Namcheol Jeon

Improvement of

In this letter, reduction of threshold voltage instability in gate recessed normally-off GaN metal insulator semiconductor high electron mobility transistors with SiNx gate insulator was investigated. A plasma enhanced atomic layer deposition technique was successfully employed for very thin SiNx (5 nm) as an interfacial layer. The hysteresis and drift of threshold voltage in transfer curve and the forward biased gate leakage current were effectively reduced.

V_{\rm th}

The reduction in the gate leakage current and the improvement in subthreshold characteristics and current collapse in AlGaN/GaN high-electron-mobility transistors (HEMTs) with various surface treatments were investigated. We applied wet treatment, digital etching (O2 or N2O), or plasma treatment (CF4 or SF6) before SiNx passivation. Among these treatments, SF6 plasma treatment suppressed gate leakage current, reduced subthreshold slope, and improved pulsed current–voltage (I–V) characteristics most effectively.

Instability in Normally-Off GaN MIS-HEMTs Employing

Embedded capacitors with available capacitances up to � 80 nF have been implemented on a thin-film multichip moduledeposited (MCM-D) substrate. By cost-effective silicon wet etching, a new metal–insulator–metal (MIM) structure named quasi-three-dimensional MIM capacitor has been realized. The groove structure formed by silicon wet etching increases effective capacitance area, thus enhancing capacitance density by 1.5 times. No additional mask or process step is required to form the groove structure since it is simultaneously patterned and etched with ground bumps that are for effective interconnection. The implemented capacitors have capacitances from 2 to 78 nF with a scalable density of 3.6 nF/mm 2 , indicating that they are excellent candidates for high-power decoupling application. [DOI: 10.1143/JJAP.47.2535]

{\rm PEALD}\hbox{-}{\rm SiN}_{\rm x}

An investigation of threshold voltage instability in gate recessed normally-off GaN metal insulator semiconductor high electron mobility transistors (MIS-HEMTs) was performed by analyzing the interface states, border traps, and conduction band offset. To reduce the threshold voltage instability with improved dielectric-GaN interface, plasma enhanced atomic layer deposition (PEALD) technique was successfully employed for very thin SiNx (5nm) as an interfacial layer. Forward biased gate leakage current, capacitance-voltage measurements, and current-transient analysis were performed to find the reason for this improvement. Finally, we proposed an importance of border traps and the conduction band offset which is related to trapping mechanism in transfer characteristics.

as an Interfacial Layer

This paper presents a gallium nitride (GaN)-based hybrid current-mode class-S (CMCS) power amplifier (PA) using a bandpass delta-sigma modulator (BPDSM) for a 955-MHz LTE signal. To enhance the drain efficiency of the CMCS PA, the chip-on-board (COB) technique, which can reduce the external parasitic components of the packaged transistor and allow fast switching operation at high frequencies by minimizing distortion of the pulse waveform, is adopted. Also, GaN Schottky barrier diodes are fabricated in-house to protect the switching transistor against the high negative voltage swing. The differential output filter and balun composed of lumped LC resonators are integrated at the back of the switching transistor to extract amplified LTE signal from the output rectangular waveform, and the fabricated CMCS PA is measured and analyzed at four different states of BPDSM according to the coding efficiency from different input power level to obtain higher power and efficiency. Finally, a cavity bandpass filter (BPF) is added to the output circuit for a more accurate reduction of the harmonics and out-of-band noise signals to enhance system efficiency. From the measured results for an 8.5-dB PAPR 3 G LTE 10-MHz input signal, the proposed CMCS PA has a maximum average output power of 37.61 and 30.78 dBm, and the resulting drain efficiencies of 33.3% and 38.6% with the drain voltage of 19 and 7 V, respectively.

