Performance Enhancement of Integrated Circuits and Power Devices via Embedded Diamond Heat Management Shye Shapira Phononics, Hataasiya 51 Nesher, Israel email: shye@phononicstech.com Abstract We report the manufacturing and integration of lab grown microcrystaline diamond in the wafer and package of advanced silicon integrated circuits and compound semiconductor processes. Diamond which has a thermal conductivity of 1500-2200 W/(m*K), four times higher than copper and fifteen time higher than silicon, significantly reduces the thermal spreading resistance and the junction / core temperature. We present perfomance stress test results performed on a state of the art processor with embedded diamond heat spreader showing a marked increase in processor speed and reduced core temperature when compared to a the same processor in a standard package. A marked reduction in cores temperature spread is also displayed by the diamond embedded processor. Results for power device performance improvement are also described. Index Terms —Thermal management of electronics; Diamond; Electronic packaging thermal management; Monolithic integrated circuits; Digital integrated circuits; Microwave integrated circuits; High Power Devices. I. INTRODUCTION The continuous reduction of transistor feature sizes allowing a doubling of device density every eighteen months (“Moore’s Law”) has been progressing for decades, bringing with it added technical benefits such as an increase in transistor cutoff frequencies and increased processor clock speeds. However, since the beginning of the century, processor clock speeds have hardly increased from several GHz to this day. This is while single transistor cutoff frequencies have grown by over sixfold. The main reason for the suppression of clock frequency increase with advancing in technology nodes was thermal management. [1], [2] During the progression of Moore’s law all integrated circuit platforms have been silicon and silicon on insulator based. The thermal conductivity of silicon is around 130 W/ (m*K). However, with the increase of transistor density, the power intensity generated by circuit operation increases and nowadays can reach 1-4 W/ mm^2 for integrated circuits and well over 10 fold of that for power devices in saturation mode. Consequently, without further engineering, this would result in an ever-growing chip operating temperature. Chip architects have addressed this problem partially since the beginning of the century by switching to multicore design and limiting the processor clock frequencies to prevent chip overheating. [1] Physical solutions such as in-chip microfluidic channels have not caught on for the general industry due to operation, yield and reliability complications. Thus some chip performance boost which nowadays is achieved through new architecture, and scaling to more aggressive technology nodes may be achieved by better practical cooling solutions. II. PASSIVE COOLING BY DIAMOND INTEGRATION IN PACKAGE Diamond has a heat conductivity which is the highest in nature, ranging from 1000 W/ (m*K) to 2200 W/ (m*K). It is between 10 to twenty times higher than silicon and up to five times higher than copper. Hence it can be used effectively as a heatspreader when placed in proximity to hot spots generated in electrical circuits. Such use has been reported in GaN amplifiers where diamond layers were integrated into the substrate of a GaN wafer in close proximity to the active hot spot formed at the transistor gate edge on the drain side [3]. The reduction of the spreading resistance led to a reduction in the junction temperature and hence a higher reliability lifetime and higher output power [1]. In advanced silicon integrated circuits (ICs) thermal hotspots appear in two scales. At the transistor level, heat is generated at the drain edge due to dissipation of excess carrier energy at the drain edge. The dimensions of such hotspot patterns (size and pitch) for state of the art digital technology, are on nanometer scale. To mitigate the excess heat would require integrating heat spreaders that are in a nanometer scale proximity to the hotspots. Hotspots or “hot operation areas” generated by processor cores which are of millimeter dimensions, (Fig. 1) generate in operation, excess heat that can be addressed by diamond-based heat spreaders that are further removed from the heat source. Silicon Chip Hot Operation Areas Fig. 1. Multicore processors generate hotspots on the dimensions of millimeter scale. The figure shows two cores. These are addressed by adding an integrated diamond heatspreader. III. STATE OF THE ART PROCESSOR DEMO We used a commercially available state of the art 8 core processor, released in 2021 with a clock speed of 5 GHz. We compared the performance of lidded processors before and after the integration of diamond heatspreaders by running a AIDA64 stress test while mounting the chip on a highperformance motherboard. A powerful fan cooling system with a heat pipe link between the heatsink and the cooling fins was used. The diamond heatspreaders were processed from a multicrystaline diamond wafer (Fig. 2) which is best suited for such integration as it is less brittle than single crystal diamond. 