GaAs Heterojunction Bipolar Transistor Technology Research Articles

Characterization of ALD Ta2O5, Al2O3, and Ta2O5/Al2O3 Nanolaminate as Metal-Insulator-Metal Capacitor Dielectric for GaAs HBT Technology

In order to reduce die size and increase capacity, the metal-insulator-metal (MIM) capacitor area in circuit designs fabricated using GaAs hetero-junction bipolar transistor (HBT) technology has to be reduced. This can be achieved by using a capacitor dielectric material that has a high dielectric constant or high capacitance density. In GaAs HBT technology, the MIM capacitor dielectric film is typically also required to have a high breakdown voltage (>20 V) and low leakage current. Furthermore, the deposited dielectric film has to be compatible with GaAs processing and has to be deposited at a temperature of < 300oC, due to the limited process thermal budget in the HBT technology. As a result of these requirements, there are only a few materials available for MIM capacitor dielectric application in GaAs HBT technology.In this study, 60 nm tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and Ta2O5/Al2O3 nanolaminate deposited using atomic layer deposition (ALD) have been characterized and evaluated as MIM capacitor dielectric for GaAs HBT technology. The results show that the capacitor with 60 nm of ALD Ta2O5 has the highest capacitance density (3.84x10-15 F/μm2), followed by the capacitor with 60 nm Ta2O5/Al2O3 nanolaminate, and the capacitor with 60 nm Al2O3 capacitor dielectric film with a capacitance density of 2.40x10-15 F/µm2 and 1.37x10-15 F/μm2, respectively. The calculated dielectric constant of ALD Ta2O5 and Ta2O5/Al2O3 nanolaminate is 26.1 and 16.3, respectively, while that of ALD Al2O3 is 9.3, as shown in Figure 1.Figure 2 shows the I-V characteristics of MIM capacitors with 4055 μm2 area and with 60 nm of ALD Ta2O5, Ta2O5/Al2O3 nanolaminate, and Al2O3 capacitor dielectric. As can be seen, the capacitor with Al2O3 capacitor dielectric has significantly lower leakage and higher breakdown voltage (46 V), while the capacitor with Ta2O5/Al2O3 and Ta2O5 capacitor dielectric has higher leakage current and lower breakdown voltage of 32.7 V and 22.4 V, respectively. Figure 3 shows the C-V characteristics of capacitors with the 3 ALD capacitor dielectric films. The results show that the capacitance of MIM capacitor using these three films increased marginally by 2.2% to 4.3%, when the temperature was increased from 25oC to 125oC. No significant change in capacitance density of these ALD capacitor dielectric films was observed, when the applied voltage was varied from -5 V to +5 V. Figure 1

Characterization of ALD Ta2O5, Al2O3, and Ta2O5/Al2O3 Nanolaminate as Metal-Insulator-Metal Capacitor Dielectric for GaAs HBT Technology

Tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and Ta2O5/Al2O3 nanolaminate deposited using atomic layer deposition (ALD) have been characterized and evaluated as metal-insulator-metal (MIM) capacitor dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. The results show that the capacitor with 60 nm of ALD Ta2O5 and Al2O3 capacitor dielectric films resulted in a capacitance density of 3.84x10-15 F/μm2 and 1.37x10-15 F/μm2 and a dielectric constant of 26.1 and 9.3, respectively, while the capacitor with 60 nm of ALD Ta2O5/Al2O3 nanolaminate capacitor dielectric film resulted in capacitance density of 2.40x10-15 F/μm2 and a dielectric constant of 16.3. The capacitance density of capacitor using these three films increased marginally by 2.2% to 4.3%, when the temperature was increased from 25oC to 125oC. No significant change in capacitance density of these ALD films was observed, when the applied voltage was varied from -5 V to +5 V. The leakage current density of the ALD Al2O3, Ta2O5, and Ta2O5/Al2O3 nanolaminate films at an electric field of 3 MV/cm is 2.0x10-16 A/μm2, 6.8x10-8 A/μm2, and 9.2x10-13 A/μm2, respectively. The 60 nm ALD Al2O3 film has higher breakdown voltage of 46 V, compared to the 60 nm ALD Ta2O5 film and the 60 nm Ta2O5/Al2O3 nanolaminate film, which has a breakdown voltage of 22.5 V and 32.7 V, respectively. As the temperature was increased from 25oC to 125oC, the leakage current increased and breakdown voltage decreased for all three ALD films.

