超低功率之高頻砷化銦通道高電子遷移率電晶體之研究

Abstract

在本論文中，高效率的砷化銦通道高電子遷移率電晶體被製造並評估其高頻、低功率消耗的應用。使用次微米線寬閘極與最佳化的磊晶結構，大幅提昇了砷化銦通道高電子遷移率電晶體元件特性。在本論文中也詳細探討元件佈局對整體特性的影響。 本論文中砷化銦鋁/砷化銦鎵功率高電子遷移率電晶體在使用70奈米的T型閘極與double δ-doping之元件也被成功的製作與研究。因具備奈米尺寸的閘極與銦含量高達60%的通道層，此電晶體具有890 mA/mm的飽和汲極-源極電流以及827mS/mm的轉導值，並展現200GHz的高截止頻率(fT)與300GHz的最高震盪頻率(fmax)。此元件在32 GHz之Ka頻段下具有良好的特性，表現出14.5 dBm (176 mW/mm) 的最大輸出功率對應11.1dBm (80 mW/mm) 的P1dB，以及9.5dB的功率增益。 為了進一步提昇元件特性，通道層的銦含量提高到百分之百成了砷化銦通道高電子遷移率電晶體，當元件操作在0.7伏特的低偏壓時，砷化銦的高速特性使得元件的截止頻率被提升到310 GHz而最高震盪頻率也提高到了330 GHz，而內部的延遲時間只有0.63兆分之一秒。另一方面在量測時過高的操作偏壓會伴隨著載通道層內的載子撞擊離子化現象，此一現象會造成元件特性劣化。因此元件操作時必須避免撞擊離子化現象以得到最好的操作特性。此元件經過評估後，展現出高速、低消耗功率邏輯應用的潛力。 為了符合超低消耗功率的需求，我們評估了砷化銦通道高電子遷移率電晶體在超低功率低雜音放大器的應用。在0.2伏特的低電壓操作下，透過小訊號S參數量測此元件展現出120 GHz的高截止頻率以及157 GHz的最高震盪頻率。在消耗功率只有1.2 mW的偏壓條件與12ＧＨz的操作頻率下，元件展現出9.7dB的高增益以及0.8dB的低雜音指數。與其他的砷化銦鎵通道層元件相比，本論文中的砷化銦元件展現出較高的增益以及較低的雜音指數。此結果指出砷化銦元件適用於超低功率的太空雷達、攜帶用釐米波通訊裝置與手持影像裝置等應用。 為了延續摩爾定律、找尋下一世代取代矽互補式金氧半導體電晶體的替代品，應用原子層沈積法所成長的氧化鋁被使用在砷化銦高電子遷移率電晶體上當作閘極介電層。比較氧化鋁極介電層使用前與使用後，可找出元件的最佳磊晶結構以符合高速、低消耗功率的需求。

High performance InAs-channel high electron mobility transistors (HEMTs) have been fabricated and characterized for high frequency and high speed logic low-power consumption applications. The performance of the InAs-channel HEMTs was improved by optimizing the device structure and using a sub-micron gate. The epi-structure, layout design and electrical measurements of the devices are discussed in details in this dissertation. In this study, a 70-nm In0.52Al0.48As/In0.6Ga0.4As power MHEMT with double δ-doping was fabricated and evaluated. The device has a high transconductance of 827 mS/mm. The saturated drain-source current of the device is 890 mA/mm. A current gain cutoff frequency (fT) of 200 GHz and a maximum oscillation frequency (fmax) of 300 GHz were achieved due to the nanometer gate length used and the high Indium content in the channel. When measured at 32 GHz, the 0.07 × 160 μm¬2 device demonstrates maximum output power of 14.5 dBm (176 mW/mm) and P1dB of 11.1 dBm (80 mW/mm) with 9.5 dB power gain. The excellent DC and RF performance of the 70-nm MHEMT shows a great potential for Ka-band power applications. In order to further enhance the performance, the indium content of the InxGa1-xAs channel was increased to 100 % to form an InAs-channel HEMT. A high current gain cutoff frequency (ft) of 310 GHz and a high maximum oscillation frequency (fmax) of 330 GHz were obtained at VDS = 0.7 V due to the high electron mobility in the InAs channel. Performance degradation was observed on the cutoff frequency (ft) and the corresponding gate delay time for logic applications caused by impact ionization due to a low energy bandgap in the InAs channel. DC and RF characterizations on the device have been performed to determine the proper bias conditions in avoidance of the performance degradations due to the impact ionization. With the design of InGaAs/InAs/InGaAs composite channel, the impact ionization was not observed until the drain bias reached 0.7 volt, and at this bias the device demonstrated very low gate delay time of 0.63 psec. The high performance of the InAs/InGaAs HEMTs demonstrated in this study shows its great potential for high speed and very low power logic applications. In the issue of power consumption, InAs-channel HEMT for ultralow-power low-noise amplifier (LNA) applications has been characterized. Small-signal S-parameter measurements performed on the InAs-channel HEMT at a low drain-source voltage of 0.2 V exhibited an excellent fT of 120 GHz and an fmax of 157 GHz. At an extremely low level of dc power consumption of 1.2 mW, the device demonstrated an associated gain of 9.7 dB with a noise figure of less than 0.8 dB at 12 GHz. Such a device also demonstrated a higher associated gain and a lower noise figure than other InGaAs-channel HEMTs at extremely low dc power consumption. These results indicate the outstanding potential of InAs-channel HEMT technology for ultralow-power space-based radar, mobile millimeter-wave communications and handheld imager applications. In search of an alternative device for beyond Si-CMOS, n-type metal-oxide-semiconductor HEMT (MOS-HEMT) devices with an InAs-channel using atomic-layer-deposited Al2O3 as gate dielectric have been fabricated and characterized. Device performance of a set of scaled transistors with and without high-k gate dielectric Al2O3 have been compared to determine the optimum device structure for low-power and high-speed applications. Measurement results revealed that the high-performance InAs-channel MOS-HEMTs with ALD Al2O3 gate dielectric can be achieved if the structure is designed properly.