Noise and Large-Signal Characterization of a Thin-Film MHEMT Feedback Amplifier in Multilayer MCM-D Technology

In this paper, we investigate the noise and large-signal behavior of a feedback amplifier in multilayer thin-film MCMD technology. A small-signal equivalent model (including noise) of the active devive, a thin-film MHEMT, is identified. A large-signal state-space transistor model is built from timedomain data. These models are implemented in a circuit simulator and can accurately predict the noise and large-signal behavior of the feedback amplifier. INTRODUCTION MCM-D technology has proven to be a viable candidate for the integration and interconnection of high-quality microwave and RF applications [1, 2]. Recently, we have shown that thin-film Ge-based metamorphic HEMTs (MHEMTs) can be used in MCM-D circuits [3, 4]. After substrate removal, the MHEMTs (thickness < 3 μm), are embedded in the bottom BCB layer of the MCM-D layer structure. This technique leads to a reduction in interconnection length (between transistor and passive devices), size and weight. Figure 1 shows a schematic cross-section of this combination of III-V and MCM-D technology. Figure 1: Schematic cross-section of integrated passives and embedded Gebased HEMT in MCM-D technology. In this work, we investigate the accuracy of a smallsignal transistor model (including noise) and a large-signal transistor model for a thin-film MHEMT. The noise figure and large-signal behavior of the amplifier can be predicted accurately. TRANSISTOR MODELING The small-signal equivalent transistor model (including noise) is extracted using S-parameter measurements. The noise parameters are determined using the F50 method [5]. The noise parameters can be directly obtained from the frequency variation of the noise figure F50 corresponding to a 50 Ω generator impedance. This method has the following advantages: • no need for an automatic input tuner; • well suited for measurements in the mm-wave range. The NFmin (minimum noise figure) of a thin-film MHEMT is higher than the NFmin of a comparable GaAs MHEMT due a higher channel temperature in the thin devices (see figure 2). 10 20 30 40 0 50 2 4