Comparative study and characterization of atomic layer deposition Al2O3 films as metal-insulator-metal capacitor dielectric for GaAs hetero-junction bipolar transistor technology

Atomic layer deposition (ALD) aluminum oxide (Al2O3) films have been deposited using trimethyl aluminum (TMA) and H2O, and using TMA and H2O with O3 as precursors, and were characterized and evaluated as a metal-insulator-metal (MIM) capacitor dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. The results show that the capacitor with 60 nm of ALD Al2O3 capacitor dielectric films deposited using TMA and H2O and deposited using TMA, H2O, and O3 resulted in a capacitance density of 1.36 × 10−15–1.37 × 10−15 F/μm2, and a dielectric constant of 9.2–9.3. The capacitance density of the capacitor using these films increased by 2.3%–3.0%, when the temperature was increased from 25 to 125 °C. No significant change in capacitance density of these ALD films was observed when the applied voltage was varied from −5 to +5 V. However, the 60 nm ALD aluminum oxide film deposited using the TMA, H2O, and O3 has significantly higher breakdown voltage (46 V) compared to the ALD aluminum oxide film deposited using TMA and H2O only (38.4 V). Furthermore, the leakage current density of the ALD Al2O3 from TMA, H2O, and O3 is significantly lower compared to that of ALD Al2O3 from TMA and H2O (5.6 × 10−8 A/cm2 vs 8.9 × 10−6 A/cm2 at 5 MV/cm). As the temperature was increased from 25 to 125 °C, the breakdown voltage of both films decreased, while the leakage current marginally increased. Additionally, as the capacitor area is increased, the leakage current also increased, while no change in breakdown voltage is observed.

Analysis and Design of a Broadband Frequency Divider Using Modified Active Loads in GaAs HBT

A modified divide-by-2 regenerative frequency divider (RFD) is presented in this paper. The effects of modified active loads on the bandwidth of RFD are demonstrated and analyzed in detail by introducing the equivalent circuit using [Formula: see text] model. Using the transimpedance amplifier structure with resistive shunt–shunt feedback and shunt-peaked inductor as the active loads of the generative frequency divider, the loop bandwidth and the loop gain can be increased at higher frequencies to extend the bandwidth. Based on the theoretical analysis and design methodology, an RFD with improved active loads is designed and fabricated in 1[Formula: see text][Formula: see text]m GaAs heterojunction bipolar transistor technology with a total chip area of 0.83[Formula: see text]mm[Formula: see text][Formula: see text][Formula: see text]0.75[Formula: see text]mm. The measured phase noise at the divider output is less than [Formula: see text]110[Formula: see text]dBc/Hz with 100[Formula: see text]kHz offset and is [Formula: see text]127.6[Formula: see text]dBc/Hz with 1[Formula: see text]MHz offset. The operation frequency range is from 10 to 26[Formula: see text]GHz. The power consumption of the divider core is 166.44[Formula: see text]mW, and the frequency bandwidth is 16[Formula: see text]GHz at a supply voltage of [Formula: see text]6[Formula: see text]V.

Low phase noise GaAs HBT VCO in Ka-band

Design and fabrication of a Ka-band voltage-controlled oscillator (VCO) using commercially available 1-μm GaAs heterojunction bipolar transistor technology is presented. A fully differential common-emitter configuration with a symmetric capacitance with a symmetric inductance tank structure is employed to reduce the phase noise of the VCO, and a novel π-feedback network is applied to compensate for the 180° phase shift. The on-wafer test shows that the VCO exhibits a phase noise of −96.47 dBc/Hz at a 1 MHz offset and presents a tuning range from 28.312 to 28.695 GHz. The overall dc current consumption of the VCO is 18 mA with a supply voltage of −6 V The chip area of the VCO is 0.7 × 0.7 mm2.

