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Entropy is producing during any irreversible process. In the cancer cells, the entropy generation measures the irreversibility; so, the cancer cells have higher entropy generation than the healthy cells. The entropy generation rate shows the amount of robustness, progression, and invasion of the cancer cells. From a thermodynamic aspect, cancer's origin and growth is an irreversible process, and the thermodynamic variables such as the cell volume, temperature, and entropy will change during this process. In this paper, a procedure based on experimental data is proposed to calculate dynamic entropy generation in the tumoral tissues by dynamic thermography and measurement of tumor size. The dynamic changes in the volume, temperature, and entropy associated with tumor cells over time are tested and evaluated in this regard. An in vivo assay has been developed to measure and analyze these changes. This assay investigated the growth of 4T1 Breast Tumor in 55 BALB/c mice over time. Infrared thermography has been employed to evaluate dynamic temperature changes of the tumors. The computer code has been developed to gather important data from tumoral and healthy mice's images to compute considered temperature differences and entropy generation associated with tumoral tissues. To better evaluate tumor tissue, the Micro PET Images are used to verify volume changes of tumors. The relation between the volume and temperature gradient of tumor cells has detected by measuring during the experiment. The entropy of tumor cells was studying and calculating during the process of tumor changes. Results show that entropy generation as the main concept of thermodynamic is a strong tool for the analysis of cancer cells and has a strong relationship with cancer growth.

The key objective of this study is to investigate the local mismatch of pre and post multilayer structure on the active devices. Five pre and post multilayer structure pHEMTs on the same wafer within the same cell between adjacent devices are considered. As the study of local mismatch ensures good yields and a way to gain insights about the technology various comparisons are made including the effects of multilayer structuring. The threshold voltage, built-in potential and the net doping concentration of the 2-DEG of the devices are extracted through capacitance-voltage data. The underlying electrical parameter of the transistors as well as the RF figure of merit has been analyzed. The microwave noise related parameters namely minimum noise figure, associate gain, noise resistance, magnitude of the optimum reflection are also discussed and investigated. Centre-to-edge mismatch results in minor variation in performance between devices. These studies would help within the advancement of solid, proficient and low cost generation of future compact structure in 3-D multilayer MMICs.

International audience; The microwave noise Figure modelling for AlGaN/GaN HEMTs is shown in this study over a large range of temperatures e.g., -40 to 150°C. Standard noise parameters for example minimum noise Figure NFmin), normalized noise equivalent resistance Rs, and association gain Ga were modelled at various frequencies and temperatures. The temperature coefficients of noise-related equivalent circuit parameters (ECPs) were also determined. The noise parameters of GaN on SiC based HEMTs are considered to be analogous to GaN HEMTs on Si, sapphire, and diamond substrates, as well as InP- and GaAs HEMTs. According to the findings, GaN/SiC HEMTs offer a lot of potential for applications requiring LNAs at high temperatures.

Thermal effect on intermodulation distortion (IMD) behavior of GaN based high-electron mobility transistor (HEMT) have been researched over input power and frequency using a two-tone technique. A significant modification was observed in terms of magnitude on the linear component and the magnitude as well as the position and appearance of the nulls/notches of the nonlinear components was changed conspicuously. The parasitic resistances and as well as the output current were affected when applied input power increases. As a result, an increase in the output IMDs found and the device threshold voltage VT moves towards more negative of Vgs trace which in turn shifts the notch points of the nonlinear IMDs towards lower values of applied bias Vgs. The values of the output IMDs degrades with the increment of temperature and frequency. The output IMD products also reduced following the transconductances response to temperature. On the other hand, the notch/null's position of the nonlinear IMDs also moves following the thermal response of threshold voltage. This authentic and exhaustive study is crucial to figure out the minimum distortion, maximum gain bias option for active devices.

International audience; Taylor Series coefficients (TSCs) are one of the main factors behind the device's nonlinearity. Mull-bias behaviour of TSCs for GaN HEMT has been extracted using two-tone technique. To extract the higher-order TSCs of the output current, two-tone intermodulation distortion (IMD) measurement along with properly designed load impedance is used at low frequency (50 and 51 MHz) for the accurate prediction of the cross-term derivatives. For the extraction of TSCs of the nonlinear output current, Volterra series analysis is utilized for the accurate reproduction of the harmonic component. Finally, the verification between the measured and simulated IMD products shows good agreement. This simple and straightforward method is utilized successfully for nonlinearity analysis.

