A broadband noise measurement system is newly developed and demonstrated at temperatures between ... more A broadband noise measurement system is newly developed and demonstrated at temperatures between 3 K and 300 K. Using the system, wideband noise spectroscopy (WBNS) from 20 kHz to 500 MHz is carried out for the first time, revealing that shot noise is the dominant white noise down to 3 K. The paper also suggests, by means of WBNS, the possibility of extracting the baseline noise characteristics, which do not include the noise component that varies a great deal from device to device.
We propose a methodology of variable-temperature broadband noise characterization for cryogenic M... more We propose a methodology of variable-temperature broadband noise characterization for cryogenic MOSFETs. A DUT is mounted on a reusable PCB vehicle with a built-in low-noise amplifier, and loaded into a cryogenic chamber. Using the vehicle, we measured flicker (low frequency) and white noise, and have successfully revealed dominance of shot noise in the temperature range from 300 to 120 K for the first time.
IEEE Transactions on Microwave Theory and Techniques, 2023
A signal flow graph (SFG) representation of smallsignal responses of nonlinear microwave circuits... more A signal flow graph (SFG) representation of smallsignal responses of nonlinear microwave circuits around a largesignal operating point is developed using the X-parameters. It is shown that, unlike the SFGs for linear circuits, negativefrequency nodes need to be included explicitly. The development elucidates the circuit-operational meaning of the elusive T-type small-signal X-parameters, which represent the interaction between positive-and negative-frequency components. As an example, such an SFG is used to derive a closed-form expression of the output power of an amplifier as a function of the load reflection coefficient. It is then used to plot approximate loadpull power contours. The result is consistent with the expressions of the optimum load reflection coefficient derived by Root et al. (EuMIC 2017) and power contours derived by Peláez-Pérez et al. (TMTT 2013). SFGs provide an alternative systematic means to derive closed-form expressions in terms of X-parameters and gain illuminating insights into the workings of weakly nonlinear circuits.
A broadband noise measurement system is newly developed and demonstrated at temperatures between ... more A broadband noise measurement system is newly developed and demonstrated at temperatures between 3 K and 300 K. Using the system, wideband noise spectroscopy (WBNS) from 20 kHz to 500 MHz is carried out for the first time, revealing that shot noise is the dominant white noise down to 3 K. The paper also suggests, by means of WBNS, the possibility of extracting the baseline noise characteristics, which do not include the noise component that varies a great deal from device to device.
It is known that designing an LNA for its minimum noise figure (NF) is not the best if the design... more It is known that designing an LNA for its minimum noise figure (NF) is not the best if the design goal is the lowest NF of the entire receiver (RX). A better LNA performance metric is the noise measure (NM). However, if feedback is allowed, the minimum NM can be realized with different combinations of NF and available gain, depending on which the RX NF changes. This paper theoretically studies the low-noise performance limit of an RX when lossless feedback is applied to its LNA. Somewhat counterintuitively, the lowest possible RX NF is shown to be realized when the LNA NM is slightly off its minimum NM. A new noise performance metric, $\Xi$, is introduced. The RX NF is shown to be minimized when $\Xi$ of LNA is minimized. Unlike NM, $\Xi$ is applicable even when the first stage of an RX is passive, as in a passive-mixer-first THz RX.
A physics-based equivalent circuit model of the ceramic capacitor is proposed, which can reproduc... more A physics-based equivalent circuit model of the ceramic capacitor is proposed, which can reproduce frequency characteristics of its impedance including the often observed yet hitherto physically unexplained kinks appearing above the primary series resonance frequency. The model can also account for parasitic effects of external inductances. In order to efficiently analyze and gain engineering insight into ceramic capacitors with a large number of metallic laminae, a two-dimensional method of moments is developed that treats the laminar structure as a uniform, effective medium. It turns out that the primary resonance and the kinks can be well understood and modeled by a lossy transmission line stub with a drastic wavelength reduction. The capacitor model is completed by adding components describing the skin effect and external inductances. The modeled impedance stays within a 4% margin of error up to 5 GHz. The proposed model could greatly improve the accuracy of power distribution network simulation.