Effects of various surface treatments on gate leakage, subthreshold slope, and current collapse in AlGaN/GaN high-electron-mobility transistors

Integrated antennas operating at millimeter-wave (mm-wave) frequency have been implemented on a benzocyclobutene (BCB)-based system-on-package (SOP) substrate. A novel BCB-based SOP substrate with a Si bump and a Si cavity was proposed to increase the BCB thickness, thus enhancing the gain of the microstrip patch array antenna and reducing the transfer loss of the transmission line. The mechanical issues of adhesion and stress of BCB are studied. The adhesion between gold and BCB was improved significantly by the insertion of a layer of Si oxide (SiO2) by plasma-enhanced chemical vapor deposition (PECVD). SiO2 can also reduce the wafer bow by stress compensation. Wafer bow of whole structure was decreased from 79.3 to 55.2 µm by the insertion of a 1-µm-thick SiO2 layer. A series-fed 1 ×8 linear array antenna is impedance matched well at 77 GHz. The process flow including BCB chemical mechanical polishing (CMP) was described. The proposed SOP substrate can be a candidate for overcoming the constraint of BCB thickness.

Embedded Decoupling Capacitors up to 80 nF on Multichip Module-Deposited with Quasi-Three-Dimensional Metal?Insulator?Metal Structure

Abstract An effective digital etching technique and its application on fully recessed Schottky barrier diode (SBD) are described in this paper. Etch rate and roughness of the digitally etched Al0.25GaN surface were 0.6 nm/cycle and 0.58-nm which is almost identical with a non-recessed surface. Hall-effect measurement revealed a negligible damage on GaN surface was generated after digital etching. Fabricated SBD with a digital etching showed an improved Schottky contact which has ideality factor of 1.19 and Schottky barrier height of 0.73 eV, respectively. The on-resistance and reverse breakdown voltage were 1.13 mΩ-cm and 566 V, respectively.

Impacts of conduction band offset and border traps on V th instability of gate recessed normally-off GaN MIS-HEMTs

The development of cross-coupled bandpass filters and a duplexer for W-band transceiver applications on a thin-film substrate is presented. The filter is designed at 94 GHz using the cross-coupling method on a planar thin-film microstrip (TFMS) line platform and fabricated with a thin-film multichip module technology. The developed filter has an insertion loss of 2.5 dB with a 3-dB fractional bandwidth of 12.8%. Combining two cross-coupled filters with T-junction matching, a simple W-band duplexer is developed. The two channels of the duplexer are centered at 80 GHz and 94 GHz having channel bandwidth of 6.5 GHz and 6.7 GHz, respectively, with insertion loss less than 4.3 dB in both channel. The developed passives are compact and show good matching, selectivity, and isolation characteristics, and are suitable for low-cost W-band front-end integration.

Hybrid Current-Mode Class-S Power Amplifier With GaN Schottky Diode Using Chip-On-Board Technique for 955 MHz LTE Signal

In this paper, we evaluated the electrical characteristics of AlGaN/GaN Metal Insulator Semiconductor high electron mobility transistors (MIS-HEMTs) with SiNx using the two different precursors (ammonia and nitrogen) in Inductively-Coupled Plasma Chemical Vapor Deposition (ICP-CVD) as gate insulator. Much less hysteresis was successfully obtained in NH3-SiNx MIS-HEMTs, which is closely interlinked with the reliability issues. Compared to N2-SiNx MIS-HEMTs, the improved characteristics of NH3-SINx MIS-HEMTs are discussed through capacitance-voltage (C-V) and current-voltage (I-V) hysteresis, I-V characteristics and the extraction of interface state density (Dit).

System-on-Package Platform with Thick Benzocyclobutene Layer for Millimeter-Wave Antenna Application

A reduction of the gate leakage current, improvement of subthreshold characteristics, and good current collapse for AlGaN/GaN high electron mobility transistors (HEMT) with SF6 plasma treatment are reported. CF4 plasma treatment is frequently applied to reduce gate leakage current, but it results in positive shift of the threshold voltage and degradation of pulsed I-V characteristics. Therefore, we applied SF6 plasma treatment, O2 and N2O digital etching prior to SiNx passivation to reduce the gate leakage current without degradation of the current-voltage (I-V) characteristics of the HEMTs.