International audience; This work notices the relation among the kink effect and the mobility in AlGaN/GaN HEMT and its response to temperature. The kink phenomenon found in transistor behaviour are carefully characterized at persuade point which is straightaway linked to the shallow traps positioned underneath the conduction band. A straightforward relationship among parasitic impacts within the output properties and the existence of deep levels or traps would demonstrate by a temperature-dependent mobility model. This study helps to predict the location of kink voltage in terms of gate bias near to the threshold voltage and also emphasize the impact of the mobility scattering. In expansion, the traps states for GaN HEMT grown on SiC substrate and their related activation energy based on existing literature also summarized.

Detailed analysis of device behaviour on the zero-temperature coefficient (ZTC) points for microwave GaAs based high-electron mobility transistor is presented by means of on-wafer measurements over the temperatures between −40 and 150 °C. This zero temperature coefficient points found not only in the transfer and transconductance curve but also in intrinsic transconductance g mo , output conductance g ds , small signal gain S 21 , and minimum noise figure NF min also exhibits ZTC. It is found that the zero temperature coefficients points are impacted by both threshold voltage and drain bias. The transfer current base, ZTCI ds moved from 0.1 V to −0.2 V of V gs trace and transconductance based, ZTCg m moved from −0.3 V to −0.6 V of V gs trace with the drain bias, V ds varies from 1 V to 5 V. The behaviour of some intrinsic equivalent circuit parameters along with cut-off frequency, f t at both ZTC bias points opens some crucial insight and opportunities in microwave device design for low and high temperature applications.

Linear and nonlinear characteristics of a 0.5 μm × (2 × 100) μm gate double heterojunction AlGaAs/InGaAs/GaAs pseudomorphic high-electron mobility transistor have been investigated using a two-tone intermodulation distortion (IMD) measurement technique. The results indicate a significant modification on the IMD output power components such as fundamental, IMD2, IMD3, IMD4, IMD5 and IMD7 with the variation of biasing conditions, input power, frequency and temperature. Increase in input power affects the output current as well as the parasitic resistances and subsequently the threshold voltage reduces, resulting to an increase in the output IMD power. On the other hand, increase in frequency & temperature reduces the magnitude of the output IMDs. The temperature affects the output current as well as the parasitic resistances and the threshold voltage, results a decrease in the output IMD power. The threshold voltage shifts negatively with temperature and modifies the notch/null’s position of the second and higher order IMD output power components. This investigation is valuable for the circuit designers to evaluate the best biasing option in terms of minimum distortion, maximum gain for future design optimizations.

This study focuses on 3-D multilayer monolithic integration of vertical-oriented double-heterojunction AlGaAs/InGaAs/GaAs based pseudomorphic high electron mobility transistors. The effects of the presence of 3-D components above the active layer were accomplished by comparing three multilayer fabricated device of different thickness with a virgin device where the thickness of the 3-D components e.g., both metal and polyimide layer were varied. The output current, on-state gate leakage, transconductance are found to be decrease with the increase in thickness of the 3-D components and on the other hand, the on-state resistance, knee voltage and off-state gate leakage is increased. Lastly, the thermal influences on the device behaviour such as off-state and on-state gate leakage, barrier inhomogeneities at Schottky contacts, zero temperature coefficients at the transfer curve, and the threshold voltage as a function of drain bias were measured and analyzed for the both pre and post fabricated multilayer devices. These effective comparisons in terms of thickness and temperature of the both device are useful for future designs and optimizations of multilayer vertical stacked 3-D MMICs.

Temperature influence on the device behavior has been carried out on AlGaAs/InGaAs/GaAs-based pseudomorphic high-electron mobility transistor fabricated in multilayer 3-D monolithic microwave integrated circuits technology over multibias operation condition. The multibias thermal effect on the dc and RF, small-signal (up to 40 GHz) and large-signal parameters, including the third-order intercept points as well as the linear and third-order intermodulation output power performance at 4 GHz were analyzed and reported for the first time. In addition, the noise figure parameters of device have been reported and estimated at 10 GHz. The temperature coefficients of the device dc and RF parameters are carefully established at the peak transconductance condition. The results are important for the design optimizations of advanced monolithic multilayer integrations.

