P. Chavarkar - Academia.edu (original) (raw)
Papers by P. Chavarkar
This material is posted here with permission of the IEEE. Such permission of the IEEE does not in... more This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Cree's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org By choosing to view this document, you agree to all provisions of the copyright laws protecting it. High Linearity, Robust, AlGaN-GaN HEMTs for LNA & Receiver ICs
2000 IEEE MTT-S International Microwave Symposium Digest (Cat. No.00CH37017)
Monolithic optically variable capacitors (OVC's) consisting of photovoltaic arrays integrated wit... more Monolithic optically variable capacitors (OVC's) consisting of photovoltaic arrays integrated with varactor diodes are used in bias free optical control of microwave circuits and antennas. The improved OVC's presented here required only 450 pW of optical power for a 2.2:l change in capacitance, a threefold reduction in optical power compared to previous results. Using these improved OVC's, bias free optical control of phase shifters and slot antennas has been demonstrated with the lowest reported optical power.
Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97, 1997
Optical fiber links are low loss, light weight, compact, immune against EM1 and do not interfere ... more Optical fiber links are low loss, light weight, compact, immune against EM1 and do not interfere with the radiation patterns of antennas. This makes them attractive for the control of microwave circuits and antennna arrays. In this paper we report a monolithic implementation of an Optically Variable Capacitor. This consists of a photovoltaic array that generates a light dependent reverse bias voltage across a varactor diode. The fabrication of miniature photovoltaic arrays poses some interesting challenges which are addressed in this paper. The DC characteristics of the photovoltaic arrays and RF measurements on the entire Optically Variable Capacitor are presented.
Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97, 1997
The growing field of wireless communication has necessitated the need for ultra low power, high s... more The growing field of wireless communication has necessitated the need for ultra low power, high speed transistor technology. Low gate leakage in FETs is required for several applications, most notably low power high-speed ICs and high reliability power amplifiers. Furthermore, enhancement-mode FETs with low gate-leakage necessary for dense low power ICs are currently extremely difficult to achieve. An insulator gate
Electrical Engineering Handbook, 2007
IEEE Electron Device Letters, 2003
eScholarship provides open access, scholarly publishing services to the University of California ... more eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide.
Applied Optics, 1999
A technique is proposed for the extraction of precise values of field-dependent absorption coeffi... more A technique is proposed for the extraction of precise values of field-dependent absorption coefficient ␣ and refractive index n from photocurrent and transmittance measurements of optical modulator structures. The technique uses approximate results of ␣ and n extracted from a simplified device as the initial input into an iterative procedure that utilizes the consistency between ␣ and n to obtain successively better estimates of these parameters. The technique was applied to results that were measured experimentally, and we verified the accuracy by using synthetic data. Errors caused by measurement inaccuracy are also investigated. It is shown that the absorption coefficient has a modest sensitivity whereas the refractive index is insensitive to these errors.
Optical Fiber …, 2007
The first generation InP based Large Scale Photonic Integrated Circuits (LS-PIC) have been succes... more The first generation InP based Large Scale Photonic Integrated Circuits (LS-PIC) have been successfully deployed in the field for over two years now [1]. LS-PIC's have been shown to be highly manufacturable [2, 3], and reliable to meet the stringent requirements of carrier ...
Journal of Optical Networking, 2007
͑Doc. ID 74860͒ Dense wavelength division multiplexed (DWDM) large-scale, single-chip transmitter... more ͑Doc. ID 74860͒ Dense wavelength division multiplexed (DWDM) large-scale, single-chip transmitter and receiver photonic integrated circuits (PICs), each capable of operating at 100 Gbits/ s, have been deployed in the field since the end of 2004. These highly integrated InP chips have significantly changed the economics of long-haul optical transport networks. First, a review of the tenchannel, 100 Gbits/ s PIC is presented. Then two extensions of the technology are demonstrated; first is wide temperature, coolerless operation of the 100 Gbits/ s PIC, and second is a single integrated chip with 40 channels operating at 40 Gbits/ s, capable of an aggregate data rate of 1.6 Tbits/ s.
