Kohki Hikosaka

Pseudomorphic In/sub 0.52/Al/sub 0.48/As/In/sub 0.7/Ga/sub 0.3/As HEMTs with an ultrahigh f/sub T/ of 562 GHz

We fabricated decananometer-gate pseudomorphic In/sub 0.52/Al/sub 0.48/As/In/sub 0.7/Ga/sub 0.3/As high-electron mobility transistors (HEMTs) with a very short gate-channel distance. We obtained a cutoff frequency f/sub T/ of 562 GHz for a 25-nm-gate HEMT. This f/sub T/ is the highest value ever reported for any transistor. The ultrahigh f/sub T/ of our HEMT can be explained by an enhanced electron velocity under the gate, which was a result of reducing the gate-channel distance.

547-GHz f/sub t/ In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As HEMTs with reduced source and drain resistance

We fabricated 30-nm gate pseudomorphic channel In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As high electron mobility transistors (HEMTs) with reduced source and drain parasitic resistances. A multilayer cap structure consisting of Si highly doped n/sup +/-InGaAs and n/sup +/-InP layers was used to reduce these resistances while enabling reproducible 30-nm gate process. The HEMTs also had a laterally scaled gate-recess that effectively enhanced electron velocity, and an adequately long gate-channel distance of 12nm to suppress gate leakage current. The transconductance (g/sub m/) reached 1.5 S/mm, and the off-state breakdown voltage (BV/sub gd/) defined at a gate current of -1 mA/mm was -3.0 V. An extremely high current gain cutoff frequency (f/sub t/) of 547 GHz and a simultaneous maximum oscillation frequency (f/sub max/) of 400 GHz were achieved: the best performance yet reported for any transistor.

Selective Dry Etching of AlGaAs-GaAs Heterojunction

Selective dry etching of GaAs to AlxGa1-xAs (x=0.3) using an etching gas composed of CCl2F2 and helium was studied. Etching was carried out at gas composition ratios of PCCl2F2 /PHe above 0.25, total pressures of 0.5 to 5.0 Pa, and power densities of 0.18 to 0.53 W/cm2. A high selectivity ratio exceeding 200 and a clean etch profile were obtained at a gas composition ratio of PCCl2F2 /PHe=1 operated at 5 Pa and 0.18 W/cm2. The etched profile of GaAs under the above conditions exhibited a nearly vertical-wall character.

High Electron Mobility Transistor Logic

A high electron mobility transistor (HEMT) logic is described. Ring oscillators with enhancement-mode switching and depletion-mode load HEMTs with a 1.7 µm-gate length have been fabricated to assess logic performance capability. Switching delays down to 56.5 ps at room temperature and down to 17.1 ps at liquid nitrogen temperature have been obtained. The switching delay of 17.1 ps is the lowest of all the semiconductor logic technologies reported thus far.

Ultra-short 25-nm-gate lattice-matched InAlAs/InGaAs HEMTs within the range of 400 GHz cutoff frequency

We have succeeded in fabricating ultra-short 25-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates. The two-step-recessed gate technology and low temperature processing at below 300/spl deg/C allowed the fabrication of such ultra-short gates. DC measurements showed that the 25-nm-gate HEMT had good pinchoff behavior. We obtained a cutoff frequency f/sub T/ of 396 GHz, within the range of 400 GHz f/sub T/, for the 25-nm-gate HEMT. This f/sub T/ is the highest value get reported for any type of transistor, and the gate length of 25 nm is the shortest value ever reported for any compound semiconductor transistor that exhibits device operation.

Ultrahigh-speed pseudomorphic InGaAs/InAlAs HEMTs with 400-GHz cutoff frequency

An excellent cutoff frequency (f/sub t/) as high as 400 GHz was successfully realized in 45-nm-gate pseudomorphic InGaAs/InAlAs high electron mobility transistors (HEMTs). An additional vertical gate-recess suppressed short-channel effects, while keeping good pinchoff characteristics. Gate length (L/sub g/) dependence of electron transit time (/spl tau//sub transit/) implied an increased saturation velocity (/spl upsi//sub s/) of 3.6/spl times/10/sup 7/ cm/s in the developed pseudomorphic HEMTs. This f/sub t/ is the highest value ever reported for any transistors to date.

Non-Recessed-Gate Enhancement-Mode AlGaN/GaN High Electron Mobility Transistors with High RF Performance

We fabricated non-recessed-gate enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) with a gate length Lg of 120 nm. As gate metals, Ni/Pt/Au and Mo/Pt/Au were used. The Ni/Pt/Au-gate HEMTs with rapid thermal annealing (RTA) at 500°C were normally-off at a gate-source voltage Vgs of 0 V, indicating E-mode operation. Moreover, the Mo/Pt/Au-gate HEMTs also showed E-mode device operation without RTA. The fabricated E-mode HEMTs with both gate metals showed high RF performance. We obtained a cutoff frequency fT of more than 50 GHz and a maximum oscillation frequency fmax of approximately 100 GHz.

Enhancement-Mode High Electron Mobility Transistors for Logic Applications

Enhancement-mode high electron mobility transistors (E-HEMTs) with selectively doped GaAs/n-AlxGa1-xAs heterojunction structures grown by molecular beam epitaxy are described. E-HEMTs with 2- µm long gates have exhibited the square-law drain characteristic. The device has a gm of 409 mSmm-1 of gate width at 77 K and 193 mSmm-1 at 300 K. This value of gm at 77 K is the highest in all field effect devices reported thus far.

Extremely High-Speed Lattice-Matched InGaAs/InAlAs High Electron Mobility Transistors with 472 GHz Cutoff Frequency

We report extremely high-speed 30-nm-gate InGaAs/InAlAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates with a record cutoff frequency ft of 472 GHz, the highest value yet reported for any transistor. The ft value exceeds 450 GHz and 400 GHz even for 50-nm-gate and 70-nm-gate devices, respectively. This outstanding performance is attributed to the significantly increased gm achieved by reducing the lateral gate-recess length while maintaining a small gate-to-channel separation, which enhances the average electron velocity under the gate.

Current-gain cutoff frequency comparison of InGaAs HEMTs

The current-gain cutoff frequency performance of pseudomorphic InGaAs/AlGaAs (20% InAs composition) high-electron-mobility transistors (HEMTs) on GaAs is compared to that of lattice-matched InGaAs/InAlAs HEMTs on InP. The current-gain cutoff frequency (f/sub t/) characteristics as a function of gate length (L/sub g/) indicate that the f/sub t/-L/sub g/ product of approximately 26 GHz- mu m in InGaAs/InAlAs HEMTs is 23% higher than that of approximately 21 GHz- mu m in InGaAs/AlGaAs HEMTs. The performance of InGaAs/AlGaAs HEMTs is also 46% higher than that of conventional GaAs/AlGaAs HEMTs ( approximately 18 GHz- mu m). These data are very useful in improving the device performance of HEMTs for a given gate length.<<ETX>>