Multibias and thermal characterizations on 0.25 μm × (2 × 100) μm AlGaN/GaN/SiC HEMT and 0.5 μm × (2 × 100) μm AlGaAs/InGaAs pseudomorphic HEMT have carried out for the first time. Two competitive device technologies are investigated with the variations of bias and temperature in order to afford a detailed realization of their potentialities. The main finding includes the self heating effect in the GaN device, zero temperature coefficient points at the drain current and transconductance in the GaAs device. The thermal resistance RTH of 7.1, 8.2 and 9.4 °C mm/W for the GaN device was estimated at 25, 75 and 150 °C respectively which are consistent with those found in the open literature. The temperature trend of the threshold voltage VT, Schottky barrier height ϕb, sheet charge densities of two dimensional electron gas ns, and capacitance under the gate Cg are exactly opposite in the two devices; whereas the knee voltage Vk, on resistance Ron, and series resistance Rseries are shows similar trend. The multi-bias and thermal behavior of the output current Ids, output conductance gds, transconductance gm, cut-off frequency ft, maximum frequency fmax, effective velocity of electron, veff and field dependent mobility, μ demonstrates a great potential of GaN device. These results provide some valuable insights for technology of preference for future and current applications.

International audience; This paper investigates the correlation between intermodulation distortion and RF transconductance in AlGaN/GaN high electron mobility transistor (HEMT) grown on SiC Substrate. Two-tone intermodulation distortion measurements were carried out across a comprehensive biasing range changing the frequency and ambient temperature and input power to point out this correlation. The main contribution is that, the correlation between intermodulation distortion and the behavior of transconductance and its derivatives (Gm, Gm2, and Gm3) is investigated and summarized. It is demonstrated that the nonlinearity is directly correlated to the RF transconductance behavior where the peak values of the fundamental IMD arise at the peak of Gm and the null points in IMD2 and IMD3 arises when Gm2 and Gm3 alters from positive to negative magnitudes. The changes in frequency, input power and temperature affect the threshold voltage VT which in turn impacts on that phenomenon. As the nulls/notches are crucial indicator for identifying minimum distortion level, an empirical model for null's current is develop in correlation with transconductance. Finally, the measured and simulated IMDs as well as the null's current shows very good agreement. In addition, the small-signal measurement and as well as the de-embedding of the device has been done before the IMD study. The power gain and its derivatives also compared to the transconductance. This analysis is important to know how the intermodulation distortion products behave and to identify a distortion free device at the particular operation point of interest.

Thermal characterizations and modeling have been carried out on a $0.15~\mu \text{m} \,\, \times $ ( $4 \times 50$ ) $\mu \text{m}$ gate GaN-/SiC-based high-electron-mobility transistor varying the temperature from −40 °C to 150 °C and the frequency up to 50 GHz using on-wafer measurements. The thermal behavior of the dc parameters along with thermal resistance estimation and the equivalent circuit parameters along with cutoff and maximum frequencies were analyzed and reported using a single device. The temperature coefficients of these parameters were presented and deduced the influence of thermal effects on device parameters. These results are important for the circuit designer for future advancement and design optimizations of GaN-based monolithic microwave ICs.

Thermal and small-signal model parameters analysis have been carried out on 0.5 μm × (2 × 100 μm) AlGaAs/GaAs HEMT grown on semi-insulating GaAs substrate and 0.25 μm × (2 × 100 μm) AlGaN/GaN HEMT grown on SiC substrate. Two different technologies are investigated in order to establish a detailed understanding of their capabilities in terms of frequency and temperature using on-wafer S-parameter measurement over the temperature range from −40 to 150 °C up to 50 GHz. The equivalent circuit parameters as well as their temperature-dependent behavior of the two technologies were analyzed and discussed for the first time. The principle elevation or degradation of transistor parameters with temperature demonstrates the great potential of GaN device for high frequency and high temperature applications. The result provides some valuable insights for future design optimizations of advanced GaN and a comparison of this with the GaAs technology.

