwidth of 350 MHz. The closed-loop transimpedance of the amplifier is tunable from 10 to 24 kΩ by controlling the gate bias of the feedback transistor     

Growth of Ba2NaNb5O15single crystals for optical applications

The items discussed are: developments leading to the efficient nonlinear optical materials K3Li2Nb5O15and Ba2NaNb5O15; the relation of the stability to visible radiation shown by these materials to their, respectively, "completely filled" and "filled" tetragonal tungsten-bronze-like structures; a comparison of their physical properties to those of LiNbO3; the techniques and problems of growing optically satisfactory single crystals of Ba2NaNb5O15by pulling from the melt; processing required to obtain single domain sections and eliminate microtwinning; and the effects of excess Ba, Na, or Nb in the melt and the effects of substitutions by homologous cations.     

Low-threshold, transversely excited NdP5O14laser

We have measured the room-temperature lasing behavior of NdP5OI4(NdPP) transverselypumped at 058-wm wavelength by a CW dye laser in an excitation geometrysimulatingthat of an LED or laser diode. For acrystal 760 Nm long, the lowest transversethreshold was 4 mW. From thisthresholdandatheoreticalrelationshipbetween excitation efficiency andpump wavelength, we predict that a threshold of approximately 8.5 mW should be possible for excitation by an edge-emitting 0.8-wm wavelength LED. Usingthin NdP P samples with reflecting back surfaces for better excitation efficiency should lower this threshold by -60 percent, andgiveminimumoptical-to-optical con- version efficiencies of - 3.5 percent.     

A complete monolithic sample/hold amplifier

A monolithic sample/hold amplifier is described which includes the holding capacitor on the chip. System design considerations and tradeoffs are discussed, as well as the circuit design details. High performance is achieved by the use of a process which produces bipolar transistors and p-channel silicon-gate FET's (SIGFET's) on the same chip. Performance characteristics obtained include an acquisition time of 10 /spl mu/s (20-V step), an aperture delay time of 80 ns, and a droop rate of 30 mV/s.     

Second-harmonic generation in KB5O8· 4H2O

Theoretical calculations on the nonlinear crystal potassium pentaborate tetrahydrate (PPT) indicate that frequency doubling may be achieved over a wide spectral region of fundamental wavelengths (434 to >700 nm) using a single crystal cut. To test these results, second-harmonic generation of the ruby laser and the argon laser was investigated.     

Small-signal gain of a CO2laser amplifier utilizing a white optical reflector design

A small-signal gain of 39 dB in a nonresonant multi-path CO2laser amplifier with a discharge length of 65 cm is reported. The multipath system employed is a modified White optical reflector design. An unsaturated gain of 39 dB was observed for signals smaller than 10^-5watt. No noise component, due to the amplifier, was detected for signals as small as5 times 10^{-8}watt.     

Internal photoemission in Ag-Al2O3-Al junctions

We report a detailed study of the magnitude of the photon-induced current in Ag-Al2O3-Al metal-oxide-metal junctions as a function of photon energy and angle of incident radiation. Experimental observations and a theory based on vacuum photoemission are found to be in good agreement. Fast risetimes (lsim50ns) and linearity of the photocurrent with respect to incident power up to at least 10 kW/cm²are also reported.     

Radiation resistance of Al2O3MOS devices

Integrated circuits employing MOS devices will play a vital role in tomorrow's civilian and military electronics if their degradation in a radiation environment can be eliminated. One possible approach toward alleviating radiation effects in MOS devices is to use a material with a defect structure that does not allow predominant trapping of either holes or electrons as a gate insulator. This has been done by constructing MOS devices with plasma-grown aluminum oxide. The Al2O3films are formed by first depositing aluminum on freshly cleaned and properly prepared silicon wafers. Subsequently this aluminum is oxidized in an oxygen plasma and device fabrication is then completed. The devices have excellent characteristics and stability, and their fabrication is not restricted by the conditions of the ultra-clean procedures necessary for SiO2-Si devices. Exposure to 1-MeV electron bombardment at various fluence levels and bombardment-bias conditions shows that these structures possess remarkable radiation resistance. Up to a fluence of 1 × 10¹³e/cm², under positive or negative bias, no oxide charge buildup or interface state generation is detectable. Above that fluence, only small shifts are observed. This indicates that an order of magnitude improvement in device hardening can be achieved by the use of this material.     

Photoresponses in In2O3transparent gate MOS capacitors

In this paper electrical and photoelectronic properties of sputtered In2O3films including 5 wt % SnO2and transparent gate MOS capacitors employing this film were discussed. In order to improve the characteristics of the sputtered films and to recover the radiation damage generated during the sputtering process, high-temperature annealing of the film in nitrogen was important. In the present experiment, the best post-annealing temperature was about 850°C, and the minimum resistivity ρ and the interface-state density Nsswhich resulted from this annealing were 1.1 × 10^-3Ω . cm and 6.5 × 10¹⁰cm^-2. eV^-1, respectively. The dark current was comparable to that of conventional Al-gate MOS capacitors. Moreover, it became clear that the recombination loss of photogenerated carriers due to the interface states caused the degradation of the spectral response in the short wavelength range, when the surface of the MOS substrate was maintained in the vicinity of mid-gap potential. However, the transparent gate MOS capacitors biased in weak or strong inversion could be usable as high-sensitivity, photosensors in the blue region of the spectrum, because the interface states could not act as effective recombination centers for these bias conditions.     

A wide-band high-voltage monolithic amplifier

A monolithic amplifier capable of 80-V swing and 1.7-V/NS slew rate has been fabricated using standard integrated circuit techniques. The amplifier is intended for capacitive loads such as in electrostatic deflection applications. The totem-pole technique is combined with active feedback to produce this large voltage swing without excessive power consumption. A new output circuit linked with a floating current source is used to supply large accurate positive and negative charging currents over a large dynamic range. The amplifier voltage range is extendable by increasing the degree of stacking in the totem-pole arrangement.     

A low-distortion monolithic wide-band amplifier

A wide-band monolithic amplifier is described which realizes 20-dB gain and 250-MHz bandwidth using an 800-MHz integrated-circuit process. At 0-dBm signal levels, second- and third-order inter-modulation distortion levels are below -55 and -42 dB, respectively, across the band. Terminal impedances are matched to 75 /spl Omega/ with VSWR better than 1.7. Both circuit and process design are described as well as computer optimization of circuit performance.     

A millimeter-wave monolithic grid amplifier

A 36-element monolithic grid amplifier has been fabricated. The peak gain is 5 dB at 40.8 GHz with a 3-dB bandwidth of 1.4 GHz. The active elements are pairs of heterojunction-bipolar-transistor's (HBT's). The individual transistors in the grid have a maximum oscillation frequency,f _max , of 100 GHz. The grid includes base stabilizing capacitors which result in a highly stable grid. This is the first report of a successful monolithic grid amplifier.