Integration of Photodefinable Polybenzoxazole as Intermetal Dielectric for GaAs HBT Technology

Photodefinable polybenzoxazole (PBO) has been integrated as intermetal dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. Process module optimization and integration studies were performed and the results and process flow were compared to those of dry-etch polyimide. The photodefinable PBO is shown to allow the intermetal dielectric process flow to be simplified and the number of processes and equipment to be reduced. Results show that PBO has more planarity than polyimide, when coated on GaAs HBT wafers, which typically have significant topography. The photolithography coat, expose, and develop processes were optimized to obtain the desired dielectric thickness and the required via dimension and sidewall profile, in addition the removal of the PBO from the die street. The PBO thermal curing process was performed at 300oC, while plasma ashing was performed to remove any PBO residue from the bottom of the vias. These results show that the photodefinable PBO film is compatible with, is suitable for, and can be integrated as intermetal dielectric in GaAs HBT technology.

Integration of Photodefinable Polybenzoxazole as Intermetal Dielectric for GaAs HBT Technology

Polybenzoxazole (PBO) is a polymer dielectric that has excellent mechanical, physical, and electrical characteristics and that is used for various semiconductor thin film applications. The PBO has low dielectric constant, and has good thermal stability and thermo-oxidative resistance. Furthermore, the PBO material can be applied by spin-coating and can be cured at temperature of <300oC, which is significantly lower than many other spin-on dielectric materials. These characteristics make PBO suitable for use in many semiconductor technologies and applications that require the processing temperatures not to exceed 300oC, such as GaAs hetero-junction bipolar transistor (HBT) technology. The PBO material is easily processed, and can be made photodefinable by adding photoactive compounds, and therefore be patterned on semiconductor wafers. By using a photodefinable PBO dielectric material, there will not be any need to perform patterning by dry-etch process steps that are typically performed in GaAs technologies.In this study, photodefinable PBO has been integrated as intermetal dielectric in GaAs HBT technology. Process module optimization and integration studies were performed and the PBO results and process flow were compared to those of dry-etch polyimide, which is typically used as intermetal dielectric in GaAs technology. The photodefinable PBO is shown to allow the intermetal dielectric process flow to be simplified and the number of processes and equipments to be reduced. Results show that PBO has more planarity than polyimide, when coated on GaAs HBT wafers, which typically have significant topography. The PBO photolithography coat, expose, and develop processes were optimized in order to obtain the desired dielectric thickness and the required via dimension and sidewall profile, in addition to removing the PBO from the die street. The PBO thermal curing process was performed at 300oC, while ashing was performed to remove any PBO residue in the vias and streets. Figure 1 shows the FIB/SEM images of GaAs wafer after deposition of Metal 1 and coated with photodefinable, after via expose and develop, after cure, and after ash. Figure 2 shows the GaAs HBT wafer with (a) dry-etch polyimide and (b) photodefinable PBO used as intermetal dielectric. These results show that the photodefinable PBO film is compatible with, is suitable for, and can be integrated as intermetal dielectric in GaAs HBT technology.

A 6-bit 3-Gsps ADC implemented in 1 μm GaAs HBT technology

The design and test results of a 6-bit 3-Gsps analog-to-digital converter (ADC) using 1 μm GaAs heterojunction bipolar transistor (HBT) technology are presented. The monolithic folding-interpolating ADC makes use of a track-and-hold amplifier (THA) with a highly linear input buffer to maintain a highly effective number of bits (ENOB). The ADC occupies an area of 4.32 × 3.66 mm2 and achieves 5.53 ENOB with an effective resolution bandwidth of 1.1 GHz at a sampling rate of 3 Gsps. The maximum DNL and INL are 0.36 LSB and 0.48 LSB, respectively.

