Paul M. Enquist

Monolithic integration of complementary HBTs by selective MOVPE

The monolithic integration of n-p-n and p-n-p heterojunction bipolar transistors (HBTs) through the use of selective metal organic vapor phase epitaxial regrowth is discussed. This was accomplished by masking, patterning, and etching a p-n-p HBT wafer and then selectively regrowing an n-p-n structure in the etched areas. The selective epitaxial regrowth did not degrade the current gain of the p-n-p structure. Several complementary amplifier circuits were fabricated and tested successfully, demonstrating the feasibility of a monolithic complementary HBT technology.<<ETX>>

Low emitter resistance GaAs based HBT's without InGaAs caps

Low emitter resistance is demonstrated for AlGaAs/GaAs heterojunction bipolar transistors using Pd/Ge contacts on a GaAs contact layer. The contact resistivity to 2-10/spl times/10/sup 18/ cm/sup -3/ n-type GaAs is 4-1/spl times/10/sup -7/ /spl Omega/-cm/sup 2/. These are comparable to contact resistivities obtained with non-alloyed contacts on InGaAs layers. The non-spiking Pd/Ge contact demonstrates thermal stability and area independent resistivity suitable for scaled devices. The substitution of Pd/Ge for AuGe/Ni GaAs emitter and collector contacts reduced by an order of magnitude the emitter-base offset voltage at high current densities and increased f/sub t/ by more than 15% with significantly improved uniformity for devices with 2 and 2.6 /spl mu/m wide emitters having lengths two, four and six times the width.<<ETX>>

Pnp HBT with 66 GHz f/sub max/

The total emitter to collector delay for a Pnp AlGaAs/GaAs HBT has been reduced to 4.8 ps by employing a thin base (325 /spl Aring/) and collector (2300 /spl Aring/). Simultaneously, a low base sheet resistance of 170 ohms/square was achieved with tellurium doping. A higher collector doping than is typically used permitted operation at collector current densities in excess of 5/spl times/10/sup 4/ A/cm/sup 2/. A single emitter (2/spl times/4 /spl mu/m/sup 2/) and a single base contact device topology has an f/sub t/ and f/sub max/ of 33 and 66 GHz, respectively.<<ETX>>

Self-aligned AlGaAs/GaAs HBT with selectively regrown OMVPE emitter

A self-aligned HBT mesa fabrication process utilizing selective organometallic vapor phase epitaxy (OMVPE) is reported whereby the extrinsic base has been made considerably thicker than the intrinsic base, thus avoiding the conventional tradeoff between base resistance and base transit time. This technique also simplifies processing by eliminating the need for emitter isolation by etching or ion implantation prior to base metallization. Application of this process to AlGaAs/GaAs N-p-n HBTs has yielded an intrinsic to extrinsic base sheet resistance ratio of 1.5, an f/sub T/ of 22 GHz, and an f/sub max/ of 55 GHz.<<ETX>>

Complementary AlGaAs/GaAs HBT I/sup 2/L (CHI/sup 2/L) technology

The monolithic integration of non-self-aligned AlGaAs/GaAs N-p-n and P-n-p HBTs with selective organometallic vapor-phase epitaxy (OMVPE) has been utilized to demonstrate a low-power high-speed integrated injection logic (I/sup 2/L) technology. Seventeen-stage ring oscillators with a logic swing of 0.7 V exhibited a delay of 65 ps per gate with power dissipation of 13 mW per gate for a speed-power product of 850 fJ. This value was in excellent agreement with SPICE simulations based on extracted device parameters which predicted a speed-power product of 840 fJ. Additional simulations predicated a 28-fJ speed-power product and more than a factor of 2 reduction in gate delay with improved epitaxial design and use of submicrometer emitters and self-aligned processing.<<ETX>>

