Current limitation after pinch-off in AlGaN/GaN FETs

Applied Physics Letters

et al. 2001

251

134

We report on a metal–insulator–semiconductor heterostructure field-effect transistor (MISHFET) using Si3N4 film simultaneously for channel passivation and as a gate insulator. This design results in increased radio-frequency (rf) powers by reduction of the current collapse and it reduces the gate leakage currents by four orders of magnitude. A MISHFET room temperature gate current of about 90 pA/mm increases to only 1000 pA/mm at ambient temperature as high as 300 °C. Pulsed measurements show that unlike metal–oxide–semiconductor HFETs and regular HFETs, in a Si3N4 MISHFET, the gate voltage amplitude required for current collapse is much higher than the threshold voltage. Therefore, it exhibits significantly reduced rf current collapse.

mentioning

confidence: 98%

Si 3 N 4 / AlGaN/GaN –metal–insulator–semiconductor heterostructure field–effect transistors

Koudymov

Applied Physics Letters

et al. 2001

251

134

“…The so-called current collapse [1][2][3][4] and long-term stability are the most important problems preventing large-scale practical usage of nitride-based heterostructure field-effect transistors ͑HFETs͒ and metal-oxide-semiconductor HFETs ͑MOSHFETs͒ in ultra-high-power microwave systems. The current collapse manifests itself as a reduction of the device current when a large alternating signal is applied to the gate.…”

mentioning

confidence: 99%

Induced strain mechanism of current collapse in AlGaN/GaN heterostructure field-effect transistors

Applied Physics Letters

Koudymov

Tarakji

et al. 2001

112

Gated transmission line model pattern measurements of the transient current–voltage characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs) and metal–oxide–semiconductor HFETs were made to develop a phenomenological model for current collapse. Our measurements show that, under pulsed gate bias, the current collapse results from increased source–gate and gate–drain resistances but not from the channel resistance under the gate. We propose a model linking this increase in series resistances (and, therefore, the current collapse) to a decrease in piezoelectric charge resulting from the gate bias-induced nonuniform strain in the AlGaN barrier layer.

“…A so-called current collapse [26][27][28][29] and long-term stability are the most important problems preventing large-scale practical usage of nitride-based HFETs in ultra-high power microwave systems. The current collapse usually manifests itself as a reduction of the device current when a large RF signal is applied to the gate.…”

Section: Pulsed Return Current Techniquementioning

confidence: 99%

Insulated Gate Iii-N Heterostructure Field-Effect Transistors

Int. J. Hi. Spe. Ele. Syst.

Shur

Gaška

2004

Unique materials properties of GaN-based semiconductors that make them promising for high-power high-temperature applications are high electron mobility and saturation velocity, high sheet carrier concentration at heterojunction interfaces, high breakdown field, and low thermal impedance (when grown over SiC or bulk A1N substrates). The chemical inertness of nitrides is another key property. An AlGaN/GaN Heterostructure Field Effect Transistor (HFET) has been a topic of intensive investigations since the first report in 1991 [1]. Several groups demonstrated high power operation of AlGaN/GaN HFETs at microwave frequencies [2,3,4], including a 100 W output power single chip amplifier developed by Cree, Inc. and devices with 100 GHz cut-off frequency reported in [5]. However, in spite of impressive achievements, the potential of nitride based HFETs has not been fully realized as yet. The RF powers expected from the fundamental properties of nitride based materials significantly exceed the experimental data. One of the key problems limiting the HFETs RF characteristics is high gate leakage currents causing DC and RF parameter degradation. When the gate voltage goes positive the forward leakage current shunts the gate-channel capacitance and thus limits the maximum device current. When the gate voltage is negative, high voltage drop between the gate and the drain causes premature breakdown and thus limits maximum applied drain voltage. In addition, gate leakage currents increase the device sub-threshold currents, which decrease the achievable amplitude of the RF output. These limitations become even more severe at high ambient temperatures. The characteristics of III-N HFETs can be considerably improved by implementing a new approach, which results from the demonstration of good quality of Si0 2 /AlGaN and Si 3 N4/AlGaN interfaces. This approach opens up a way to fabricate insulated gate heterostructure field-effect transistors (IGHFETs), which have the gate leakage currents several orders of magnitude below those of regular HFETs, and exhibit better linearity and higher channel saturation currents. In this chapter, we describe design, characterization and applications of these novel devices.