Donald Sawdai

Demonstration of a 311-GHz Fundamental Oscillator Using InP HBT Technology

In this paper, a sub-millimeter-wave HBT oscillator is reported. The oscillator uses a single-emitter 0.3 m15 m InP HBT device with maximum frequency of oscillation greater than 500 GHz. The passive components of the oscillator are realized in a two metal process with benzocyclobutene used as the primary transmission line dielectric. The oscillator is implemented in a common base topology due to its inherent instability. The design includes an on-chip resonator, output matching circuitry, and injection locking port. A free-running frequency of 311.6 GHz has been measured by down-converting the signal. Additionally, injection locking has been successfully demonstrated with up to 17.8 dB of injection-locking gain. This is the first fundamental HBT oscillator operating above 300 GHz.

Enhanced transmission line model structures for accurate resistance evaluation of small-size contacts and for more reliable fabrication

Two new transmission line model (TLM) techniques are presented, The first structure, LT-TLM, provides very accurate determination of the transfer length LT (within 5%) and the contact resistivity /spl rho//sub C/ (within 12%) of lateral contacts, as compared to typical errors of 30% and 50%, respectively, for conventional TLM patterns, accurate determination of these quantities is important for the optimal design of small lateral contacts in high-performance devices, such as heterojunction bipolar transistors (HBTs). The second structure, a modified concentric TLM pattern, provides the same results as conventional TLM patterns; however, they do not require mesa isolation, and they can be fabricated extremely reliably. In contrast, conventional concentric TLM patterns are often shorted together or distorted by lift-off metallization processes. Both theoretical analysis and experimental verification with analysis of the accuracy of the extracted data is presented for each technique, demonstrating the advantages of these approaches.

Demonstration of 184 and 255-GHz Amplifiers Using InP HBT Technology

In this letter, 184 and 255 GHz single-stage heterojunction bipolar transistor (HBT) amplifiers are reported. Each amplifier uses a single-emitter 0.4 ¿m 15 ¿m InP HBT device with maximum frequency of oscillation (fmax) greater than 500 GHz and of 200 GHz. The 183 GHz single-stage amplifier has demonstrated gain of 4.3 ± 0.4 dB for all sites on the wafer. The 255 GHz amplifier has measured gain of 3.5d B and demonstrates the highest frequency measured HBT amplifier gain reported to date. Both amplifiers show excellent agreement with original simulation.

Measurements of the InGaAs hole impact ionization coefficient in InAlAs/InGaAs pnp HBTs

The hole multiplication factor in pnp InAlAs/InGaAs single heterojunction bipolar transistors (HBTs) has been measured as a function of the base-collector bias. The hole impact ionization coefficient /spl beta//sub p/ has been estimated taking into account the Early effect, I/sub CBO/, and thermal effects. Numerical corrections for dead space were made. The importance of considering second order effects is highlighted, showing that rough approximations can lead to an overestimation of the coefficient /spl beta//sub p/. At low electric fields, the extracted coefficient agrees with the most recent photomultiplication measurements available in the literature. At high electric fields, hole impact ionization coefficient is estimated up to values previously not reported in the literature (/spl beta//sub p//spl ap/10/sup 4/ cm/sup -1/).

Push-pull circuits using n-p-n and p-n-p InP-based HBT's for power amplification

P-n-p heterojunction bipolar transistors (HBTs) have been combined with n-p-n HBTs in a push-pull amplifier in order to obtain improved linearity characteristics. Simulations of common-collector push-pull amplifiers demonstrate an improvement of 14 dB in second harmonic content at the onset of power saturation under class-B operation. Further improvement of 14 dB in the third harmonic content is shown by moving to class-AB operation at an expense of 4% decreased efficiency. A common-emitter push-pull amplifier was fabricated using both n-p-n and p-n-p HBTs with external matching and couplers. Testing of the circuit under class-AB conditions showed better third-order intermodulation (by /spl sim/9 dBc) and smaller second harmonic content (by /spl sim/11 dBc) compared with n-p-n HBTs alone. While the second harmonics were shown to combine destructively in the push-pull amplifier, total cancellation of the second harmonic was prevented by the wide difference in linearity characteristics of the n-p-n and p-n-p HBTs. In addition, the circuit produced over 2 dBm more output power than the n-p n HBT alone at 1 dB of gain compression.