Temperature-dependent dc and small-signal analysis have been carried out on $0.5~\mu \text{m} \,\, \times \,\, 200$ - $\mu \text{m}$ AlGaAs/InGaAs pseudomorphic high-electron mobility transistor over the temperature range from −40 °C to 150 °C by on-wafer S-parameter measurements up to 50 GHz. The thermal behavior of dc and equivalent circuit parameters along with their temperature coefficients was analyzed and reported for the first time using the same device. Most of these parameters show a negative trend with temperature, such as drain–source output current $I_{\mathrm{ ds}}$ , extrinsic transconductance $g_{m}$ , effective electron velocity ${v}_{\mathrm{ eff}}$ , threshold voltage $V_{T}$ , Schottky barrier height $\phi _{b}$ , gate–drain capacitance $C_{\mathrm{ gd}}$ , drain–source capacitance $C_{\mathrm{ ds}}$ , intrinsic transconductance $g_{\mathrm{ mo}}$ , cutoff frequency $f_{t}$ , and maximum frequency $f_{\mathrm{ max}}$ . On the other hand, Two-dimensional electron gas sheet carrier density $n_{s}$ , ON-resistance $R_{\mathrm{\scriptscriptstyle ON}}$ , series resistance $R_{\mathrm{ series}}$ , terminal resistances ( $R_{g}$ , $R_{s}$ , and $R_{d})$ , output resistance $R_{\mathrm{ ds}}$ , input resistance $R_{i}$ , gate–source capacitance $C_{\mathrm{ gs}}$ , and intrinsic delay time $\tau $ show a positive trend with temperature. The results provide some valuable insights for future design optimizations of advanced GaAs-based Monolithic microwave integrated circuits.

Investigation of the third-order intercept point, IP3 and nonlinear distortion level, NDL for pre-and post-multilayer processed GaAs pHEMTs has been accomplished by employing two-tone intermodulation distortion measurements. The third-order intercept point is a biasing, input power, frequency-dependent term, particularly related to the fundamental and third-order intermodulation distortion component and the study extended from low to high temperatures. The main findings are that the output referenced OIP3 decreased while the input referenced IIP3 increased with frequency at peak transconductance condition and the study further extended to multi-bias operation condition. Within the measured temperature range, the IP3 and NDL modified significantly following the behaviour of IMD3 distortion. This investigation of IP3 is utilized to measure how much distortion is created and referring this to the antenna input gives a straightforward strategy to decide whether or not the spec can be met. On the other hand, analysis of NDL is vital for choosing the most excellent biasing alternative with the entryway measurements of the device to create a compromise agreeing to the desired utilization.

This paper investigates the design, fabrication, testing of Ni-Cr based thin film resistors (TFRs) with 80:20 ratio is fabricated on a 2-inch GaAs wafer for monolithic microwave integrated circuits (MMICs) applications. For the purpose of assessing the Ni-Cr thin film resistors performance in 3-D MMICs, five resistors having size of 0.5, 1, 2, 4 and 8 squares and thickness of 30 nm each from five distinctive groups were measured. All the TFRs are measured with and without polyimide on top of these resistors. The TFRs with polyimide exhibits a minor increase in resistance value which is possibly due to the oxidation process during the curing of two layers of polyimides. On the other hand, great temperature solidness has been watched over the temperature examined and a greatest TCR of 60ppm/oC is achieved from room temperature to 150oC.

This study deals with the uniformity investigation and comparison on the typical behaviour of pseudomorphic high electron mobility transistors (pHEMTs) before and after the 3-D multilayer fabrication. There are seven multilayer fabricated pHEMTs compared with the seven virgin pHEMTs based on drain-source input current, output current, transconductance, off state leakage behaviour, threshold voltage, knee voltage, on-resistance, Schottky barrier height, ideality factor, reverse saturation current, small signal gain and current gain. Below 10% changes in performance can be seen after multilayer fabrication compare to virgin samples and apart from these exceptions, the discrepancies are well within the tolerance and less than 3% in terms of Schottky behaviour. We show that, the application of the 3D-MMIC technology does not cause any visible destruction of pHEMTs performance using seven different samples before and after the multilayer fabrication.

