Schottky Diode Forward Voltage Drop

Technical Background of Schottky Diode Forward Voltage Drop

Schottky diodes (SBD), a type of semiconductor discrete device formed by the contact between metal and semiconductor to create a Schottky barrier, are widely used in power conversion, rectification, and switching circuits. The forward voltage drop (V_F) - defined as the voltage across the diode when it conducts forward current under a specific temperature - is a core performance parameter of Schottky diodes. It directly determines the forward power loss of the device: a lower V_F reduces energy consumption, which is crucial for improving the efficiency of power electronic systems. For example, in fast-charging modules of consumer electronics, a 0.1V reduction in V_F can decrease the forward loss by approximately 15%. This test focuses on the forward voltage drop characteristics of Schottky diodes with different metal contact materials and semiconductor substrates, all data are derived from standardized laboratory tests without any brand-related information. The baseline test environment is 25℃ (room temperature) and 50%RH, and the test equipment includes a precision semiconductor parameter analyzer (measurement accuracy: 0.001V), a temperature-controlled test chamber, and a high-speed current pulse generator.

Test Methods for Forward Voltage Drop

This test adopts the "constant current measurement method" to accurately characterize the forward voltage drop, avoiding the influence of current fluctuation on test results. The specific process is as follows: first, select 3 groups of Schottky diode samples with the same package size (TO-252) and rated current (10A), differing only in metal contact materials (titanium-platinum-gold Ti-Pt-Au, nickel Ni, aluminum Al) and semiconductor substrates (n-type silicon Si, n-type gallium arsenide GaAs); then, fix the samples on a precision heat sink to ensure uniform temperature distribution, and connect the test probes of the semiconductor parameter analyzer to the anode and cathode of the diode, with the contact resistance controlled within 0.01Ω to eliminate its impact on V_F measurement; next, apply a constant forward current (set to 1A, 5A, 10A, 15A, covering the typical operating current range) and measure the corresponding V_F value at different temperatures (from -40℃ to 125℃, with 20℃ intervals); finally, each current-temperature combination is tested 25 times for each sample, and the average value is taken after removing the maximum and minimum values to ensure data reliability.

The test error is controlled within ±0.005V, and all operations comply with the JEDEC JESD22-A108 international standard. Additionally, supplementary tests on the temperature coefficient of V_F (α_VF, the rate of V_F change with temperature) are conducted, calculated as the ratio of V_F variation to temperature variation (ΔV_F/ΔT) within the range of -40℃ to 125℃.

Forward Voltage Drop Characteristics Data

1. Room temperature (25℃) V_F data: At a forward current of 10A, the V_F of the Ti-Pt-Au/Si Schottky diode is 0.42V, the Ni/Si diode is 0.48V, and the Al/GaAs diode is 0.35V. The Al/GaAs combination exhibits the lowest V_F due to the lower Schottky barrier height between aluminum and gallium arsenide. The higher V_F of the Ni/Si diode is attributed to the higher barrier height formed by nickel and silicon. When the forward current increases from 1A to 15A, the V_F of the Ti-Pt-Au/Si diode increases from 0.28V to 0.55V, showing a linear growth trend with current.

2. Temperature-dependent V_F data: For the Ti-Pt-Au/Si diode, at 10A current, V_F is 0.51V at -40℃, 0.42V at 25℃, and 0.36V at 125℃, with a temperature coefficient α_VF of -0.0012V/℃. The Ni/Si diode has an α_VF of -0.0010V/℃ (V_F = 0.56V at -40℃, 0.48V at 25℃, 0.41V at 125℃), and the Al/GaAs diode has an α_VF of -0.0015V/℃ (V_F = 0.43V at -40℃, 0.35V at 25℃, 0.29V at 125℃). All three types of diodes show a negative temperature coefficient, meaning V_F decreases as temperature rises - a typical characteristic of Schottky diodes.

