How do monolithically integrated GaN power ICs increase power density and reduce component count?

Monolithically integrated GaN power ICs offer significant advantages over traditional silicon chips, including superior efficiency, smaller size, higher speed, and reduced cost. What makes GaN so special are its natural properties, like a higher critical electric field, lower on-resistance, and smaller parasitic capacitance.

Semiconductor engineers are now employing a smart approach called monolithic integration, which involves building all the circuit components together on a single chip, rather than connecting separate pieces. Engineers typically build these systems on specialized platforms called GaN-on-Si or GaN-on-SOI wafers, which serve as the foundation for everything else built on top of it.

Figure 1. Monolithic integration approach for GaN power ICs: (a) complete fabrication process flow from donor wafer through final metal gate formation, (b) structural implementation of 3D GaN-Si CMOS integration, (c) physical layout and electrical schematic of GaN unit cell. (Image: KnowMade)

The foundation of this technology, as shown in Figures 1(a) and 1 (b), is a new gate-last process flow for 3D monolithic integration of GaN and Si CMOS that utilizes layer transfer technology. This advanced manufacturing process allows engineers to combine Si PMOS transistors with GaN transistors on the same chip while keeping a high figure of merit.

A major benefit of this approach is that it circumvents the complex fabrication of p-channel GaN devices, which means engineers don’t have to create the difficult p-type GaN components that would normally be needed in a fully GaN-based device.

Let’s look at how such an approach leads to two benefits that have been fundamental to power electronics.

How does power density increase with monolithic integration?

Increased power density is achieved by making the power converters physically smaller and enabling them to handle more power within that reduced volume. This is largely achieved due to efficiency gains and higher operating frequencies.

Physical size reduction: monolithic integration trims the size of the chip and leads to reduced volume by consolidating multiple functions into a single IC. This enables compact designs, such as nano-sized control units and smaller pixel sizes in display applications.
Suppression of parasitic inductance: in discrete power blocks, external inductances from wire bonds, solder bumps, and PCB traces impede the charging and discharging of the power transistor gate capacitance, slowing switching and increasing commutation losses.
1. Common source inductance is particularly problematic, as it induces a voltage that directly opposes the gate-source voltage during turn-on, thereby slowing current commutation and increasing switching losses.
2. By integrating the gate driver with the power transistor, these external parasitic inductances are removed from the gate drive. This allows the IC designer to minimize the internal common source inductance to an absolute minimum.
3. An important advantage of monolithic integration is the reduction or elimination of external common-source inductance and other gate-drive loop inductances. This phenomenon is illustrated in Figure 2:

Figure 2. Gate drive loop configurations showing inductance reduction benefits of GaN integration: (a,b) discrete implementations with significant stray inductances vs. (c,d) integrated GaN solutions with minimized parasitic inductances. (Image: EPC Corp. Inc.)

Faster switching speeds and higher operating frequencies: the reduction in parasitic inductances enables faster current commutation speeds. Figure 3 shows that GaN devices inherently switch faster. GaN also exhibits lower on-resistance and smaller parasitic capacitance compared to its silicon counterparts. This capability is further enhanced by monolithic integration, allowing operation at higher frequencies (e.g., from 100 kHz up to 3 MHz for various applications). Higher switching frequencies enable the use of smaller passive components, resulting in a more compact system and, consequently, higher power density.

Figure 3. GaN IC double pulse test: (a) circuit schematic, (b) packaged device, (c) test PCB, (d) 10 ns switching transitions enabling high-frequency, high-power-density operation. (Image: Compound Semiconductor)

Improved efficiency: monolithically integrated GaN converters can achieve high efficiencies, with reported maximums of 80% even at high temperatures up to 250°C. Improved efficiency means less power is wasted as heat, reducing thermal management requirements and allowing for a smaller, lighter system that does not require external cooling systems.

How does the component count reduce with a monolithic approach?

Monolithic integration involves fabricating multiple components onto a single semiconductor substrate, rather than using discrete components connected by external wiring. This approach reduces the number of individual parts required in a power converter system:

On-Chip integration of building blocks: instead of requiring separate half-bridges, diodes, capacitors, gate drivers, dead-time controllers, level shifters, PWM circuits, diagnostic and protection circuits, regulators, and bootstrap circuits, many or all of these can be integrated onto a single GaN power IC.
Simplified control signals: for instance, a monolithic GaN driver with a deadtime generator can operate using only one control signal, which then automatically generates the necessary complementary signals for the high-side and low-side drivers. This eliminates the need for external circuitry that would otherwise manage and preset dead times. This phenomenon is shown in Figure 4.

Figure 4. Monolithic GaN power IC schematic featuring an integrated deadtime generator and drivers, resulting in reduced component count and simplified system design. (Image: IET Wiley)

Reduced external drive circuits: integrating the gate driver directly with the power transistor simplifies the overall circuit layout and reduces the number and size of external drive circuits. This can include functions like level shifters, power-on reset, crossover protection, and delay matching, all integrated within the IC.
Self-contained functionality: this integration leads to self-contained functionality and can even lessen the requirement for external heatsinks or cooling systems in high-temperature applications.

Summary

Monolithic GaN power ICs, instead of using multiple separate parts, integrate all circuit components onto a single chip. This approach works because GaN has better natural properties than silicon. The main benefits are much higher power density and fewer components needed. Power density gets better in several ways.

First, the physical size becomes smaller. Second, parasitic inductances get reduced. Third, switching speeds increase, allowing for operating frequencies of up to 3 MHz. Fourth, efficiency reaches 80% even at very high temperatures like 250°C. The component count decreases because many separate parts are integrated into a single chip. These parts include gate drivers, dead-time controllers, level shifters, and protection circuits. When everything works together on a single chip, system design becomes significantly simpler.