This paper names some alternatives available:
- a linear trend (something like assuming constant exogenous growth)
- ICT capital
- stock of patents
- stock of knowledge (proxied by education levels or human capital)
- energy prices (e.g. see here)
This article mentions the following proxies for technological change:
the NBER productivity series, the Census of Manufacturers series on investment in computers, the industry's research and design to sales ratio, the industry's use of patents, and the number of scientists and engineers employed within the industry.
If you want homogeneous, long and wide coverage, the best option might be the World Bank Development Indicators for science and technology. Some of them have been mentioned above. See the database here, and here is a paper using them to study their importance on technical change.
A dataset which is also quite popular at the moment is that of robots, compiled by the International Federation of Robotics. The logic is the same than that of using ICT (notice both of these could be considered as capital too). For example, see here. The authors state:
The IFR provides data on the number of robots delivered to each industry, in each country and year. We construct the stock of robots based on the deliveries using the perpetual inventory method, assuming a depreciation rate of ten percent. This approach is similar to the EUKLEMS procedure for computing the stock of ICT capital.