Ted Johansson

Self-heating effects in a BiCMOS on SOI technology for RFIC applications

Self-heating in a 0.25 /spl mu/m BiCMOS technology with different isolation structures, including shallow and deep trenches on bulk and silicon-on-insulator (SOI) substrates, is characterized experimentally. Thermal resistance values for single- and multifinger emitter devices are extracted and compared to results obtained from two-dimensional, fully coupled electrothermal simulations. The difference in thermal resistance between the investigated isolation structures becomes more important for transistors with a small aspect ratio, i.e., short emitter length. The influence of thermal boundary conditions, including the substrate thermal resistance, the thermal resistance of the first metallization/via layer, and the simulation structure width is investigated. In the device with full dielectric isolation-deep polysilicon-filled trenches on an SOI substrate-accurate modeling of the heat flow in the metallization is found to be crucial. Furthermore, the simulated structure must be made wide enough to account for the large heat flow in the lateral direction.

Implanted collector profile optimization in a SiGe HBT process

Abstract Optimization of implanted collector doping profiles for a high-speed, low-voltage SiGe HBT process has been investigated experimentally and by device simulations. A low-energy antimony implantation has been combined with a standard selectively implanted collector using phosphorous, to achieve improved control of the collector doping profile. The simulations indicate that the narrow n-type doping peak formed by the antimony implantation allows the cut-off frequency f T to be increased without degrading the collector emitter breakdown voltage BV CEO . The fabricated devices demonstrate a highest f T of 60 GHz. Depending on the collector profile BV CEO values between 1.5 and 2 V were obtained.

A novel approach to 3-D modeling of packaged RF power transistors

Packaged radio frequency (RF) power transistors with internal matching networks for use at 1.8-2 GHz in cellular base stations have been modeled using three-dimensional (3-D) electromagnetic-field simulators and SPICE. A method for extracting the actual internal 3-D geometries applying scanning electron microscope micrographs and software running in Java was developed. The results show good correlation between measured and simulated data in the 0.1-6 GHz interval studied. The importance of the mutual coupling and capacitance contributions from the package was demonstrated for different frequency domains. The described approach provides an interesting and promising method for modeling the interior parts of RF power transistors or other complex package structures, where geometry and coupling play a far greater role than for integrated-circuit packages.

Characterization of LaRhO3 perovskites for dry (CO2) reforming of methane (DRM)

This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H2-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)3. The CH4-TPR data show qualitatively similar results as H2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H2-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O2/He up to 500°C and a second H2-TPR (also up to 950°C) was conducted. This second H2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H2 formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H2-TPR results. TPSR, after a H2-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.

Characterization of LaRhO 3 perovskites for dry (CO 2 ) reforming of methane (DRM)

This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H2-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)3. The CH4-TPR data show qualitatively similar results as H2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H2-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O2/He up to 500°C and a second H2-TPR (also up to 950°C) was conducted. This second H2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H2 formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H2-TPR results. TPSR, after a H2-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.

Characterization of perovskite LaRhO3 for dry (CO2) reforming of methane (DRM)

This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H2-TPR of the fresh calcined catalyst showed a shoulder at 342°C and a broad peak at 448°C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)3. The CH4-TPR data show qualitatively similar results as H2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H2-TPR up to 950°C, the same batch of catalyst was oxidized by flowing 5 vol. % O2/He up to 500°C and a second H2-TPR (also up to 950°C) was conducted. This second H2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163°C in the second H2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500°C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H2 formation starting at 400°C, with complete consumption of the reactants at 650°C. The uneven consumption of reactants between 400°C and 650°C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H2-TPR results. TPSR, after a H2-TPR up to 950°C, showed that the dry reforming reaction did not light off until 570°C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950°C H2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.

Formation of a buried collector layer in RF-bipolar devices by ion implantation

High-dose implantation of arsenic (As) buried collector layer formation for bipolar/BiCMOS processes has been studied. Wafers with and without screen oxide were subjected to high-dose implants with different energies. Some wafers were given a low-temperature anneal before XTEM and SIMS analyses. Defects observed after As implants of 6E15cm^-^2 through screen oxide after low-temperature anneal were annihilated at the subsequent high-temperature steps, but the direct implant of As into the silicon is preferred since fewer defects are generated and there is no knock-on of oxygen into the material. Fabricated devices showed excellent electrical performance. However, the upper limit (dose and/or energy) at which perfect recrystallization does no longer occur has not been defined and the process limit is consequently not established.

Feasibility study of 25 V SiGe RF-power transistors for cellular base station output amplifiers

Abstract For 2+ GHz-bandwidth applications, the commonly used bipolar Si RF-power transistors in the output amplifiers in cellular base stations for mobile communications are pushed to the limit of performance. The objective of this work was to study the feasibility of using SiGe/Si grown on pre-processed Si wafers for power-HBTs operating at 25 V for improved performance. The large size HBT devices (2×0.1 mm 2 ) were processed using an existing 100 mm poly-Si emitter RF power BJT technology with Au metallization and some necessary modified steps for SiGe implementation. The base layers with designed Ge and B profiles were deposited either by MBE or CVD. The devices showed very high BV cbo (>80 V) with very low leakage currents. The current gain was very stable over a wide I C range, and weakly influenced by the environmental temperature. At 2 GHz, the CW output power of 20 W (at 25 V) was obtained with an efficiency of 68% in class AB operation. The long-term temperature stability was excellent. SiGe RF power-HBTs could be operated at full output power for an extended time without any external temperature bias compensation, which is virtually impossible with conventional Si-BJTs.

3D characterization of RF power transistors

3D electromagnetic simulations and SPICE were used to model the influence of wire geometry, internal matching networks and package on the characteristics of high-power RF transistors for cellular base stations. A method for extracting the actual internal 3D geometries by applying SEM micrographs and Java software was developed. Measured transistor data was correlated with simulated data, and the importance of the contributing elements and the mutual coupling of the bond wires was demonstrated.