Detailed study of zero temperature coefficients (ZTC) for microwave GaAs and GaN based high electron mobility transistors were reported and analysed. The measured temperature-dependent data between −40 to 150°C were observed of transconductance and drain current for the both devices. It was found that the variation of threshold voltage (V T) with the drain bias (V ds) has an influence on zero temperature coefficient points. Furthermore, the drain current based ZTC point arises before VT for GaN and after VT for GaAs FETs with respect to drain bias. Inconsistency are observed; most conspicuously that the temperature trends of the threshold voltage for these two device technologies are utterly contrasting. In addition, transconductance based ZTC is absent in GaN device. Furthermore, the effective mobility is estimated using an improved model for the GaN device. The results indicate a well-confined 2-DEG with high mobility as the peak value of effective mobility closely corresponds with the Hall mobility. This work provides some worthwhile insights in microwave circuits design for high temperature applications.

International audience; The main aim of this article is to present an experimental analysis of the thermal influence on the positive derivatives of the real parts of impedance parameters against frequency (PDRZ) for microwave GaN and GaAs based HEMTs. The PDRZ effect is investigated with respect to temperature by both heating and cooling the studied devices. The main findings are that both devices are affected by the PDRZ effect, although with different severity and onset frequency. Due to the extrinsic resistances response with temperature, the real parts of impedance parameters shift towards higher values, especially for the GaAs HEMT. By de-embedding appropriate values of the extrinsic capacitances, the PDRZ effect can be neutralized in both devices. As the extrinsic capacitances are thermally unresponsive, roughly the same values of the extrinsic capacitances are achieved for all the studied temperatures.

Photoresponse of GaAs-based double-heterojunction phototransistors (DHPTs), in surface-illuminated orientation, has been analyzed with a modified small-signal model. The effect of incident optical illumination on various intrinsic parameters has been discussed for In0.49Ga0.51P/GaAs N+p+N− DHPT. Since the primary detecting material is GaAs, the device is optimized to detect short wavelength at 850 nm. A novel formulation for optical flux absorption in DHPTs is also provided along with its comparison with single-heterojunction phototransistors. The analysis of DHPTs presented in this paper can be utilized for performance enhancement through device optimization in sensors, photoreceivers in optical networks, and remote sensing applications employing integrated circuits.

The anomalies and the threshold voltage shifts in GaN and GaAs based high electron mobility transistors over temperature were reported and analyzed using on wafer measurements. Discrepancies are noticed; most conspicuously that the thermal trends of the threshold voltage of the two device technologies are utterly contrasting. This anomaly extends for the other parameters of the devices such as sheet carrier densities of the two-dimension electron gas. In addition barrier inhomogeneities and the band offset of the semiconductor heterojunction with temperature provides some valuable insights between the two competitive device technologies.

The main aim of this paper is to investigate the uniformity of pHEMTs small-signal parameters before and after multilayer fabrication in 3-D MMICs. Seven samples of pre-and post-multilayer fabricated pHEMTs at different representative locations to reflect the degree of consistency. This study deals with the fabrication, measurement, simulation, and comparison of both sample in form of means and slandered deviation. On wafer scattering (S-) parameter measurement has been accomplished to investigate the small signal equivalent circuit parameters up to 50 GHz. The main finding was observed that all parameters are increased after multilayer fabrication except the transconductance and the parasitic inductances. The employment of the 3D-MMIC technology does not induce any evident extinction of the pHEMTs performance utilizing seven different samples of pre-and post-multilayer fabrication.

International audience; AbstractThermal influence on S22 kink behavior has been carried out on a 0.15 μm gate length AlGaN/GaN/SiC high electron mobility transistor over a wide range of temperature. The size and the shape of the S22 kink effect (KE) in terms of biasing and temperature have been evaluated. The main finding is that S22 of the studied device is affected by two kinks: the first one appears at approximately 19 GHz and then the second one appears at about 43 GHz. The impact of the intrinsic circuit parameters on the S22 kink phenomena is inspected to assess their contribution. In addition, a new procedure is proposed to quantify this type of phenomenon by defining the kink area as the area between the two curves corresponding to S22 with and without the KE. The relevance of this study emerges from the fact that an exhaustive characterization of these anomalous phenomena can empower RF engineers to effectively take them into account for both modeling and design purposes.