ALD HfO2 and Al2O3 as MIM Capacitor Dielectric for GaAs HBT Technology

Hafnium dioxide (HfO2) and aluminum oxide (Al2O3) films have been deposited using atomic layer deposition (ALD) method and have been evaluated and used as metal-insulator-metal (MIM) capacitor dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. The results show that the capacitor with 62 nm of ALD HfO2 resulted in a capacitance density of 2.73 fF/mm2, while that with 59 nm of ALD Al2O3 resulted in a capacitance density of 1.55 fF/mm2. This capacitance density increased, when the temperature was increased from 25 to 150oC. There was no significant change in capacitance density of these ALD films, when the applied voltage was varied from -5 to +5 V and when the frequency was increased from 1 kHz to 1 MHz. The breakdown voltage of the ALD hafnium dioxide and aluminum oxide films was measured to be at 34 V and 41 V, respectively. As the temperature was increased from 25 to 150oC, the breakdown voltage of both films decreased, while the leakage current increased. These results show that both ALD HfO2 and Al2O3 are compatible with, and suitable as MIM capacitor dielectric in GaAs HBT technology and can be adjusted to meet the specific application and requirements of the GaAs devices and designs.

Characterization of atomic layer deposition HfO2, Al2O3, and plasma-enhanced chemical vapor deposition Si3N4 as metal–insulator–metal capacitor dielectric for GaAs HBT technology

Characterization was performed on the application of atomic layer deposition (ALD) of hafnium dioxide (HfO2) and aluminum oxide (Al2O3), and plasma-enhanced chemical vapor deposition (PECVD) of silicon nitride (Si3N4) as metal–insulator–metal (MIM) capacitor dielectric for GaAs heterojunction bipolar transistor (HBT) technology. The results show that the MIM capacitor with 62 nm of ALD HfO2 resulted in the highest capacitance density (2.67 fF/μm2), followed by capacitor with 59 nm of ALD Al2O3 (1.55 fF/μm2) and 63 nm of PECVD Si3N4 (0.92 fF/μm2). The breakdown voltage of the PECVD Si3N4 was measured to be 73 V, as compared to 34 V for ALD HfO2 and 41 V for Al2O3. The capacitor with Si3N4 dielectric was observed to have lower leakage current than both with Al2O3 and HfO2. As the temperature was increased from 25 to 150 °C, the breakdown voltage decreased and the leakage current increased for all three films, while the capacitance increased for the Al2O3 and HfO2. Additionally, the capacitance of the ALD Al2O3 and HfO2 films was observed to change, when the applied voltage was varied from −5 to +5 V, while no significant change was observed on the capacitance of the PECVD Si3N4. Furhermore, no significant change in capacitance was seen for these silicon nitride, aluminum oxide, and hafnium dioxide films, as the frequency was increased from 1 kHz to 1 MHz. These results show that the ALD films of Al2O3 and HfO2 have good electrical characteristics and can be used to fabricate high density capacitor. As a result, these ALD Al2O3 and HfO2 films, in addition to PECVD Si3N4, are suitable as MIM capacitor dielectric for GaAs HBT technology, depending on the specific electrical characteristics requirements and application of the GaAs devices.

Fully Integrated 39 dBm, 3-Stage Doherty PA MMIC in a Low-Voltage GaAs HBT Technology

A power amplifier, designed and fabricated in a low voltage GaAs hetero-junction bipolar transistor technology with a Doherty output stage, is presented. A pre-driver, a driver, main and peaking amplifiers, bias circuits, a 90° power splitter, and the Doherty impedance transformer are integrated on a single chip. Measured key performance parameters include a P1dB compression point of at least 38.8 dBm over the US digital dividend band ranging from 728 to 768 MHz, and a PAE of 37% for a 5 MHz long term evolution downlink signal with 7.16 dB peak-to-average ratio.

12.5 Gbps 1:16 DEMUXIC with high speed synchronizing circuits

A 12.5 Gbps 1:16 demultiplexer (DEMUX) integrated circuit is presented for multi-channel high-speed data transmission. A novel high-speed synchronizing technique is proposed and integrated in this DEMUX chip. Compared with conventional synchronizing techniques, the proposed method largely simplifies the system configuration. The experimental result demonstrates that the proposed circuit is effective in two-channel synchronization under a clock frequency of 12.5 GHz. The circuit is realized using 1 μm GaAs heterojunction bipolar transistor technology with die area of 2.3 × 2.3 mm2.

