| With the development of electronics industry and worldwide focus on environmental issues, electronic information systems require devices run at lower power consumption, smaller size, faster speeds, resulting in the developing trend of electronic components is integration and miniaturization. In the electronic components, Al Ga N/Ga N high electron mobility transistor(HEMT) is a hotpot of research recently, in the field of digital circuits, enhancement-mode Al Ga N/Ga N HEMT needs to be designed, this paper uses Li Nb O3(LN) ferroelectric films as gate dielectric layer to realize LN/Al Ga N/Ga N enhancement-mode HEMT. HEMT is very competitive in the field of monolithic integrated circuits and high-speed digital integrated circuits, it has excellent power performance and low noise performance, and Al Ga N/Ga N heterostructure device is by far the most important material system in HEMTs. Compared with Si and Ga As-based devices, Al Ga N/Ga N HEMT can increase the output power in a magnitude. In the high-frequency switch and digital circuits field, enhancement-mode HEMT can reduce the cost and complexity of the circuits, improve the safety of the circuits, simplify the circuit configuration. LN is a ferroelectric material which has excellent surface acoustic properties, the spontaneous polarization of LN can comsume the 2DEG in Al Ga N/Ga N semiconductor heterojunction, in order to achieve enhancement-mode HEMT. LN is ideal for integration with Ga N-based semiconductor, first LN has similar lattice structure with Ga N semiconductor; Second LN crystal has a large spontaneous polarization, as 70-80 μC/cm2; Third LN crystal has only 180 ° ferroelectric domain structure, it is one-dimensional ferroelectric materials with ferroelectric polarization only in the c-axis direction, which can boost the carrier consumption LN to Al Ga N/Ga N heterostructure semiconductor. In this paper, we explore the growth process that LN films on Ga N substrate, design HEMT device structures, use mask layer to etch gate graphics, successfully implement enhancement LN/Al Ga N/Ga N HEMT.1. Find the optimized growth process parameters using pulsed laser deposition(PLD) to grow LN films, adjusting the laser pulse energy, the pulsed laser frequency, the growth temperature, oxygen gas pressure and the film thickness and other process parameters to obtain LN film that has good crystal quality and can epitaxially grown on the Ga N substrate, the epitaxy relationship between LN film and Ga N is [10-10]LN//[1-2-10]Ga N, [1-100]LN//[11-20]Ga N. P-E testing shows LN/Ga N integrated thin film has excellent ferroelectric properties.2. Design the HEMT device structure, use annular gate which has godd isolation effect and moderate process complexity as the gate structure.3. Use electron beam evaporation to grow source and drain ohmic electrode, the electrode uses four layers structure: Ti(20nm)/Al(50nm)/Ti(40nm)/Au(100nm).4. In order to solve the problem that photoresist can not etch LN film, we design mask layer to etch LN film in the gate region, we use Mg O as etching mask layer. Using double photoresist process to produce 1.2μm thick positive photoresist that has a uniform flat, and explore optimized growth parameters PLD to grow Mg O film: pressure 2Pa, pulsed laser energy 100 m J, pulse laser frequency 2Hz, growth time 3h, film thickness 400 nm.5. Successfully produce LN/Al Ga N/Ga N HEMT which has good device structure and completely graphics, the threshold voltage(Vth) of the device is +1.3 V, proving that we realize the enhancement-mode device, the source-drain current(Id) is 30 m A/mm, transconductance(Gm) is 80 m S/mm. |
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