Gallium Nitride (GaN) based HEMTs have the potential for being the highest performance power comp... more Gallium Nitride (GaN) based HEMTs have the potential for being the highest performance power compound semiconductor microwave transistors. In this paper, we review the performance and present results on device scaling for the AlGaN-GaN HEMTs. In particular, 1 and 2 mm wide HEMTs resulted in 8.5 W and 14.5 W output power respectively at X-band with close to 40 % power added efficiency.
IEDM Technical Digest. IEEE International Electron Devices Meeting, 2004.
GaN HEMTs with field-plates connected to the source terminal have been developed for high-gain, h... more GaN HEMTs with field-plates connected to the source terminal have been developed for high-gain, high-voltage operation at microwave frequencies. Due to the reduced feedback capacitance compared to the gate-terminated field-plate structures, improvement in large-signal gain of 5-7 dB is obtained. Superior performance including 21-dB associated gain, 20-W/mm output power and 60% power-added-efficiency at 4 GHz and 118V bias, is achieved simultaneously. This translates to an extremely high voltage-frequency-gain product approaching 10 kV-GHz.
Thin Films, 2001
Abstract This chapter discusses the principles of operation and applications of field effect tran... more Abstract This chapter discusses the principles of operation and applications of field effect transistors. Field effect transistors, specifically high electron mobility transistors (HEMTs) or modulation-doped field-effect transistors are being extensively used in low noise and power amplifiers at microwave and millimeter-wave frequencies. The chapter begins with a discussion of current voltage and charge control mechanisms in HEMTs and this is followed by discussion of small-signal and large-signal equivalent circuit models of FET (which are used in circuit design). As operation at high frequencies is enabled by reduction in gate length, issues relating to device scaling are discussed. Issues related to operation of FETs as low-noise and power amplifier devices are discussed. The emergence of crystal growth techniques including molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has enabled the fabrication of HEMTs using a variety of material systems. The selection of a material system depends on application and operating frequency. The AlGaAs/InGaAs pseudomorphic HEMT and the AlInAs/GaInAs HEMT are the two most widely used device structures. The performance of these devices as low-noise and power amplification devices is summarized. These devices have recently demonstrated their ability for insertion in high-volume commercial applications such as wireless and optical communication systems. This chapter therefore discusses the various design issues involving power amplifiers for wireless handsets and the suitability of GaAs p HEMTs for this application. The AlInAs/GaInAs HEMT with its high current density and superior high frequency performance has enabled the fabrication of digital circuits operating at 80 Gb/s. The various issues related to application of AlInAs/GaInAs HEMT for digital circuits are also discussed.
Solid-State Electronics, 1996
We have developed a simple technology for monolithic integration of resonant tunneling diodes (RT... more We have developed a simple technology for monolithic integration of resonant tunneling diodes (RTDs) and heterostructure junction-modulated field effect transistors (HJFETs). We have achieved good device performance with this technology: HJFETs had transconductances of 290 mS/mm and current densities of 310 mA/mm for a 1.5/zm gate length; RTDs had room temperature peak to valley ratios greater than 20:1 with current densities of 42 kA/cm 2. With this technology, we have demonstrated a monolithically integrated RTD + HJFET state holding circuit that can serve as a building block circuit for self-timed logic units. This circuit is resistor-free and operates at room temperature. The state holding circuit showed large noise margins of 1.21 V and 0.71 V, respectively, for input low and input high, for a 1.7 V input voltage swing. We have examined the transient response of the circuit and investigated the effect of circuit design parameters on propagation delay. We identify the RTD valley current as the limiting factor on propagation delay. We discuss the suitability of RTD + HJFET circuits such as our state holding circuit for highly dense integrated circuits.
IEEE Electron Device Letters, 1996
The super self-aligned submicron single-metal FET (SASSFET), a FET-based integrated circuit techn... more The super self-aligned submicron single-metal FET (SASSFET), a FET-based integrated circuit technology suitable for fabrication of high-speed GaAs and InP circuits, is demonstrated. With nonalloyed source and drain contacts done by MOCVD regrowth, the SASSFET is a uniform, dense, selfaligned, single-metal technology that achieves submicron dimensions with optical lithography. A 0.4 pm gate length junction HFET fabricated with the SASSFET technology has a transconductance of 380 mS/mm and a good high-frequency performance with f7 of 45 GHz and fmax of 80 GHz.
