Comparison of Double-gate Junctionless and Traditional MOSFETs by Means of TCAD

 
Chaplygin Yu.A., Krupkina T.Yu., Korolev M.A., Krasukov A.Yu., Artamonova Ye.A. (MIET)
 
Abstract - Paper represents the results of TCAD [1-2] comparison of the electrical characteristics of 90 nm double-gate JAM and IM MOSFETs, in particular saturation currents, subthreshold currents, subthreshold slopes, threshold voltages. The junctionless accumulation-mode (JAM) transistor has been recently proposed as an alternative to conventional inversion-mode (IM) MOSFET due to the simplified processing and higher mobility. JAM construction includes highly doped channel region which is the same type as the source/drain (S/D) regions. Due to the absence of p-n-junctions, it is not subject to short-channel effects [3-8]. 2D models of 90 nm double-gate JAM and IM MOSFETs have been created and studied by means of Sentaurus TCAD. Devices have the following parameters: substrate thickness 70 nm, gate oxide thickness 2.1-5 nm, channel length 90 nm, n+ gate for IM MOSFET and p+ gate for JAM MOSFET, spacers length 25 nm, source-drain concentration 1020 cm-3, n-LDD concentration 5•1018 cm-3. Study of electron concentration distribution in the transistor’s channel obtained by TCAD shows that in off-state (at Vgs = 0.2 V and Vds = 1.2 V) the channel of JAM MOSFET is completely depleted by electrons throughout its thickness due to the influence of the contact potential difference of the MOS gate structures forming the interlocking space-charge regions. In on-state (at Vgs = Vds = 1.2 V) the channel of JAM MOSFET is conductive over its entire thickness (there are no space-charge region) while IM MOSFET has electron concentration maximus only near the Si-SiO2 interface (inversion channels). At the same time, estimates shows that the transistors have comparable values of electron charge density in the channel. The dependences of threshold voltages, saturation currents, leakage currents and subthreshold slopes from the channel doping have been calculated. Additionally, the comparison of channel doping concentrations, threshold voltage variations (DIBL-effect parameters), leakage currents, saturation currents and subthreshold slopes of IM and JAM MOSFETs at gate oxide thicknesses 2.1 nm and 5 nm is given. Comparison of the electrical characteristics of 90 nm IM MOSFET and 90 nm JAM MOSFET with reduced channel doping 1017 cm-3 shows: - channel doping concentration of JAM MOSFET at threshold voltage 0.45 V and drain-source 1.2 V is much less than for IM MOSFET; - at gate oxide thickness 2.1 nm the studied transistors have comparable values of the threshold voltage variations; - JAM MOSFET saturation current 310 µA/µm is smaller than thus for IM MOSFET, however it is enough for standard 90 nm technology; - subthreshold current of JAM MOSFET is 5•10-13 A/µm what is five orders lower than IM MOSFET shows; - subthreshold slope of JAM MOSFET is 75 mV/dec what is three orders lower than in IM MOSFET and it weakly depends on the channel doping and gate oxide thickness in the required range 2.1-5 nm.

Keywords - double-gate junctionless MOSFET, simulation, TCAD, electrical characteristics.

Сравнительный анализ двухзатворных беспереходного и традиционного МОП-транзисторов средствами TCAD

 
Чаплыгин Ю.А., Крупкина Т.Ю., Королев М.А., Красюков А.Ю., Артамонова Е.А. (Национальный исследовательский университет «МИЭТ», г. Москва)
 
Аннотация - Проведен сравнительный анализ электрических характеристик двухзатворных беспереходного и традиционного МОП-транзистора с проектными нормами 90 нм. Отмечены недостатки беспереходного транзистора, обусловленные высоким уровнем легирования его канала. С использованием средств TCAD показано, что при умеренном уровне легирования канала беспереходного транзистора, прибор имеет существенно меньшие токи утечки и подпороговый наклон по сравнению с обычным двухзатворным инверсионным МОП-транзистором при сопоставимых значениях порогового напряжения и тока насыщения.

Ключевые слова - двухзатворный беспереходной МОП-транзистор, моделирование, TCAD, электрические характеристики.