In this paper, the development and implementation of vertical-oriented monolithic microwave ICs (MMICs) in Schottky diode structure are discussed. The Schottky diode is configured by shorting the drain and source contacts of a prefabricated pseudomorphic HEMT (pHEMT) in vertical arrangement to minimise the utilisation of chip area. Smaller forward voltage drop is observed from the Schottky diode which designed for microwave rectification. Measured S-parameters show good agreement with the simulated analysis. To investigate the feasibility of this approach, the Schottky diode is used in designing a limiter circuit. A very low insertion loss of less than 1.89 dB is observed at 3 GHz. It is also revealed the ability of limiter circuit to block high power level signal at 20 dBm of input power. This vertical-oriented approach provides promising solution to the integration of active and passive components in MMIC on a single chip.

In this paper, we report anomaly and intrinsic capacitance behaviour over temperature of AlGaN/GaN/SiC and AlGaAs/GaAs high electron mobility transistors using on wafer measurement up to 50 GHz. Differences are observed; most notably that the trend of the intrinsic capacitances behaviour with temperature of the two device technologies are completely different. This anomaly continues for the other device parameter such as threshold voltage, two-dimension electro gas sheet carrier densities as well. These results are valuable for the future design optimizations of the advanced GaN and GaAs based monolithic microwave integrated circuit operating at high frequency and temperature.

A microwave receiver protection limiter circuit has been designed, fabricated and tested using vertically stacked GaAs MMIC technology. The limiter circuit with a dimension of 2.5 × 1.3 mm2 is formed by using double-channel AlGaAs/InGaAs pseudomorphic HEMT (pHEMT) Schottky diodes integrated with a low-loss V-shaped coplanar waveguide multilayer structure. The electrical parameter characteristics of the pHEMT Schottky diodes are presented including the C–V profile showing the presence of a double channel in the device layer structure. This unique feature can also be seen from the double-peak responses of the electron density as a function of the device layer width, which represent the high electron concentration at two different 2-DEG layers of the structure. An equivalent circuit model of pHEMT Schottky diodes is demonstrated showing good agreement with the measurement results. At zero-bias condition, the devices show high performance in diode detector applications with voltage sensitivities of more than 89 mV μW−1 at 10 GHz and at least 5.4 mV μW−1 at 35 GHz. The measurement results of the limiter circuit demonstrated the blocking of input power signals greater than 20 dBm input power at 3 GHz. To the best of our knowledge this is the first demonstration of the use of pHEMT Schottky diodes in microwave power limiter applications.

We analyze an analytical spectral-response model for heterojunction phototransistors (HPTs) in order to understand the behavior of lattice-matched InPZIn0.47Ga0.53As HPTs with changing device and material parameters. The preliminary modeling of the spectral response lead to a good agreement between theoretical and experimental results for incident wavelength radiations at 980, 1310, and 1550 nm. We then performed several simulations in order to determine the individual influences of several parameters, such as the base-layer thickness and the surface-recombination velocity on the responsivity of the device. A decreasing trend for the surface-recombination parameter with increasing wavelengths was observed, and it is attributed to the greater recombination rate for high-energy photons generated near the surface.

New electromagnetic modeling technique using 3D momentum optimization has been developed to accurately model compact multilayer coplanar waveguide (CPW) MMICs. Suitable layout simulation setups are provided which showed good agreements with the measured data. Furthermore, a TOM3 schematic design of a MMIC GaAs pHEMT has been developed and compared with its TOM3 netlist file along with the measured results. The fabricated multilayer MMIC amplifier has also been characterized and compared with the simulation data. In addition, we demonstrate the utilization of the optimized amplifier model in understanding parasitic inductance in the on-wafer measurement.

An optically generated kink observed in the Gummel plot of AlGaAs/GaAs single heterojunction phototransistors (sHPTs) is reported when illuminated with relatively high optical powers. The observed sudden rise in collector current and decrease in the base current, referred to as `optical kink effect', is carefully studied and analyzed. The measurements are performed for incident optical power of up to 225 μW at an incident wavelength of 635 nm. This rise in the current gain of HPTs, in three terminal configuration, is associated with the base-collector space-charge modulation similar to the kirk effect.