MRS Proceedings, 1998
We demonstrate a new approach to the growth of dislocation free lattice-mismatched materials on G... more We demonstrate a new approach to the growth of dislocation free lattice-mismatched materials on GaAs substrates using Al2O3 interlayers obtained by lateral oxidation of AlAs. This is achieved by generating relaxed low threading dislocation density InGaAs templates which are mechanically supported but epitaxially decoupled from the host GaAs substrate. This process uses the phenomena of relaxation of strained coherent hypercritical thickness (h > hcritical,) layer in direct contact with an oxidizing Al-containing semiconductor (i.e. AlAs or AlGaAs). 5000 Å In0.11Ga0.89As layers were then grown on the In0.2 Ga0.8As/Al2O3/GaAs template which acts as a pseudo-substrate (lattice-engineered substrate). The epitaxial layers are partially relaxed and have extremely smooth surface morphology. Further TEM micrographs of these epitaxial layers show no misfit dislocations or related localized strain fields at the In0.2Ga0.8As/Al2O3 interface. The absence of misfit dislocations or local strai...
Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97, 1997
Conference Proceedings. 1997 International Conference on Indium Phosphide and Related Materials, 1997
We propose a novel lateral bandgap engineering technique to improve electron transport in the cha... more We propose a novel lateral bandgap engineering technique to improve electron transport in the channel of an AlInAs/GaInAs HEMT. Electrons are launched at the source with higher velocity by a launcher (higher bandgap AlInAs source) and collected at the drain by a heterojunction collector (lower bandgap InAs drain). The resulting device, a Lateral Bandgap Engineered HEMT (LBE-HEMT), is analyzed using
1995 53rd Annual Device Research Conference Digest, 1995
Proceedings. IEEE Lester Eastman Conference on High Performance Devices, 2002
Directorate, WPAFB, OH 45433. 0-7803-7478/02/$17.00 0 2002 IEEE
International Electron Devices Meeting. Technical Digest, 1996
ABSTRACT
This material is posted here with permission of the IEEE. Such permission of the IEEE does not in... more This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Cree's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org By choosing to view this document, you agree to all provisions of the copyright laws protecting it. High Linearity, Robust, AlGaN-GaN HEMTs for LNA & Receiver ICs
2000 IEEE MTT-S International Microwave Symposium Digest (Cat. No.00CH37017)
Monolithic optically variable capacitors (OVC's) consisting of photovoltaic arrays integrated wit... more Monolithic optically variable capacitors (OVC's) consisting of photovoltaic arrays integrated with varactor diodes are used in bias free optical control of microwave circuits and antennas. The improved OVC's presented here required only 450 pW of optical power for a 2.2:l change in capacitance, a threefold reduction in optical power compared to previous results. Using these improved OVC's, bias free optical control of phase shifters and slot antennas has been demonstrated with the lowest reported optical power.
Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97, 1997
Optical fiber links are low loss, light weight, compact, immune against EM1 and do not interfere ... more Optical fiber links are low loss, light weight, compact, immune against EM1 and do not interfere with the radiation patterns of antennas. This makes them attractive for the control of microwave circuits and antennna arrays. In this paper we report a monolithic implementation of an Optically Variable Capacitor. This consists of a photovoltaic array that generates a light dependent reverse bias voltage across a varactor diode. The fabrication of miniature photovoltaic arrays poses some interesting challenges which are addressed in this paper. The DC characteristics of the photovoltaic arrays and RF measurements on the entire Optically Variable Capacitor are presented.
Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97, 1997
The growing field of wireless communication has necessitated the need for ultra low power, high s... more The growing field of wireless communication has necessitated the need for ultra low power, high speed transistor technology. Low gate leakage in FETs is required for several applications, most notably low power high-speed ICs and high reliability power amplifiers. Furthermore, enhancement-mode FETs with low gate-leakage necessary for dense low power ICs are currently extremely difficult to achieve. An insulator gate
Electrical Engineering Handbook, 2007
IEEE Electron Device Letters, 2003
eScholarship provides open access, scholarly publishing services to the University of California ... more eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide.