Journal of Physics: Condensed Matter, Jul 25, 2000
The effect of a tunnelling electron on the tunnel barrier shape is studied at the limit where a s... more The effect of a tunnelling electron on the tunnel barrier shape is studied at the limit where a static image charge model is applicable. It is shown that the single-electron tunnelling current through an ultrasmall voltage-biased junction is not proportional to the junction area because of charging at the electrodes. Simple expressions are presented for the effective static barrier shape of a voltage-biased junction and of a junction in a circuit, the former of which accounts for the anomalous current scaling. A possible experimental arrangement for verifying the scaling relationship is suggested, with numerical results.
Coulomb blockade devices can circumvent some of the problems that arise from the continuing minia... more Coulomb blockade devices can circumvent some of the problems that arise from the continuing miniaturization of conventional circuits. However, device miniaturization and higher circuit integration aggravate cross-coupling phenomena in Coulomb blockade circuits. As an example, a silicon-based bidirectional electron pump was electrically characterized with emphasis on cross-coupling arising from the clock signal driving the pump. The cross-coupling alters profoundly the expected device characteristics, and the experimental data are confirmed by Monte Carlo simulations.
This paper presents an experimentally found device-size-independent universal relationship betwee... more This paper presents an experimentally found device-size-independent universal relationship between the settling time of floating-body silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) and the substrate current in body-tied devices. Such a relationship could enable one to characterize dynamic properties of SOI MOSFETs through DC measurements and would be useful for physical compact modeling of history effects.
A method of failure analysis is developed based on probability theory. Unlike Monte Carlo methods... more A method of failure analysis is developed based on probability theory. Unlike Monte Carlo methods, it produces accurate results even when the probabilities of interest differ from one another by many orders of magnitude. The method is applied to the analysis of the leakagecurrent distribution of double-gate MOSFETs and the microscopic failure mechanism is identified that limits the final yield. It explains experimental data very well. The insight into the failure mechanism gives clear guidelines for yield enhancement and facilitates device design together with the quantitative yield prediction.
This paper reports a CMOS power amplifier (PA) designed considering the performance degradation o... more This paper reports a CMOS power amplifier (PA) designed considering the performance degradation of MOSFETs caused by both temperature variations and the hot-carrier effect. A small-signal MOSFET model that reproduces the transient degradation caused by the hot-carrier effect is proposed. A 79 GHz CMOS PA was designed utilizing the proposed small-signal model. Simulation results agreed well with the measurement results of the PA fabricated with a 40 nm CMOS technology. It achieved the small-signal gain variations of below 0.7 dB and the OP1dB degradation of less than 0.8 dB in the temperature range of 0°C to 100°C.
The gain and the stability of composite amplifiers consisting of a core 2-port amplifier and a lo... more The gain and the stability of composite amplifiers consisting of a core 2-port amplifier and a lossless reciprocal embedding network is studied theoretically with particular interest in the design of near-fmax amplifiers. Design equations for finding an optimal embedding network that gives the highest MAG (maximum available gain) under a given stability requirement are presented. How such an embedding network could be synthesized is briefly sketched.
In this paper, a 1-meter high-speed-wireless data transmission, employing a 300-GHz CMOS RF front... more In this paper, a 1-meter high-speed-wireless data transmission, employing a 300-GHz CMOS RF front end and Cassegrain antennas, is demonstrated. To improve system SNR of the CMOS RF front end, high-gain antennas are designed for the 300-GHz frequency bands. The antenna shows the peak antenna gain of 40 dBi and the 3-dB beamwidth of 1.3 degrees, within the diameter of 6 cm. In the wireless demonstration, the maximum data rate of 36 Gb/s with QPSK modulation is achieved due to high gain antennas.
This paper discusses a sophisticated backend capacitor mismatch characterization technique based ... more This paper discusses a sophisticated backend capacitor mismatch characterization technique based on direct capacitance measurements with a standard C-V meter, wafer prober subsite moves to measure the two capacitors of each pair sequentially and monitor the measurement noise, and statistics to take this noise appropriately into account. We describe requirements, capabilities and limitations of this approach. It is concluded that this technique proves excellently suited for assessing the matching performance of backend capacitors in the most relevant range of 10 fF to 10 pF.
