Wideband Watt-Level Spatial Power-Combined Power Amplifier in SiGe BiCMOS Technology for Efficient mm-Wave Array Transmitters

The continued demand for high-speed wireless communications is driving the development of integrated high-power transmitters at millimeter wave (mm-Wave) frequencies. Si-based technologies allow achieving a high level of integration but usually provide insufficient generated RF power to compensate for the increased propagation and material losses at mm-Wave bands due to the relatively low breakdown voltage of their devices. This problem can be reduced significantly if one could combine the power of multiple active devices on each antenna element. However, conventional on-chip power combining networks have inherently high insertion losses reducing transmitter efficiency and limiting its maximum achievable output power.This work presents a non-conventional design approach for mm-Wave Si-based Watt-level power amplifiers that is based on novel power-combining architecture, where an array of parallel custom PA-cells suited on the same chip is interfaced to a single substrate integrated waveguide (to be a part of an antenna element). This allows one to directly excite TEm0 waveguide modes with high power through spatial power combining functionality, obviating the need for intermediate and potentially lossy on-chip power combiners. The proposed solution offers wide impedance bandwidth (50%) and low insertion losses (0.4 dB), which are virtually independent from the number of interfaced PA-cells. The work evaluates the scalability bounds of the architecture as well as discusses the critical effects of coupled non-identical PA-cells, which are efficiently reduced by employing on-chip isolation load resistors.The proposed architecture has been demonstrated through an example of the combined PA with four differential cascode PA-cells suited on the same chip, which is flip-chip interconnected to the combiner placed on a laminate. This design is implemented in a 0.25 um SiGe BiCMOS technology. The PA-cell has a wideband performance (38.6%) with both high peak efficiency (30%) and high saturated output power (24.9 dBm), which is the highest reported output power level obtained without the use of circuit-level power combining in Si-based technologies at Ka-band. In order to achieve the optimal system-level performance of the combined PA, an EM-circuit-thermal optimization flow has been proposed, which accounts for various multiphysics effects occurring in the joint structure. The final PA achieves the peak PAE of 26.7% in combination with 30.8 dBm maximum saturated output power, which is the highest achievable output power in practical applications, where the 50-Ohms load is placed on a laminate. The high efficiency (>20%) and output power (>29.8 dBm) over a wide frequency range (30%) exceed the state-of-the-art in Si-based PAs

Implantable Low-Noise Fiberless Optoelectrodes for Optogenetic Control of Distinct Neural Populations

The mammalian brain is often compared to an electrical circuit, and its dynamics and function are governed by communication across different types neurons. To treat neurological disorders like Alzheimer’s and Parkinson’s, which are characterized by inhibition or amplification of neural activity in a particular region or lack of communication between different regions of the brain, there is a need to understand troubleshoot neural networks at cellular or local circuit level. In this work, we introduce a novel implantable optoelectrode that can manipulate more than one neuron type at a single site, independently and simultaneously. By delivering multi-color light using a scalable optical waveguide mixer, we demonstrate manipulation of multiple neuron types at precise spatial locations in vivo for the first time. We report design, micro-fabrication and optoelectronic packaging of a fiber-less, multicolor optoelectrode. The compact optoelectrode design consists of a 7 μm x 30 μm dielectric optical waveguide mixer and eight electrical recording sites monolithically integrated on each shank of a 22 μm-thick four-shank silicon neural probe. The waveguide mixers are coupled to eight side-emitting injection laser diodes (ILDs) via gradient-index (GRIN) lenses assembled on the probe backend. GRIN-based optoelectrode enables efficient optical coupling with large alignment tolerance to provide wide optical power range (10 to 3000 mW/mm2 irradiance) at stimulation ports. It also keeps thermal dissipation and electromagnetic interference generated by light sources sufficiently far from the sensitive neural signals, allowing thermal and electrical noise management on a multilayer printed circuit board. We demonstrated device verification and validation in CA1 pyramidal layer of mice hippocampus in both anesthetized and awake animals. The packaged devices were used to manipulate variety of multi-opsin preparations in vivo expressing different combinations of Channelrhodopsin-2, Archaerhodopsin and ChrimsonR in pyramidal and parvalbumin interneuron cells. We show effective stimulation, inhibition and recording of neural spikes at precise spatial locations with less than 100 μV stimulation-locked transients on the recording channels, demonstrating novel use of this technology in the functional dissection of neural circuits.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137171/1/kkomal_1.pd

The 2023 terahertz science and technology roadmap

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz-∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation

The 2023 terahertz science and technology roadmap

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a 'snapshot' introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation

Development and Characterization of Auto-Locked Laser Systems and Applications to Photon Echo Lifetime Measurements

We have developed and characterized a new class of vacuum-sealed, auto-locking diode laser systems with an auto-locking controller that allows these instruments to be operated with greater ease and control at desired wavelengths in the visible and near-infrared spectral range. These laser systems can be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We show that these lasers have exceptional long-term stability, with an Allan deviation (ADEV) floor of 210^{-12}, and a short-term linewidth of 200 kHz. These performance characteristics are related to reducing current noise and ensuring vacuum sealing. We demonstrate accurate measurements of gravitational acceleration at the level of a few parts-per-billion by incorporating the laser into an industrial gravimeter. We also realize the basis of a LIDAR transmitter that can potentially operate in a spectral range in which frequency references are not readily available. We have also developed a technique for precise measurements of atomic lifetimes using optical photon echoes. We report a measurement of 26.10(3) ns for the 5^2P_{3/2} excited-state in ^{85}Rb vapour that has a statistical uncertainty of 0.11% in 4 hours of data acquisition. We show that the best statistical uncertainty that can be obtained with the current configuration is 0.013%, which has been exceeded by only one other lifetime measurement. An analysis of the technical limitations based on a simple model shows that these limitations can be overcome using a feedback loop with a reference interferometer. Our studies indicate that it should be possible to investigate systematic effects at the level of 0.03% in 10 minutes of data acquisition. Such an outcome could potentially result in the most accurate measurement of any atomic lifetime

