Improved Electrical Performance and Thermal Stability of HfO[sub 2]/Al[sub 2]O[sub 3] Bilayer over HfO[sub 2] Gate Dielectric AlGaN/GaN MIS–HFETs

Abstract

AlGaN/GaN metal–insulator–semiconductor heterostructure field-effect transistors (MIS–HFETs) with a HfO2/Al2normalO3 bilayer gate dielectric have been fabricated, characterized, and compared with HfO2 gate dielectric MIS–HFETs. Physical and electrical characterizations have revealed the enhanced properties of the HfO2/Al2normalO3 bilayer dielectric over that of the single HfO2 layer. As a result, the fabricated HfO2/Al2normalO3 MIS–HFETs exhibit better electrical performance and thermal stability than the HfO2 transistors. The maximum drain current of the HfO2/Al2normalO3 MIS–HFETs has increased by ∼8.5% , while the off-state drain current has reduced by nearly 1 order of magnitude than that of the HfO2 MIS–HFETs. After the thermal stress at elevated temperatures (400 and 500°C ) for a prolonged duration up to 500 min, the irreversible device performance degradation, including drain current, peak transconductance, threshold voltage, and gate leakage current for the HfO2/Al2normalO3 MIS–HFETs, is substantially less than that for the HfO2 MIS–HFETs. A longer lifetime of ∼4×106h at 150°C has also been estimated for the former, compared to that of the latter of ∼2×105h .

Capacitance–Voltage Characteristics of Al2O3/AlGaN/GaN Structures and State Density Distribution at Al2O3/AlGaN Interface

“…Gate insulator materials, such as SiO 2 , 3,7-9) Si 3 N 4 , 4,10-13) Al 2 O 3 , 5,6,[14][15][16][17][18] HfO 2 , [19][20][21][22] ZrO 2 , 22,23) and Ga 2 O 3 , 24) have thus far been characterized [Fig. 1(b)].…”

Hafnium Aluminate–Polymer Bilayer Dielectrics for Organic Light-Emitting Transistors (OLETs)

“…40,41 Likewise, FETs fabricated with nanolaminates (i.e., dielectric bilayers composed by Al 2 O 3 and HfO 2 ) in combination with inorganic semiconductors like AlGaN/GaN or IGZO (indium gallium zinc oxide) showed lower leakage current, smaller threshold voltage, and a higher ON/OFF ratio when compared to single-oxide layers devices. 30,31,42,43 Integrating these dielectric materials in organic lightemitting transistors is currently yet not very much studied; however, literature works on (organic) field-effect transistors suggest that using higher capacitance dielectrics (and in particular high-k dielectrics) can expectedly lead to an overall improvement of the device (opto) electronic properties.…”

“…Similarly, bilayer dielectric stacks have also been investigated. For instance, a bilayer composed of ALD layers (Al 2 O 3 and HfO 2 nanolaminate) and an amorphous fluoropolymer (CYTOP) has shown improved environmental stability and better performance, including reduction of the threshold voltage (<2 V) and hysteresis, and high mobility values in different OFET configurations. , Likewise, FETs fabricated with nanolaminates (i.e., dielectric bilayers composed by Al 2 O 3 and HfO 2 ) in combination with inorganic semiconductors like AlGaN/GaN or IGZO (indium gallium zinc oxide) showed lower leakage current, smaller threshold voltage, and a higher ON/OFF ratio when compared to single-oxide layers devices. ,,, …”

Method of evaluating interface traps in Al2O3/AlGaN/GaN high electron mobility transistors*

“…When the gate is driven with a forward bias, [1][2][3] GaNbased metal-insulator-semiconductor (MIS) high electron mobility transistor (HEMT) can effectively suppress the gate leakage current and enlarge the gate voltage swing and, therefore, it is attractive to high-voltage and high-power applications. Among all the commonly used dielectric materials such as Si 3 N 4 , [4][5][6] SiO 2 , [7][8][9] Al 2 O 3 , [10][11][12][13] HfO 2 , [14][15][16] ZrO 2 , [17] and Ta 2 O 5 , [18][19][20] the Al 2 O 3 is one of the leading candidates for gate insulator in GaN-based devices due to its large bandgap (7 eV-9 eV), high dielectric constant (8)(9)(10), and high breakdown field (10 MV/cm). [21][22][23] In Table 1 the high-k dielectric material properties are summarized, such as bandgap, dielectric constant and breakdown field.…”