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A Novel 4H-Sic MESFET with a Heavily Doped Region, a Lightly Doped Region and an Insulated Region

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A Novel 4H-Sic MESFET with a Heavily Doped Region, a Lightly Doped Region and an Insulated Region micromachines Article A Novel 4H-SiC MESFET with a Heavily Doped Region, a Lightly Doped Region and an Insulated Region Hujun Jia *, Mengyu Dong , Xiaowei Wang, Shunwei Zhu and Yintang Yang School of Microelectronics, Xidian University, Xi’an 710071, China; [email protected] (M.D.); [email protected] (X.W.); [email protected] (S.Z.); [email protected] (Y.Y.) * Correspondence: [email protected]; Tel.: +86-029-8820-2562 Abstract: A novel 4H-SiC MESFET was presented, and its direct current (DC), alternating current (AC) characteristics and power added efficiency (PAE) were studied. The novel structure improves the saturation current (Idsat) and transconductance (gm) by adding a heavily doped region, reduces the gate-source capacitance (Cgs) by adding a lightly doped region and improves the breakdown voltage (Vb) by embedding an insulated region (Si3N4). Compared to the double-recessed (DR) structure, the saturation current, the transconductance, the breakdown voltage, the maximum oscillation frequency (fmax), the maximum power added efficiency and the maximum theoretical output power density (Pmax) of the novel structure is increased by 24%, 21%, 9%, 11%, 14% and 34%, respectively. Therefore, the novel structure has excellent performance and has a broader application prospect than the double recessed structure. Keywords: SiC; Metal-Semiconductor Field Effect Transistor (MESFET); heavily doped region; power added efficiency (PAE) Citation: Jia, H.; Dong, M.; Wang, X.; Zhu, S.; Yang, Y. A Novel 4H-SiC MESFET with a Heavily Doped Region, a Lightly Doped Region and 1. Introduction an Insulated Region. Micromachines The third-generation semiconductor is the development trend of the semiconductor. 2021, 12, 488. https://doi.org/ The third-generation semiconductor material is mainly divided into silicon carbide and 10.3390/mi12050488 gallium nitride. Silicon carbide is more suitable as a substrate material. Compared to the first- and second-generation semiconductors, it has a higher breakdown voltage, wider Academic Editor: Stephen band gap, higher electrical conductivity and thermal conductivity, and will replace the Edward Saddow previous two generations of semiconductor materials in some fields, such as high temper- ature, high pressure, high power, high frequency, etc. [1–3]. Due to the lack of large-size Received: 30 March 2021 single crystals of gallium nitride, the main forms of the third-generation semiconductor Accepted: 22 April 2021 Published: 26 April 2021 materials are silicon carbide-based silicon carbide epitaxial devices, silicon carbide-based gallium nitride epitaxial devices, silicon carbide is more widely used [4]. Benefiting from Publisher’s Note: MDPI stays neutral the advantages of silicon carbide materials, silicon carbide-based MESFETs have better with regard to jurisdictional claims in performance than silicon-based and gallium arsenide-based devices [5]. published maps and institutional affil- In addition, since the depletion layer isolates the carriers from the surface of the iations. device during the operation of the MESFETs, the surface of the device has a relatively small effect on the carriers. Therefore, compared with the MOSFETs, the MESFETs have higher saturated electron mobility, higher current, greater transconductance and trans- mission frequency [6]. Therefore, the application of 4H-SiC MESFET in the fields of high temperature, high voltage, high frequency and high power has received extensive attention. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. How to improve the performance of 4H-SiC MESFET has become a challenge. Methods This article is an open access article such as adding field plates [7], improving gate structure [8–10] and improving channel distributed under the terms and structure [11–14] have been used to improve the performance of devices. With the continu- conditions of the Creative Commons ous reduction in device size, the requirements of device design for power consumption Attribution (CC BY) license (https:// and efficiency become increasingly higher. In recent years, how to improve the PAE of creativecommons.org/licenses/by/ devices without significantly sacrificing DC and AC characteristics has gradually become 4.0/). an important topic [15–17]. Micromachines 2021, 12, 488. https://doi.org/10.3390/mi12050488 https://www.mdpi.com/journal/micromachines Micromachines 2021, 12, x 2 of 9 without significantly sacrificing DC and AC characteristics has gradually become an im‐ portant topic [15–17]. In this work, we propose a novel 4H‐SiC MESFET with a heavily doped region, a Micromachines 2021, 12, 488lightly doped region and an insulated region. Due to the existence of a lightly doped2 