7.5 Technology D: Pseudomorphic HEMT on GaAs for X-Band to Ka-Band

Figure 7.33: Output characteristics of a $l_g$= 300 nm AlGaAs/InGaAs HEMT on GaAs substrate.

Technology D is designed primarily to match high-power requirements in X-band (8-12 GHz) to the Ka-band (26.5- 40 GHz).

Figure 7.34: Measured temperature dependence of $g_m$ and $f_T$ for $T_L$= 300-473 K for a $l_g$= 150 nm device.

Fig. 7.33 shows the simulated and measured output characteristics of a pseudomorphic AlGaAs/ InGaAs/ GaAs HEMT with ${\it l}_{\mathrm{g}}$= 300 nm. Scaling the device to ${\it l}_{\mathrm{g}}$= 150 nm allows for high-power applications up to 42 GHz. Fig. 7.34 shows the simulated and measured transconductance ${\mit g}_{\mathrm{m}}$ and ${\it f}_\mathrm{T}$ at ${\it V}_{\mathrm{DS}}$= 5 V for a HEMT with ${\it l}_{\mathrm{g}}$= 150 nm for the temperature range between ${\it T}_\mathrm{L}$= 300 K and ${\it T}_\mathrm{L}$= 473 K. Considering an operational voltage of typically ${\it V}_{\mathrm{DS}}$= 5 V for a high-power device, the limitation of a double recess concept can be seen in Fig. 7.34. Although this device provides extremely high output power levels up to 42 GHz, as shown in Chapter 6, for applications beyond 42 GHz aggressive gate length scaling to ${\it l}_{\mathrm{g}}$= 100 nm [131] is necessary to reduce capacitances. An alternative is the use of single recess devices, such as Technology C, at reduced ${\it V}_{\mathrm{DS}}$ voltage to ensure reliability. A possible alternative under consideration is the metamorphic materials system with well chosen In content, as discussed below, to overcome the gain shortage for f$>$ 42 GHz and to achieve better PAE.