Millimeter-wave AlGaAs/GaAs p-n-p HBT

The total emitter-to-collector delay for a p-n-p AlGaAs/GaAs heterojunction bipolar transistor (HBT) has been reduced to 5.7 ps by extending the cutoff frequency for these devices to the millimeter-wave range. A total charging delay of 1.2 ps was obtained by a lightly doped emitter and by reducing the collector resistance. Low transit delays totaling 4.5 ps were achieved with a thin (440 AA) uniformly doped base and a thin (2800 AA) collector. The reduction in these delays permitted a non-self-aligned (1- mu m emitter mesa/base contact separation) device with two emitters (2.6*10 mu m/sup 2/ each) and a single base contact to exhibit an f/sub t/ of 28 GHz.<<ETX>>

Experimental values for the hole diffusion coefficient and collector transit velocity in P-n-p AlGaAs/GaAs HBTs

The diffusion coefficient (D/sub h/) and a value for the collector velocity (v/sub h/) of holes in AlGaAs/GaAs P-n-p HBTs (heterojunction bipolar transistors) were obtained from high-frequency measurements on structures with different base and collector widths. Quantities for D/sub h/ and v/sub h/ of 5.6 cm/sup 2//s and 5.5*10/sup 6/ cm/s, respectively, were obtained by plotting the total emitter-collector delay versus inverse emitter current and extrapolating the data to infinite emitter current to obtain the base and collector transit delays. An f/sub t/ and f/sub max/ as high as 15 and 29 GHz, respectively, were obtained for non-self-aligned (1- mu m emitter mesa/base contact separation) devices with a 2.6- mu m*10- mu m emitter.<<ETX>>

Performance evaluation of heterojunction bipolar transistors designed for high optical gain

This paper evaluates the performance of thin base Npn heterojunction bipolar transistors designed for high optical gain in the base while biased in the active regime. Pisces/Blaze simulations indicate that injected carrier concentrations exceeding 10/sup 19/ cm/sup -3/ can be achieved resulting in an estimated optical gain /spl sim/3000 cm/sup -1/. Furthermore, a very large increase in differential base electron concentration with emitter current yields a high modulation depth with no insertion loss but low f/sub T/. Estimated performance of this device in a microwave fiber optic link application is given.

Monolithically integrated SQW laser and HBT laser driver via selective OMVPE regrowth

An AlGaAs/GaAs nan heterojunction bipolar transistor (HBT) laser driver circuit and a pseudomorphic InGaAs/GaAs/AlGaAs graded index single-quantum-well (SQW) laser have been laterally integrated to maintain surface planarity using selective organometallic vapor-phase epitaxy (OMVPE) regrowth of the HBT. The self-aligned HBTs exhibit a DC current gain of 30 and an f/sub t/ (f/sub max/) of 45(60) GHz. The 980-nm lasers exhibit room-temperature threshold current densities as low as 420

Multi-level interconnects for heterojunction bipolar transistor integrated circuit technologies

Heterojunction bipolar transistors (HBTs) are mesa structures which present difficult planarization problems in integrated circuit fabrication. The authors report a multilevel metal interconnect technology using Benzocyclobutene (BCB) to implement high-speed, low-power photoreceivers based on InGaAs/InP HBTs. Processes for patterning and dry etching BCB to achieve smooth via holes with sloped sidewalls are presented. Excellent planarization of 1.9 {micro}m mesa topographies on InGaAs/InP device structures is demonstrated using scanning electron microscopy (SEM). Additionally, SEM cross sections of both the multi-level metal interconnect via holes and the base emitter via holes required in the HBT IC process are presented. All via holes exhibit sloped sidewalls with slopes of 0.4 {micro}m/{micro}m to 2 {micro}m/{micro}m which are needed to realize a robust interconnect process. Specific contact resistances of the interconnects are found to be less than 6 {times} 10{sup {minus}8} {Omega}cm{sup 2}. Integrated circuits utilizing InGaAs/InP HBTs are fabricated to demonstrate the applicability and compatibility of the multi-level interconnect technology with integrated circuit processing.