of 9 re‐ gion, heavily doped region and insulated region, the Idsat, Vb, Pmax and fmax of the novel structure are greater than those of the DR structure [18]. We also explore the maximum PAE of the devices.In this work, we propose a novel 4H-SiC MESFET with a heavily doped region, a lightly doped region and an insulated region. Due to the existence of a lightly doped 2. Deviceregion, Structure heavily and doped Simulation region and insulatedMethods region, the Idsat,Vb,Pmax and fmax of the novel structure are greater than those of the DR structure [18]. We also explore the maximum FigurePAE 1 of shows the devices. the cross‐sectional views of the DR structure and the novel structure. Compared to traditional DR structure, in addition to the substrate, buffer and channel layer, the2. Devicenovel Structurestructure and also Simulation has an additional Methods heavily doped region, a lightly doped region and anFigure insulated1 shows region the cross-sectional in the channel. views ofTable the DR 1 shows structure the and structure the novel parameters structure. of the devices.Compared to traditional DR structure, in addition to the substrate, buffer and channel layer, the novel structure also has an additional heavily doped region, a lightly doped region and an insulated region in the channel. Table1 shows the structure parameters of the devices. Source Drain Gate + 0.2 µm + N 0.5 µm0.7 µm 1.0 µm N 0.5 µm 0.05 µm 0.5 µm 0.3 µm 0.25 µm 0.35 µm N-Channel P - B u ffe r Sem i-insulating substrate (a) Source Drain Gate + 0.2 µm + N 0.5 µm0.7 µm 1.0 µm N 0.5 µm N - Si N d 0.5 µm 0.3 µm 3 4 1 0.25 µm L1 L2 L3 + N d2 N -C hannel L4 P-Buffer S em i-insu lating substrate (b) Figure 1.Figure Cross 1.‐sectionalCross-sectional diagrams diagrams of (a of) the (a) the DR DR structure structure and and ((bb)) the the proposed proposed structure. structure. The novel structure can be made using similar processes to those reported in [19]. The heavily doped region and lightly doped region can be formed by ion implantation and activation processes. The fabrication of the insulated region can refer to the process steps described in [10]. First, the location of the metal gate and insulating area is created by etching; then, the oxide layer is grown on the surface and the silicon nitride is etched Micromachines 2021, 12, 488 3 of 9 Table 1. Structure parameters of the devices. Parameter Value Thickness of source/drain 0.2 µm Length of source/drain 0.5 µm Doping of source/drain 1 × 1020 cm−3 Doping of channel 3 × 1017 cm−3 Thickness of buffer 0.5 µm Doping of buffer 1.4 × 1015 cm−3 Doping of lightly doped region 1 × 1015 cm−3 Doping of heavily doped region 5 × 1019 cm−3 L1 0.2 µm L2 0.2 µm L3 0.8 µm L4 0.5 µm d1 0.06 µm d 0.1 µm Micromachines 2021, 12, x 2 3 of 9 The novel structure can be made using similar processes to those reported in [19]. The heavily doped region and lightly doped region can be formed by ion implantation and andactivation deposited processes. by using The a fabricationmask, and of finally, the insulated the metal region gate can is refer manufactured to the process by steps a similar method.described in [10]. First, the location of the metal gate and insulating area is created by etching;Two‐dimensional then, the oxide numerical layer is grown simulation on the surface of these and structures the silicon nitridewas carried is etched out and by ISE‐ TCADdeposited software. by using As athe mask, process and finally, of SiC the material metal gate in ADS is manufactured software is by not a similar perfect method. at present, while theTwo-dimensional process of GaAs numerical material simulation is mature, of we these fit structures the model was of carriedSiC MESFET out by by ISE- modi‐ fyingTCAD the software.model parameters As the process of GaAs of SiC MESFET, material in so ADS that software it could is better not perfect reflect at present,the trend of while the process of GaAs material is mature, we fit the model of SiC MESFET by modifying power added efficiency of devices. After the device model is established, it needs to be the model parameters of GaAs MESFET, so that it could better reflect the trend of power verified,added and efficiency the “ads_templates: of devices. After FET_curve_tracer” the device model is established,module in ADS it needs was to used be verified, to measure its andIV characteristics; the “ads_templates: the measurement FET_curve_tracer” results module were in compared ADS was used with to those measure in ISE its‐ IVTCAD. Thecharacteristics; results are shown the measurement in Figure 2. resultsIt can be were seen compared that the withIV characteristic those in ISE-TCAD. curve of The devices in resultsADS is are in showngood agreement in Figure2. It with can bethat seen in that ISE the‐TCAD. IV characteristic Therefore, curve we used of devices the EE_FET3 in modelADS of is nonlinear in good agreement GaAsFET with model that in in ISE-TCAD.
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