83 degrees C to 68 degrees C. The spread of the core temperature (between the 8 cores) is also significantly reduced from a standard deviation of 4.8 degrees C to 1.2 degrees C. The change of temperature is also accompanied by a performance increase. During stress the clock frequency is slightly reduced but is higher at stress by 7 % for the processor after diamond embedding. Accordingly, the core operation power is increased by 5%. Fig. 3. Core temperatures in processor at stress. Six of the 8 cores in the processor are displayed. Upon stress diamond packaged devices exhibit an operating temperature lower by 15 degrees C and smaller temperatures differences between cores, which is an important performance enabler. IV DISCUSSION OF THE OPERATION RESULTS The improvement of chip performance by diamond integration has been clearly demonstrated above. Fig. 2. Top: 100 mm CVD grown microcrystalline diamond wafer after polishing. Heat spreaders are processed from this starting material. III. PROCESSOR TEST AND RESULTS For an accurate comparison, the results described here are measurements of the same sample before and after the diamond integration. As there are many compensation mechanisms, the BIOS and stress program were prepared so that most parameters such as the fan speed and operation voltage were fixed. The operation voltage was selected so that for the original processor it was on the verge of initiating “throttling”. Throttling or dynamic frequency scaling [4] is a name for a dynamic control on short time scales of the chip clock speed when its temperature exceeds a set upper limit, normally no more than 100 degrees centigrade ( C ). The tests were performed in an environment with ambient temperature of 24 degrees C. Fig. 3 displays the temperatures of 5 (out of 8) cores as the stress test is initiated. The data is time averaged over a window of several seconds to reduce the noise in readings. As the figure shows, the inclusion of diamond heatspreaders reduces the temperature at full stress by 15 degrees C , from While only 15% of the temperature drop from the integrates is due to the packaged chip, the inclusion of diamond may affect the overall system performance by several mechanisms: 1. Spreading resistance reduction: The placement of a diamond layer in close proximity to a small dimension heat source reduces the thermal spreading resistance and hence the temperature. 2. Reduction of power below the critical power flux the heat pipe can handle: Heatpipes are physically limited by the thermal flux density they can dissipate. Current computing cores may generate a heat flux higher than the critical limit a heatpipe can handle, and hence an efficient heatspreader is required to reduce this flux below the critical value. 3. The variation of core temperature both in time and between cores reduces the processor performance. A diamond heatsprerader reduces both these variation. Another aspect of the thermal management yet to be demonstrated is the short time response on the scale of milliseconds. The inclusion of diamond, which has the highest speed of sound in nature ( 15 to 20 Kilometers/ Second) also affects the short term thermal management of the chip. The performance of processors are all affected by these factors described above and therefore display a performance enhancement well beyond the “long time” data displayed here. V DIAMOND BASED THERMAL MANAGEMENT FOR POWER DEVICES The power generated by modern IC is on the order of 1-4 W/ mm^2 . Power devices in silicon or compound semiconductor structures can reach power intensities well over tenfold of that figure. Thus, power devices need a more aggressive approach for thermal management. In a previous presentation [5] we described a thermal management solution including in wafer diamond integration that reduces a power devices operating temperature over ambient by close to 30%. REFERENCES [1] Lasse Natvig et al in “Multi- and many-cores, architectural overview for programmers “ in Programming multi‐core and many‐core computing systems Wiley 2017. [2] S. H. Fuller and L. I. Millett. Computing performance: game over or next level? Computer, 44(1):31–38, January 2011. [3] J.D. Blevins et al, “Recent Progress in GaN-on-Diamond Device Technology” Proceeding CS MANTECH Conference, May 19th - 22nd, 2014, Denver, Colorado, USA. [4] K. Moiseev, A. Kolodny and S. Wimer (September 2008). "Timing-aware power-optimal ordering of signals". ACM Transactions on Design Automation of Electronic Systems. 13 (4): 1–17 [5] S. Shapira, “Diamond Based Cooling Technologies for Electronic Systems” Chipex 2020 https://youtu.be/o1ez4O5sD_w