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Design of a high-power 48GHz gyroklystron amplifier for accelerator applications

As the technology of radiofrequency linear accelerators (RF linacs) continues to improve, higher frequency acceleration systems become of interest as the achievable acceleration gradient has a dependence on frequency. Using a high driving frequency requires the consideration of many technological challenges. One such challenge is mitigating the effect of nonlinearities introduced during the electron acceleration and bunching process. To counteract the nonlinearity, an additional cavity at a harmonic of the main driving frequency can be included. This technique is known as harmonic linearisation. In existing C-band systems, harmonic linearisation can be achieved with an X-band structure, but if the main frequency is X-band, the lineariser must be Ka-band or higher. Linear klystrons are a well-developed technology and can reliably deliver tens of MW at X-band, but they are subject to a steep drop-off in achievable output power toward the Ka-band. The different interaction mechanism in a gyroklystron, based on phase-modulation of a helical beam, allows it to deliver multi-MW output power at significantly higher frequencies. The gyroklystron is therefore a strong candidate for delivering power to high-frequency linearising cavities. The international collaboration, CompactLight, is developing a design for a sophisticated X-ray Free Electron Laser (XFEL) with wide ranging research applications [1, 2]. The project required the consideration of both a 36GHz and 48GHz lineariser options. In each case, the development of new amplifiers was required to deliver sufficient power for the application. This thesis presents the design and analysis of a gyroklystron appropriate to drive a 48GHz linearising cavity. While the research presented in this thesis was performed with direct consideration of the CompactLight XFEL, its relevance is not exclusive to this project. With the performance of the microwave amplifier presented in this thesis, a lineariser at 48GHz could be a viable option for other C-band or X-band accelerator applications. Gyroklystron research was historically focused on radar applications. Since 48GHz lies in a frequency band unfavourable for atmospheric transmission, the development of components in this band has been lacking. The design presented in this thesis is the first published work on a MW-level amplifier at 48GHz and marks a step toward this frequency becoming a desirable choice for linearisation systems in future linacs. A gyroklystron design, including the electron source, vacuum windows, and input coupler has been designed through detailed simulation work. A triode-type magnetron injection gun compatible with a 2.02T axial guide magnetic field was designed and simulated. Applying -140kV to the cathode and -107.5kV to the modulating anode resulted in a gyrating electron beam with a current of 37A, guiding centre radius of 1.77mm, and velocity ratio spread of 8.9%. This resulted in a predicted gyroklystron output power of 2.0MW with a gain of 35dB at an efficiency of 38.6%.As the technology of radiofrequency linear accelerators (RF linacs) continues to improve, higher frequency acceleration systems become of interest as the achievable acceleration gradient has a dependence on frequency. Using a high driving frequency requires the consideration of many technological challenges. One such challenge is mitigating the effect of nonlinearities introduced during the electron acceleration and bunching process. To counteract the nonlinearity, an additional cavity at a harmonic of the main driving frequency can be included. This technique is known as harmonic linearisation. In existing C-band systems, harmonic linearisation can be achieved with an X-band structure, but if the main frequency is X-band, the lineariser must be Ka-band or higher. Linear klystrons are a well-developed technology and can reliably deliver tens of MW at X-band, but they are subject to a steep drop-off in achievable output power toward the Ka-band. The different interaction mechanism in a gyroklystron, based on phase-modulation of a helical beam, allows it to deliver multi-MW output power at significantly higher frequencies. The gyroklystron is therefore a strong candidate for delivering power to high-frequency linearising cavities. The international collaboration, CompactLight, is developing a design for a sophisticated X-ray Free Electron Laser (XFEL) with wide ranging research applications [1, 2]. The project required the consideration of both a 36GHz and 48GHz lineariser options. In each case, the development of new amplifiers was required to deliver sufficient power for the application. This thesis presents the design and analysis of a gyroklystron appropriate to drive a 48GHz linearising cavity. While the research presented in this thesis was performed with direct consideration of the CompactLight XFEL, its relevance is not exclusive to this project. With the performance of the microwave amplifier presented in this thesis, a lineariser at 48GHz could be a viable option for other C-band or X-band accelerator applications. Gyroklystron research was historically focused on radar applications. Since 48GHz lies in a frequency band unfavourable for atmospheric transmission, the development of components in this band has been lacking. The design presented in this thesis is the first published work on a MW-level amplifier at 48GHz and marks a step toward this frequency becoming a desirable choice for linearisation systems in future linacs. A gyroklystron design, including the electron source, vacuum windows, and input coupler has been designed through detailed simulation work. A triode-type magnetron injection gun compatible with a 2.02T axial guide magnetic field was designed and simulated. Applying -140kV to the cathode and -107.5kV to the modulating anode resulted in a gyrating electron beam with a current of 37A, guiding centre radius of 1.77mm, and velocity ratio spread of 8.9%. This resulted in a predicted gyroklystron output power of 2.0MW with a gain of 35dB at an efficiency of 38.6%

Cost benefit analysis of space communications technology. Volume 2: Final report

For abstract, see preceding accession