Applied Optics, 1999
A technique is proposed for the extraction of precise values of field-dependent absorption coeffi... more A technique is proposed for the extraction of precise values of field-dependent absorption coefficient ␣ and refractive index n from photocurrent and transmittance measurements of optical modulator structures. The technique uses approximate results of ␣ and n extracted from a simplified device as the initial input into an iterative procedure that utilizes the consistency between ␣ and n to obtain successively better estimates of these parameters. The technique was applied to results that were measured experimentally, and we verified the accuracy by using synthetic data. Errors caused by measurement inaccuracy are also investigated. It is shown that the absorption coefficient has a modest sensitivity whereas the refractive index is insensitive to these errors.
Optical Fiber …, 2007
The first generation InP based Large Scale Photonic Integrated Circuits (LS-PIC) have been succes... more The first generation InP based Large Scale Photonic Integrated Circuits (LS-PIC) have been successfully deployed in the field for over two years now [1]. LS-PIC's have been shown to be highly manufacturable [2, 3], and reliable to meet the stringent requirements of carrier ...
Journal of Optical Networking, 2007
͑Doc. ID 74860͒ Dense wavelength division multiplexed (DWDM) large-scale, single-chip transmitter... more ͑Doc. ID 74860͒ Dense wavelength division multiplexed (DWDM) large-scale, single-chip transmitter and receiver photonic integrated circuits (PICs), each capable of operating at 100 Gbits/ s, have been deployed in the field since the end of 2004. These highly integrated InP chips have significantly changed the economics of long-haul optical transport networks. First, a review of the tenchannel, 100 Gbits/ s PIC is presented. Then two extensions of the technology are demonstrated; first is wide temperature, coolerless operation of the 100 Gbits/ s PIC, and second is a single integrated chip with 40 channels operating at 40 Gbits/ s, capable of an aggregate data rate of 1.6 Tbits/ s.
Gallium Nitride (GaN) based HEMTs have the potential for being the highest performance power comp... more Gallium Nitride (GaN) based HEMTs have the potential for being the highest performance power compound semiconductor microwave transistors. In this paper, we review the performance and present results on device scaling for the AlGaN-GaN HEMTs. In particular, 1 and 2 mm wide HEMTs resulted in 8.5 W and 14.5 W output power respectively at X-band with close to 40 % power added efficiency.
IEDM Technical Digest. IEEE International Electron Devices Meeting, 2004.
GaN HEMTs with field-plates connected to the source terminal have been developed for high-gain, h... more GaN HEMTs with field-plates connected to the source terminal have been developed for high-gain, high-voltage operation at microwave frequencies. Due to the reduced feedback capacitance compared to the gate-terminated field-plate structures, improvement in large-signal gain of 5-7 dB is obtained. Superior performance including 21-dB associated gain, 20-W/mm output power and 60% power-added-efficiency at 4 GHz and 118V bias, is achieved simultaneously. This translates to an extremely high voltage-frequency-gain product approaching 10 kV-GHz.
Thin Films, 2001
Abstract This chapter discusses the principles of operation and applications of field effect tran... more Abstract This chapter discusses the principles of operation and applications of field effect transistors. Field effect transistors, specifically high electron mobility transistors (HEMTs) or modulation-doped field-effect transistors are being extensively used in low noise and power amplifiers at microwave and millimeter-wave frequencies. The chapter begins with a discussion of current voltage and charge control mechanisms in HEMTs and this is followed by discussion of small-signal and large-signal equivalent circuit models of FET (which are used in circuit design). As operation at high frequencies is enabled by reduction in gate length, issues relating to device scaling are discussed. Issues related to operation of FETs as low-noise and power amplifier devices are discussed. The emergence of crystal growth techniques including molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has enabled the fabrication of HEMTs using a variety of material systems. The selection of a material system depends on application and operating frequency. The AlGaAs/InGaAs pseudomorphic HEMT and the AlInAs/GaInAs HEMT are the two most widely used device structures. The performance of these devices as low-noise and power amplification devices is summarized. These devices have recently demonstrated their ability for insertion in high-volume commercial applications such as wireless and optical communication systems. This chapter therefore discusses the various design issues involving power amplifiers for wireless handsets and the suitability of GaAs p HEMTs for this application. The AlInAs/GaInAs HEMT with its high current density and superior high frequency performance has enabled the fabrication of digital circuits operating at 80 Gb/s. The various issues related to application of AlInAs/GaInAs HEMT for digital circuits are also discussed.
