OPEL's new and patented semiconductor fabrication process, POET (Planar Optoelectronic Technology), is based on a unique Group III-V materials structure. The POET materials structure is a four-layer, PNPN, electrical structure having two sets of independent quantum wells, and is specifically designed to support both active optical elements (laser, photoreceiver), and high-speed complementary HEMT and HBT transistors. This materials structure is realized as an epitaxy grown on a semi-insulating GaAs wafer. The processing of these wafers into products is done using a series of steps similar to those used in silicon processing, and is scalable to deep submicron feature sizes. POET device yield will thus be similar to that of silicon, much higher than that characteristic of many current III-V processes. This gives OPEL a technology basis that is uniquely powerful, that is economical to produce, and that is extensible in generations. Capitalizing on POET capabilities, OPEL will offer products into the communications, optoelectronic, RF/wireless, sensor, and imaging markets.
POET is a uniquely-powerful mixed-signal process, integrating high-performance analog and digital electronics with high-performance active optical elements. OPEL ICs integrate a dense mix of active optical elements and optical waveguides together with logic and mixed-signal elements on a single chip, thus manufactured in one serial process. The key elements integrated in the process, all simultaneously available for design, are: The Optical Thyristor (OT), Complementary HEMT and HBT devices, and Dielectric Isolation.
Optical Thyristor:
The Optical Thyristor is a multiple-use device, and is the backbone of POET. The OT is a four-terminal device having both optical and electrical inputs and optical and electrical outputs. Depending on application and design, an OT can be a laser, optical amplifier, or photoreceiver, or may execute various electrical operations. An additional aspect of the POET OT is a process step that allows for emission and reception of light in-plane, parallel to the chip surface. Lasers and photoreceivers may either be designed with vertical emission, or use this step to have in-plane emission. This step allows on-chip optical interconnections, and also supports a low-cost multiple-fiber attachment system that OPEL has designed.
Various modifications of the basic POET epitaxial structure will support emission or reception at wavelengths of 980, 1310, or 1550 nm. OPEL's innovative structure and fabrication also provides detection and emission from the 3 to 20 m m band via the unique attributes of its quantum well structure.
OT Lasers:
POET lasers are of a third-generation fabrication using an implant confinement technique and have improved efficiency and reliability over the proton-confined and oxide-confined devices currently available. Either vertical emission, or in-plane emission may be employed, depending on design needs. When the in-plane feature is employed, vertical cavity lasers are formed in stripe geometries, and have end emission. Such vertical cavity traveling wave lasers have ratios of peripheral length to active area much higher than conventional circular VCSELs, dissipating power more readily, and resulting in higher reliability components of longer life. All POET lasers can be driven by a logic voltage signal, further lowering power requirements and increasing efficiency. Wall plug efficiency will exceed 50%.
OT Photoreceivers:
As photoreceivers, OTs have high sensitivity, are self-contained, and do not require TIAs (TransImpedance Amplifiers) to produce usable outputs. Incident light of adequate intensity will produce a direct electrical logic signal. Analog amplification and thresholding is not required in OPEL OT photoreceivers. All optical OT structures can be made selectively as lasers or photoreceivers, further adding to POET IC flexibility. The in-plane emission feature of POET allows easy connection to on-chip passive waveguides. This waveguide technology features enlarged waveguide apertures to facilitate ease of coupling to single mode fibers with very low device insertion loss. This feature is also key to OPEL's low-cost multiple fiber attachment technology via waveguides. OPEL has devised a packaging technology to match this horizontal I/O coupling, further maintaining the cost-effective approach.
OT Electrical Applications:
The optical thyristor can also act as an electronic device in storage, logic and millimeter-wave oscillator applications. OTs can form single-device static RAM cells, and can be designed for bistable logic uses (flip-flops). An OT with an optical cavity forms a uniquely low-noise voltage controlled oscillator. OTs acting as comparators are the heart of our ultra high speed A/D converter designs.
POET Transistors:
POET transistors suit a wide range of high-performance needs. Electronic designs can be performed using an arbitrary mix of complementary Heterojunction Bipolar Transistors (HBT), or unique complementary High Electron Mobility Transistors (CHEMT).
Complementary HEMT Transistors:
The POET process offers both p-channel and n-channel HEMT devices with complementary threshold voltages. These devices are usable in both low-noise RF applications and in very high-speed low power logic. Complementary HEMT logic has a speed-power ratio similar to that of silicon CMOS, owing to the higher mobility of the HEMT structure, and can form very low power logic running at speeds to over 100 GHz. This allows the integration of dense logic circuitry with low power, high speed, and small size. This allows any mix of analog circuits and logic circuits to be included in an IC, design, when such integration can improve system performance.
Complementary HBT Transistors:
Complementary HBT devices operate in various analog and RF applications into the Terahertz range.
Dielectric Isolation:
One of the POET design elements supporting effective optoelectronic integration is its high-quality dielectric isolation. DI "islands" are formed by deep trench etch through the entire epitaxial structure into the substrate. Under each active "island" is a layer of oxide produced in the process step in which the lower mirrors are formed. The electrical coupling path between such dielectric "islands" is through the oxide of one region, through a semi-insulating substrate, then through the oxide of another island. This DI produces a much higher isolation than the reverse-junction and deep trench isolations of silicon, and is essentially a free product of the POET process.
This high-quality isolation is a principal factor in our being able to produce mixed -signal designs such as optoelectronic transceivers. Without this isolation, a typical implementation problem is a resulting crosstalk between the more sensitive receive section and the higher-powered transmit section. POET DI greatly reduces such a problem and allows OPEL to produce such integrated designs.
POET-Based IC designs:
OPEL integrated circuits contain combinations of optical and electronic devices designed to meet specific application, and are manufactured in the POET process. Designs are all fabricated using the same POET process, then tested, optically and electrically, as one single manufactured unit, minimizing cost. All of the elements of OT lasers, OT photoreceivers, OT logic circuits, optical interconnect, HBT transistors, HEMT transistors and dielectric isolation are useable in any number and combination, as the design requires, just as in any other semiconductor process.
This makes POET far and away the most powerful, versatile optoelectronic mixed signal process in existence!