A broadband noise measurement system is newly developed and demonstrated at temperatures between ... more A broadband noise measurement system is newly developed and demonstrated at temperatures between 3 K and 300 K. Using the system, wideband noise spectroscopy (WBNS) from 20 kHz to 500 MHz is carried out for the first time, revealing that shot noise is the dominant white noise down to 3 K. The paper also suggests, by means of WBNS, the possibility of extracting the baseline noise characteristics, which do not include the noise component that varies a great deal from device to device.
We propose a methodology of variable-temperature broadband noise characterization for cryogenic M... more We propose a methodology of variable-temperature broadband noise characterization for cryogenic MOSFETs. A DUT is mounted on a reusable PCB vehicle with a built-in low-noise amplifier, and loaded into a cryogenic chamber. Using the vehicle, we measured flicker (low frequency) and white noise, and have successfully revealed dominance of shot noise in the temperature range from 300 to 120 K for the first time.
IEEE Transactions on Microwave Theory and Techniques, 2023
A signal flow graph (SFG) representation of smallsignal responses of nonlinear microwave circuits... more A signal flow graph (SFG) representation of smallsignal responses of nonlinear microwave circuits around a largesignal operating point is developed using the X-parameters. It is shown that, unlike the SFGs for linear circuits, negativefrequency nodes need to be included explicitly. The development elucidates the circuit-operational meaning of the elusive T-type small-signal X-parameters, which represent the interaction between positive-and negative-frequency components. As an example, such an SFG is used to derive a closed-form expression of the output power of an amplifier as a function of the load reflection coefficient. It is then used to plot approximate loadpull power contours. The result is consistent with the expressions of the optimum load reflection coefficient derived by Root et al. (EuMIC 2017) and power contours derived by Peláez-Pérez et al. (TMTT 2013). SFGs provide an alternative systematic means to derive closed-form expressions in terms of X-parameters and gain illuminating insights into the workings of weakly nonlinear circuits.
A broadband noise measurement system is newly developed and demonstrated at temperatures between ... more A broadband noise measurement system is newly developed and demonstrated at temperatures between 3 K and 300 K. Using the system, wideband noise spectroscopy (WBNS) from 20 kHz to 500 MHz is carried out for the first time, revealing that shot noise is the dominant white noise down to 3 K. The paper also suggests, by means of WBNS, the possibility of extracting the baseline noise characteristics, which do not include the noise component that varies a great deal from device to device.
It is known that designing an LNA for its minimum noise figure (NF) is not the best if the design... more It is known that designing an LNA for its minimum noise figure (NF) is not the best if the design goal is the lowest NF of the entire receiver (RX). A better LNA performance metric is the noise measure (NM). However, if feedback is allowed, the minimum NM can be realized with different combinations of NF and available gain, depending on which the RX NF changes. This paper theoretically studies the low-noise performance limit of an RX when lossless feedback is applied to its LNA. Somewhat counterintuitively, the lowest possible RX NF is shown to be realized when the LNA NM is slightly off its minimum NM. A new noise performance metric, $\Xi$, is introduced. The RX NF is shown to be minimized when $\Xi$ of LNA is minimized. Unlike NM, $\Xi$ is applicable even when the first stage of an RX is passive, as in a passive-mixer-first THz RX.
A physics-based equivalent circuit model of the ceramic capacitor is proposed, which can reproduc... more A physics-based equivalent circuit model of the ceramic capacitor is proposed, which can reproduce frequency characteristics of its impedance including the often observed yet hitherto physically unexplained kinks appearing above the primary series resonance frequency. The model can also account for parasitic effects of external inductances. In order to efficiently analyze and gain engineering insight into ceramic capacitors with a large number of metallic laminae, a two-dimensional method of moments is developed that treats the laminar structure as a uniform, effective medium. It turns out that the primary resonance and the kinks can be well understood and modeled by a lossy transmission line stub with a drastic wavelength reduction. The capacitor model is completed by adding components describing the skin effect and external inductances. The modeled impedance stays within a 4% margin of error up to 5 GHz. The proposed model could greatly improve the accuracy of power distribution network simulation.