Solid-State Electronics, 1996
We have developed a simple technology for monolithic integration of resonant tunneling diodes (RT... more We have developed a simple technology for monolithic integration of resonant tunneling diodes (RTDs) and heterostructure junction-modulated field effect transistors (HJFETs). We have achieved good device performance with this technology: HJFETs had transconductances of 290 mS/mm and current densities of 310 mA/mm for a 1.5/zm gate length; RTDs had room temperature peak to valley ratios greater than 20:1 with current densities of 42 kA/cm 2. With this technology, we have demonstrated a monolithically integrated RTD + HJFET state holding circuit that can serve as a building block circuit for self-timed logic units. This circuit is resistor-free and operates at room temperature. The state holding circuit showed large noise margins of 1.21 V and 0.71 V, respectively, for input low and input high, for a 1.7 V input voltage swing. We have examined the transient response of the circuit and investigated the effect of circuit design parameters on propagation delay. We identify the RTD valley current as the limiting factor on propagation delay. We discuss the suitability of RTD + HJFET circuits such as our state holding circuit for highly dense integrated circuits.
IEEE Electron Device Letters, 1996
The super self-aligned submicron single-metal FET (SASSFET), a FET-based integrated circuit techn... more The super self-aligned submicron single-metal FET (SASSFET), a FET-based integrated circuit technology suitable for fabrication of high-speed GaAs and InP circuits, is demonstrated. With nonalloyed source and drain contacts done by MOCVD regrowth, the SASSFET is a uniform, dense, selfaligned, single-metal technology that achieves submicron dimensions with optical lithography. A 0.4 pm gate length junction HFET fabricated with the SASSFET technology has a transconductance of 380 mS/mm and a good high-frequency performance with f7 of 45 GHz and fmax of 80 GHz.
MRS Proceedings, 1998
We demonstrate a new approach to the growth of dislocation free lattice-mismatched materials on G... more We demonstrate a new approach to the growth of dislocation free lattice-mismatched materials on GaAs substrates using Al2O3 interlayers obtained by lateral oxidation of AlAs. This is achieved by generating relaxed low threading dislocation density InGaAs templates which are mechanically supported but epitaxially decoupled from the host GaAs substrate. This process uses the phenomena of relaxation of strained coherent hypercritical thickness (h > hcritical,) layer in direct contact with an oxidizing Al-containing semiconductor (i.e. AlAs or AlGaAs). 5000 Å In0.11Ga0.89As layers were then grown on the In0.2 Ga0.8As/Al2O3/GaAs template which acts as a pseudo-substrate (lattice-engineered substrate). The epitaxial layers are partially relaxed and have extremely smooth surface morphology. Further TEM micrographs of these epitaxial layers show no misfit dislocations or related localized strain fields at the In0.2Ga0.8As/Al2O3 interface. The absence of misfit dislocations or local strai...
Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97, 1997
Conference Proceedings. 1997 International Conference on Indium Phosphide and Related Materials, 1997
We propose a novel lateral bandgap engineering technique to improve electron transport in the cha... more We propose a novel lateral bandgap engineering technique to improve electron transport in the channel of an AlInAs/GaInAs HEMT. Electrons are launched at the source with higher velocity by a launcher (higher bandgap AlInAs source) and collected at the drain by a heterojunction collector (lower bandgap InAs drain). The resulting device, a Lateral Bandgap Engineered HEMT (LBE-HEMT), is analyzed using
1995 53rd Annual Device Research Conference Digest, 1995
Proceedings. IEEE Lester Eastman Conference on High Performance Devices, 2002
Directorate, WPAFB, OH 45433. 0-7803-7478/02/$17.00 0 2002 IEEE
International Electron Devices Meeting. Technical Digest, 1996
ABSTRACT