Effects of Deposition Method of PECVD Silicon Nitride as MIM Capacitor Dielectric for GaAs HBT Technology

Thin silicon nitride (Si3N4) films deposited using plasma-enhanced chemical deposition (PECVD) method have been used as metal-insulator-metal (MIM) capacitor dielectric for GaAs hetero-junction bipolar transistor (HBT) technology. The characteristics of the films, which were deposited at 300oC, were found to be dependent on how the PECVD film was deposited. A silicon nitride film deposited as a multi-layer-layer film has different properties compared to a film deposited under the same processing conditions as a single layer film. When used as MIM capacitor dielectric, the multi-layer Si3N4 film is shown to have significantly superior and higher dielectric breakdown voltage and lower leakage current characteristics, as compared to the single layer film, while the capacitance density is found to be similar. Additionally, the multi-layer Si3N4 film is shown to have lower compressive stress and lower refractive index, indicating that the characteristics of the film are influenced by the additional interfaces present in a multi-layer film.

Photodefinable Polybenzoxazole as Interlevel Dielectric and Buffer Layer for GaAs HBT Technology

Polybenzoxazole (PBO) has been investigated and used as interlevel dielectric and buffer layer for GaAs hetero-junction bipolar transistor (HBT) technology. The polymer film is applied by spin-coating, and is photosensitive and photodefinable. These film characteristics allow the simplification of the process flow and allow the elimination of various steps that are typically used to define the vias, streets, and bonding pads. Additionally, this PBO film can be cured at low temperature (>250oC) and the resulting film has good characteristics against moisture absorption and is stable thermally. Furthermore, the film has good planarity and gapfill characteristics, and has excellent mechanical properties. Results show that GaAs device wafers fabricated with this film as interlevel dielectric has good electrical characteristics. When used as buffer layer, the PBO film is shown to be effective in mechanically protecting the underlying devices and interconnections. The use of photodefinable PBO will result in improvement in device quality and reliability, in addition to in significant reduction in capital and consumable cost, and reduction in cycle time of wafers manufactured. All the above characteristics make this PBO film to be well-suited as interlevel dielectric and buffer layer for and compatible with GaAs HBT technology.

Variable Frequency Microwave and Convection Furnace Curing of Polybenzoxazole Buffer Layer for GaAs HBT Technology

Photosensitive polybenzoxazole (PBO) film has been used in GaAs heterojunction bipolar transistor (HBT) technology for stress buffer and mechanical protection layer applications. However, this film needs to be cured at high temperatures for a long period of time in order to obtain its desired excellent material characteristics. High-temperature curing can result in degradation to the electrical characteristics and performance of the underlying GaAs devices due to limited thermal budget. In this paper, we have characterized the effects of curing the PBO film on GaAs HBT wafers using a conventional convection furnace and using a variable frequency microwave (VFM) furnace. The results show that a VFM cure can achieve similar excellent physical, mechanical, thermal, and chemical material characteristics at a lower curing temperature and in a much shorter time, as compared to convection furnace curing, therefore resulting in minimal GaAs device degradation. Based on these results, an optimum curing condition using the VFM method can be obtained that satisfies both stress buffer layer material and device requirements for GaAs HBT technology.

A New Design Approach for Low Phase-Noise Reflection-Type MMIC Oscillators

In this paper, optimization of the loaded quality factor Q/sub L/ for reflection-type heterojunction bipolar transistor (HBT) oscillators is investigated. The main result is an optimum relation between the S-parameter phases at the three transistor ports. A new design strategy for this type of oscillator is proposed. The analysis is verified by comparing several Ka-band monolithic-microwave integrated-circuit oscillators in GaAs HBT technology with different resonators. The measured loaded Q/sub L/ values correspond to the measured phase noise of the circuits. At an oscillation frequency of 33 GHz, an excellent phase noise of -87 dBc/Hz at 100-kHz offset frequency is achieved over the whole tuning range.