Power performance of InP-based single and double heterojunction bipolar transistors

The microwave and power performance of fabricated InP-based single and double heterojunction bipolar transistors (HBTs) is presented. The single heterojunction bipolar transistors (SHBTs), which had a 5000 /spl Aring/ InGaAs collector, had BV/sub CEO/ of 7.2 V and J/sub Cmax/ of 2/spl times/10/sup 5/ A/cm/sup 2/. The resulting HBTs with 2/spl times/10 /spl mu/m/sup 2/ emitters produced up to 1.1 mW//spl mu/m2 at 8 GHz with efficiencies over 30%. Double heterojunction bipolar transistors (DHBTs) with a 3000-/spl Aring/ InP collector had a BV/sub CEO/ of 9 V and J/sub c max/ of 1.1/spl times/10/sup 5/ A/cm/sup 2/, resulting in power densities up to 1.9 mW//spl mu/m/sup 2/ at 8 GHz and a peak efficiency of 46%. Similar DHBTs with a 6000 /spl Aring/ InP collector had a higher BV/sub CEO/ of 18 V, but the J/sub c max/ decreased to 0.4/spl times/10/sup 5/ A/cm/sup 2/ due to current blocking at the base-collector junction. Although the 6000 /spl Aring/ InP collector provided higher f/sub max/ and gain than the 3000 /spl Aring/ collector, the lower J/sub c max/ reduced its maximum power density below that of the SHBT wafer. The impact on power performance of various device characteristics, such as knee voltage, breakdown voltage, and maximum current density, are analyzed and discussed.

Power performance of InGaAs/InP single HBTs

Typically, the microwave power characteristics of InP/InGaAs SHBTs have not been addressed due to their relatively inferior DC characteristics when compared to DHBTs, which implies early breakdown and thus limited power performance. On the other hand, SHBTs are very attractive for higher frequency applications due to the absence of the heterojunction spike at the base-collector (B-C) interface. Moreover, the homojunction B-C structure offers direct compatibility for HBT integration with PIN diodes, since the latter can be realized by using the B-C-subcollector region. Such integration is needed not only for OEICs but also for MMICs with switching capabilities. This paper reports for the first time a systematic investigation of InP-based SHBT characteristics and demonstrates their suitability for power applications.

Characterization and measurement of non-linear temperature rise and thermal resistance in InP heterojunction bipolar transistors

We present a method of measurement and characterization of the differential thermal resistance and non-linear temperature rise for small GaAs and InP heterojunction bipolar transistors. It is shown that nonlinear thermal behavior of the transistor can be completely described by the zero power thermal resistance and linear temperature coefficient, and that for small devices the zero power thermal resistance approximately scales with emitter area and that this scaling is more favorable for InP HBTs when compared to GaAs HBTs.

Power performance of PNP InAlAs/InGaAs HBTs

Recently, small-signal microwave performance has been reported for PNP InAlAs/InGaAs HBTs. While power performance of PNP AlGaAs/GaAs HBTs has been demonstrated, nothing has been reported on power performance of PNP HBTs in the InP material system. In this work, InAlAs/InGaAs PNP HBTs were fabricated and subsequently characterized under large signal conditions at X-band to determine their suitability for high-frequency power applications. PNP HBTs demonstrated f/sub T/ and f/sub max/ as high as 13 and 35 GHz, respectively. Power performance at 10 GHz was comparable to InP-based NPN single HBTs, providing up to 10 dB of gain, 0.49 mW//spl mu//sup 2/ of output power, and 24% power-added efficiency. Analysis of these HBTs suggests further design and epilayer optimizations for increased power performance.

Sub-Micrometer InP/InGaAs Heterojunction Bipolar Transistors with fT = 400 GHz and fmax > 500 GHz

We report InP-based double heterojunction bipolar transistors (DHBTs) with emitter widths of 0.25 mum and RF performance of fT = 400 GHz and fmax >500 GHz. The HBT structure consists of an InP emitter with an abrupt emitter-base interface, a 300 compositionally graded InGaAs base region, and a 1200Aring collector. The scaled devices reported here have been integrated with a planar, multi-level interconnect process to produce static divide-by-2 circuits with maximum input frequencies greater than 150 GHz and small DDS circuits with output fclock up to 21 GHz. We believe that the device and interconnect technology reported here represents a combination of performance and integration suitable for future digital and mixed-signal applications while maintaining the manufacturability required for large circuit yield