Journal of Physics: Condensed Matter, Jul 25, 2000
The effect of a tunnelling electron on the tunnel barrier shape is studied at the limit where a s... more The effect of a tunnelling electron on the tunnel barrier shape is studied at the limit where a static image charge model is applicable. It is shown that the single-electron tunnelling current through an ultrasmall voltage-biased junction is not proportional to the junction area because of charging at the electrodes. Simple expressions are presented for the effective static barrier shape of a voltage-biased junction and of a junction in a circuit, the former of which accounts for the anomalous current scaling. A possible experimental arrangement for verifying the scaling relationship is suggested, with numerical results.
Coulomb blockade devices can circumvent some of the problems that arise from the continuing minia... more Coulomb blockade devices can circumvent some of the problems that arise from the continuing miniaturization of conventional circuits. However, device miniaturization and higher circuit integration aggravate cross-coupling phenomena in Coulomb blockade circuits. As an example, a silicon-based bidirectional electron pump was electrically characterized with emphasis on cross-coupling arising from the clock signal driving the pump. The cross-coupling alters profoundly the expected device characteristics, and the experimental data are confirmed by Monte Carlo simulations.
This paper presents an experimentally found device-size-independent universal relationship betwee... more This paper presents an experimentally found device-size-independent universal relationship between the settling time of floating-body silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) and the substrate current in body-tied devices. Such a relationship could enable one to characterize dynamic properties of SOI MOSFETs through DC measurements and would be useful for physical compact modeling of history effects.
A method of failure analysis is developed based on probability theory. Unlike Monte Carlo methods... more A method of failure analysis is developed based on probability theory. Unlike Monte Carlo methods, it produces accurate results even when the probabilities of interest differ from one another by many orders of magnitude. The method is applied to the analysis of the leakagecurrent distribution of double-gate MOSFETs and the microscopic failure mechanism is identified that limits the final yield. It explains experimental data very well. The insight into the failure mechanism gives clear guidelines for yield enhancement and facilitates device design together with the quantitative yield prediction.
This paper reports a CMOS power amplifier (PA) designed considering the performance degradation o... more This paper reports a CMOS power amplifier (PA) designed considering the performance degradation of MOSFETs caused by both temperature variations and the hot-carrier effect. A small-signal MOSFET model that reproduces the transient degradation caused by the hot-carrier effect is proposed. A 79 GHz CMOS PA was designed utilizing the proposed small-signal model. Simulation results agreed well with the measurement results of the PA fabricated with a 40 nm CMOS technology. It achieved the small-signal gain variations of below 0.7 dB and the OP1dB degradation of less than 0.8 dB in the temperature range of 0°C to 100°C.
The gain and the stability of composite amplifiers consisting of a core 2-port amplifier and a lo... more The gain and the stability of composite amplifiers consisting of a core 2-port amplifier and a lossless reciprocal embedding network is studied theoretically with particular interest in the design of near-fmax amplifiers. Design equations for finding an optimal embedding network that gives the highest MAG (maximum available gain) under a given stability requirement are presented. How such an embedding network could be synthesized is briefly sketched.
In this paper, a 1-meter high-speed-wireless data transmission, employing a 300-GHz CMOS RF front... more In this paper, a 1-meter high-speed-wireless data transmission, employing a 300-GHz CMOS RF front end and Cassegrain antennas, is demonstrated. To improve system SNR of the CMOS RF front end, high-gain antennas are designed for the 300-GHz frequency bands. The antenna shows the peak antenna gain of 40 dBi and the 3-dB beamwidth of 1.3 degrees, within the diameter of 6 cm. In the wireless demonstration, the maximum data rate of 36 Gb/s with QPSK modulation is achieved due to high gain antennas.
This paper discusses a sophisticated backend capacitor mismatch characterization technique based ... more This paper discusses a sophisticated backend capacitor mismatch characterization technique based on direct capacitance measurements with a standard C-V meter, wafer prober subsite moves to measure the two capacitors of each pair sequentially and monitor the measurement noise, and statistics to take this noise appropriately into account. We describe requirements, capabilities and limitations of this approach. It is concluded that this technique proves excellently suited for assessing the matching performance of backend capacitors in the most relevant range of 10 fF to 10 pF.
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Papers by Shuhei Amakawa