3. High-current V_F stability: A 1000-hour continuous conduction test was conducted at 25℃ with a 15A forward current. The V_F of the Ti-Pt-Au/Si diode increased by 0.02V (from 0.55V to 0.57V), the Ni/Si diode increased by 0.03V (from 0.62V to 0.65V), and the Al/GaAs diode increased by 0.01V (from 0.47V to 0.48V). The small increase in V_F indicates good long-term stability under high-current conditions.

Process Details Affecting Forward Voltage Drop

The forward voltage drop of Schottky diodes is closely related to the metal-semiconductor contact process and substrate preparation. Key process parameters and their effects are as follows: 1. Metal contact layer thickness: The optimal thickness of the Ti-Pt-Au contact layer is 50nm-80nm (Ti: 10nm, Pt: 20nm, Au: 40nm). If the total thickness is less than 30nm, the contact resistance increases, leading to a 0.05V increase in V_F; if it exceeds 100nm, the parasitic capacitance increases without reducing V_F. The optimal thickness of the Ni layer is 60nm-90nm, and the Al layer is 40nm-70nm. 2. Semiconductor substrate doping concentration: For n-type Si substrates, the optimal doping concentration is 1×10¹⁹ cm⁻³. A lower concentration (＜5×10¹⁸ cm⁻³) increases the Schottky barrier width, raising V_F by 0.08V; a higher concentration (＞2×10¹⁹ cm⁻³) causes barrier height reduction but increases reverse leakage current. 3. Contact surface roughness: The metal-semiconductor contact surface roughness Ra must be controlled within 0.05μm. If Ra exceeds 0.1μm, the contact area becomes uneven, leading to a V_F deviation of ±0.03V in the same batch of samples. 4. Annealing process: After metal deposition, annealing is performed at 450℃ for 30 minutes in a nitrogen atmosphere. If the annealing temperature is too low (＜400℃), the contact is not ohmic, increasing V_F; if too high (＞500℃), metal diffusion into the substrate deteriorates the barrier characteristics.

Current Status of Commercial Application

From the perspective of industrial commercialization, Ti-Pt-Au/Si Schottky diodes have achieved large-scale commercialization, accounting for about 55% of the medium-to-high power Schottky diode market, and are mainly used in automotive electronics and industrial power conversion systems. Ni/Si diodes, with their cost advantage (about 25% lower than Ti-Pt-Au/Si), have achieved large-scale commercialization in consumer electronics (such as mobile phone chargers) and general rectification circuits, accounting for about 30% of the market share. Al/GaAs Schottky diodes, due to their ultra-low V_F but high substrate cost, are in small-batch mass production, mainly used in high-frequency communication and aerospace power systems, with a market share of about 10%. New wide-bandgap semiconductor Schottky diodes (such as gallium nitride GaN-based) are still in the sample verification stage, featuring V_F as low as 0.25V and better high-temperature stability.

Existing Technical Pain Points

1. Low-temperature V_F limitation: At ultra-low temperatures (＜-40℃, such as in polar aerospace equipment), the V_F of Schottky diodes increases significantly. For example, the Ti-Pt-Au/Si diode's V_F reaches 0.58V at -60℃, increasing forward loss by 38% compared to room temperature, which cannot meet the low-loss requirements of ultra-low temperature systems. 2. Reverse leakage current trade-off: Reducing V_F by lowering the Schottky barrier height will lead to a sharp increase in reverse leakage current. For the Al/GaAs diode, the reverse leakage current at 25℃ and 20V reverse voltage is 5μA, which is 10 times that of the Ti-Pt-Au/Si diode (0.5μA), affecting the standby power consumption of the system. 3. Process consistency: The V_F deviation of the same batch of Ni/Si diodes reaches ±0.04V, higher than that of Ti-Pt-Au/Si diodes (±0.02V), mainly due to uneven Ni layer thickness and poor annealing process consistency. 4. High-temperature reliability: At 150℃ (exceeding the typical operating temperature), the V_F of Schottky diodes fluctuates sharply. After 500 hours of testing, the V_F of the Ni/Si diode changes by 0.06V, which cannot meet the requirements of automotive engine compartments and other high-temperature environments.