Spectral response (SR) and optical characteristics of GaAs-based heterojunction phototransistors (HPTs) have been successfully predicted for the first time through an advanced absorption model presented in the present article. The model is based on the accurate prediction of photocarriers in the active layers of the phototransistor which, when related to the base current of transistor in forward active mode, enables the prediction of optical characteristics. The importance of collection efficiency in accurate SR modelling is highlighted and it is not considered unity like all the previous studies on HPTs. The layer dependence of the optical power absorption profile at near-bandgap wavelengths is also investigated and its generalisation as a single exponential has been refuted for GaAs-based HPTs. The measured results at 635, 780 and 850 nm show good agreement to the predicted results, validating the proposed theoretical model.

Low characteristic impedance coplanar waveguide (CPW) interconnects are desirable for microwave applications such as power FET's and photodiodes. In conventional planar MMICs, typical characteristic impedances are in the range of 40-100Ω, such that in order to realize 20Ω interconnect, one has to fabricate a very narrow slot width with a wider signal conductor width. As the objective is to achieve low characteristic impedance interconnects (

Realising the theoretical electrical characteristics of components through modelling can be carried out using computer-aided design (CAD) simulation tools. If the simulation model provides the expected characteristics, the fabrication process of Monolithic Microwave Integrated Circuit (MMIC) can be performed for experimental verification purposes. Therefore improvements can be suggested before mass fabrication takes place. This research concentrates on development of MMIC technology by providing accurate predictions of the characteristics of MMIC components using an improved Electromagnetic (EM) modelling technique. The knowledge acquired from the modelling and characterisation process in this work can be adopted by circuit designers for various high frequency applications.

This paper investigated the temperature effects on the performance of the AlGaN/GaN high electron mobility transistor (HEMT) with a 150 nm and 250 nm gate length on a SiC substrate over a temperature range of −40 to 150 °C including experimental characterization, modelling and analysis by on-wafer measurements up to 50 GHz. All the DC and small signal parameter variations with ambient temperature on the same set of devices have been reported for the first time. The temperature coefficient of all the DC and small signal parameters as well as ft and fmax were reported. Some of the extracted equivalent circuit parameters with the theoretical data of the evolution of electrical parameters and the relevant physical equations involved have been compared using the same biasing condition for further accuracy. The theoretical results are shown to be consistent with the extracted data. Some results are also experimentally verified with previous works cited in the paper. The results provide some valuable insights for the underlying physics of the device parameters affected by temperature.

0.25 μm gate AlGaN/GaN/SiC HEMT's nonlinearity modelling and characterization over a wide temperature and frequency have been studied for the first time. The nonlinearity of these devices has been carried out using a two-tone intermodulation distortion. An empirical analytical model has been developed and good agreement was established between the simulated and measured data. This result is valuable for the future design optimizations of the advanced GaN based MMIC's operating at high temperature.

We report on the device considerations and discuss the design and fabrication of 0.5 μm gate length double-channel GaAs pHEMT well-suited for diode based limiter applications. I-V, C-V and RF characterisations of GaAs pHEMT Schottky diode that is used in the limiter applications have been presented. The presence of double channel is discussed and clearly observed from the doping curve of 1/C2 versus V plot. Double channel layers provide wide-ranging usages in linear application. Based on the measured DC and RF parameter extractions, an equivalent circuit model of the pHEMT Schottky diode is derived. All six unknown model parameters are extracted using direct parameter extraction method. The measured results show good agreement with the modelled over the frequency range from 0 to 40 GHz for operation bias range.

Linear and nonlinear characteristics of 0.25 µm AlGaN/GaN HEMT grown on SiC substrate have been studied as a function of biasing, input power, frequency and temperature using a two-tone intermodulation distortion measurement technique for the first time. The results indicate a significant modification on the output IMD power. An empirical analytical model has been developed and good agreement was shown between the measured data with the simulation results. The analysis of GaN HEMT presented can be utilized for performance enhancement of the design optimization of advanced GaN based MMIC's operating at high temperature.

We report for the first time, the design and realization of a MMIC power limiter based on (0.5 × 200) µm2 pHEMT Schottky diodes using an in-house 3D GaAs multilayer CPW technology. The system of three layers of conductor metals and two layers of sandwich polyimide as dielectric was employed. The limiter design consists of a 50Ω V-shaped coplanar waveguide transmission line connected to a pair of shunt GaAs pHEMT diodes. Measured on-wafer S-parameter data demonstrates a maximum small signal insertion loss of less than 2 dB from 50 MHz to 3 GHz and a return loss better than 7.5 dB.